Congenital Cardiac Anesthesia Society
A Section of the the Society for Pediatric Anesthesia

{“questions”:{“69u77”:{“id”:”69u77″,”mediaType”:”image”,”answerType”:”text”,”imageCredit”:””,”image”:””,”imageId”:””,”video”:””,”imagePlaceholder”:””,”imagePlaceholderId”:””,”title”:”Author: Melissa Colizza, MD – Stollery Children\u2019s Hospital – Edmonton, Canada\r\n\r\nA 3-month-old infant has just undergone ventricular septal defect closure on cardiopulmonary bypass. After weaning from bypass, the rhythm strip demonstrates a narrow-complex tachycardia at a rate of 190 bpm. The CVP tracing demonstrates a large V wave and absent A wave, and transesophageal echocardiography reveals depressed left ventricular function. Which of the following treatments is MOST appropriate for management of this rhythm?”,”desc”:”EXPLANATION \r\nJunctional ectopic tachycardia (JET) is a relatively common tachyarrhythmia occurring after congenital cardiac surgery with a reported incidence of 1 to 10%. It is caused by enhanced automaticity of the atrio-ventricular (AV) node at ventricular rates greater than or equal to 160 to 170 bpm. It is characterized by a narrow QRS complex with either ventriculo-atrial (VA) dissociation or 1:1 retrograde conduction (retrograde P-waves). The etiology remains unclear but is hypothesized to result from direct mechanical trauma or indirect stretch injury to the conduction system. Risk factors include specific surgical procedures (Tetralogy of Fallot repair, ventricular septal defect closure, and atrio-ventricular septal defect repair), young age, heterotaxy syndrome and prolonged cross-clamp time. The clinical impact of JET is significant as the loss of AV synchrony often results in a decrease in cardiac output, potentially leading to prolonged intubation and hospitalization. \r\n\r\nManagement principles of JET in the post-bypass period are based on decreasing the adrenergic drive that sustains tachycardia, controlling heart rate and re-establishing AV synchrony. General measures include the following: 1) cooling to 33-35^{o<\/sup>C; 2) decreasing the dosage of or eliminating sympathomimetic drugs; and 3) correcting electrolyte abnormalities, in particular calcium, magnesium, and potassium. Overdrive pacing involves temporarily pacing the heart at a rate that is 10-20 bpm over the underlying rate in order change the refractory period and terminate the tachyarrhythmia. It is less effective for termination of automatic tachyarrhythmias versus re-entrant tachyarrhythmias. Additionally, when the native rate is greater than 180-190 bpm, overdrive pacing may be detrimental, as the even faster heart rate would limit cardiac filling, decrease cardiac output, and cause significant hypotension.\r\n\r\nAmiodarone is a class III anti-arrhythmic agent with multiple mechanisms of action including the following, 1) inhibition of fast sodium channels; 2) depression of sinus node automaticity and AV nodal conduction; and 3) prolongation of the refractory period secondary potassium channels. Its use has been described in both the prevention and treatment of JET. Treatment proceeds with a loading dose of 5-10 mg\/kg over 30-60 minutes and an infusion of 5-15 mg\/kg\/day. Adverse events may include hypotension, bradycardia, AV block and rarely, cardiovascular collapse due to calcium chelation. \r\n\r\nProcainamide is a class I anti-arrhythmic drug, which acts predominantly on sodium channels. It has a shorter onset of action and half-life than amiodarone. Clinical efficacy is increased when used in conjunction with core temperature cooling. However, decreased systemic vascular resistance and inotropy occur more frequently with procainamide than amiodarone, making use of this drug less appropriate in patients with concurrently depressed ventricular function. Usual dosing includes a loading dose of 10-15 mg\/kg over 30-45 minutes and an infusion rate of 40-50 mcg\/kg\/min. \r\n\r\nOther agents are used for both prophylaxis and treatment of JET. Multiple studies have demonstrated that prophylactic dexmedetomidine, a selective a<\/em>2-agonist used for sedation, is effective at preventing JET when an infusion is started pre-incision and continued postoperatively. A prospective, randomized placebo-controlled study by El Amrousy et al demonstrated that a loading dose of dexmedetomidine of 0.5 mcg\/kg followed by a continuous infusion at 0.5 mcg\/kg\/h for 48 hours postoperatively significantly reduced the incidence of JET to 3.3% versus 16.7% in the placebo group. The study group also had a reduction in mechanical ventilation time, duration of ICU stay, and hospital length of stay. However, there was no difference in mortality rate, nor the incidence of bradycardia and\/or hypotension between the two groups. Magnesium sulfate has also shown promising utility for prophylaxis of JET in the pediatric population. A 2022 meta-analysis by Mendel et al compared the efficacy of dexmedetomidine, magnesium and amiodarone for JET prophylaxis. Although all three drugs were effective at preventing JET,only amiodarone and dexmedetomidine decreased ICU length of stay. Further, only dexmedetomidine was associated with decreased mortality. The authors concluded that dexmedetomidine may be the drug of choice for preventing JET. Other drugs used to treat JET include digoxin and sotalol, albeit with little supportive data. Ivabradine, an oral medication, is being utilized with increasing frequency as a novel treatment of postoperative JET. In a small study by Kumar et al, it was demonstrated to be effective at reducing heart rate and converting JET to sinus rhythm in five patients who were refractory to amiodarone treatment. Ivabradine is orally administered and reaches peak plasma concentration in one hour, limiting its use for terminating JET in the immediate post-bypass period.\r\n\r\nThe correct answer in this clinical scenario is amiodarone for the treatment of JET, which is demonstrated with findings on the rhythm strip and CVP tracing described in the stem. Procainamide would not be appropriate to treat JET in a patient with depressed ventricular function. No treatment is not the correct answer as JET can lead to hemodynamic instability and cardiac arrest. Overdrive pacing would have limited utility as this patient\u2019s heart rate is already quite high at 190 bpm and has a high likelihood of causing hypotension. \r\n \r\nREFERENCES \r\nValdes SO, Kim JJ, Miller-Hance WM. Arrhythmias: Diagnosis and Management. In Andropoulos DB. Anesthesia for Congenital Heart Disease<\/em>. 4th ed. USA: Wiley-Blackwell; 2023: 527-557.\r\n\r\nKylat RI, Samson RA. Junctional ectopic tachycardia in infants and children. J Arrhythm<\/em>. 2019;36(1):59-66. doi: 10.1002\/joa3.12282\r\n\r\nEl Amrousy DM, Elshmaa NS, El-Kashlan M, et al. Efficacy of Prophylactic Dexmedetomidine in Preventing Postoperative Junctional Ectopic Tachycardia After Pediatric Cardiac Surgery. J Am Heart Assoc<\/em>. 2017;6(3):e004780. doi: 10.1161\/JAHA.116.004780\r\n\r\nMendel B, Christianto C, Setiawan M, Prakoso R, Siagian SN. A Comparative Effectiveness Systematic Review and Meta-analysis of Drugs for the Prophylaxis of Junctional Ectopic Tachycardia. Curr Cardiol Rev<\/em>. 2022;18(1):e030621193817\r\n\r\nHe D, Sznycer-Taub N, Cheng Y, et al. Magnesium Lowers the Incidence of Postoperative Junctional Ectopic Tachycardia in Congenital Heart Surgical Patients: Is There a Relationship to Surgical Procedure Complexity? Pediatr Cardiol<\/em>. 2015;36(6):1179-1185. doi: 10.1007\/s00246-015-1141-5\r\n\r\nKumar V, Kumar G, Tiwari N, Joshi S, Sharma V, Ramamurthy R. Ivabradine as an Adjunct for Refractory Junctional Ectopic Tachycardia Following Pediatric Cardiac Surgery: A Preliminary Study. World J Pediatr Congenit Heart Surg<\/em>. 2019;10(6):709-714.\r\n”,”hint”:””,”answers”:{“tjr4r”:{“id”:”tjr4r”,”image”:””,”imageId”:””,”title”:”A.\tOverdrive pacing”},”6p3pj”:{“id”:”6p3pj”,”image”:””,”imageId”:””,”title”:”B.\tProcainamide”},”ijwni”:{“id”:”ijwni”,”image”:””,”imageId”:””,”title”:”C.\tAmiodarone”,”isCorrect”:”1″},”l18nr”:{“id”:”l18nr”,”image”:””,”imageId”:””,”title”:”D.\tNo treatment “}}}}}}

{“questions”:{“vebkr”:{“id”:”vebkr”,”mediaType”:”image”,”answerType”:”text”,”imageCredit”:””,”image”:”https:\/\/ccasociety.org\/wp-content\/uploads\/2024\/02\/CCAS-Image-2-15-2024.png”,”imageId”:”7135″,”video”:””,”imagePlaceholder”:””,”imagePlaceholderId”:””,”title”:”Author: Melissa Colizza – Stollery Children\u2019s Hospital – Edmonton, Canada \r\n\r\nA 9-month-old male is undergoing an intracardiac repair of a complex congenital heart defect with cardiopulmonary bypass. Following release of the aortic cross clamp and rewarming, the rhythm demonstrated below is noted on the monitor. Temporary epicardial pacing wires are placed to facilitate weaning from bypass. Which of the following pacemaker modes is MOST appropriate for the rhythm demonstrated below? \r\n”,”desc”:”EXPLANATION \r\nPersistent post-operative atrio-ventricular (AV) block is not an uncommon complication after congenital cardiac surgery, with an incidence of 0.3-3%. Several types of congenital heart defects, such as left ventricular outflow tract (LVOT) obstruction, L-transposition of the great arteries, and ventricular septal defect (VSD), increase the risk of post-operative AV block. Most of the time, post-operative AV block is transient with a recovery rate of 81% at seven days but may require temporary epicardial pacing for optimal hemodynamics. Temporary pacing may be accomplished via transvenous, transesophageal, transcutaneous or epicardial routes. Temporary epicardial pacing is used frequently after cardiac surgery, as temporary transvenous wires are more likely to get dislodged. Furthermore, transesophageal and transcutaneous pacing requires high voltages and stimulates large portions of the myocardium simultaneously. Anesthesiologists are commonly required to set and troubleshoot temporary epicardial pacemakers in the operating room. \r\n\r\nIn the context of high-grade or complete AV block, as demonstrated in the stem, there is a lack of reliable AV conduction. At a minimum, pediatric patients require an appropriate ventricular rate for their age. AAI is a mode in which an electrical current will be delivered to the atrium at a set rate if no intrinsic atrial depolarization\/voltage is sensed. However, there is no ventricular sensing or pacing involved, and ventricular contraction is dependent on intact AV conduction. Therefore, AAI is not an appropriate mode for complete heart block. VVI mode is an acceptable choice in the presence of a single ventricular lead or dysfunctional atrial wire if both ventricular and atrial wires are present. In VVI mode, an electrical current will be delivered to the ventricle at a set rate when no ventricular depolarization is sensed. In VVI mode, the absence of coordinated atrial and ventricular contraction can significantly reduce cardiac output (CO). VVI mode does not maximize cardiac output, particularly in the subset of patients who are reliant upon an \u201catrial kick\u201d. DDD mode can be used in patients with both atrial and ventricular leads and allows for AV synchrony in patients with various types of AV block. \r\n\r\nSetting the pacemaker properly requires a series of steps. Once the appropriate mode and heart rate are set, lead capture and sensitivity thresholds should be tested. Capture threshold is the minimum current in milliamps (mA) required to induce myocardial depolarization of the paced chamber. After setting the pacemaker rate above the patient\u2019s intrinsic rate, capture threshold is found by decreasing the pacemaker output until the P wave (atrial lead) or the R wave (ventricular lead) no longer follows each pacing spike. For safety, the output is set at twice the capture threshold to a maximum of 10 mA. \r\n\r\nThe lead electrodes do not only pace, but they also sense the electrical activity of the myocardial surface. Sensitivity threshold is the minimum myocardial voltage that is detected as a P wave or R wave in millivolts (mV) by the pacemaker. If the voltage of a P wave or R wave is below the sensitivity threshold, it will not be sensed, and the pacemaker will pace at the set rate. The lower the sensitivity threshold that is set in mV, the higher is the sensitivity of the lead electrode. To determine the sensitivity threshold, the pacing rate must be temporarily set lower than patient\u2019s native rate. The sensitivity of the lead for each appropriate chamber then must be reduced by increasing the voltage (mV) until the pacemaker no longer senses any endogenous electrical activity of the myocardium and will start to pace asynchronously. Thus, a pacing spike will appear before each P wave or R wave\/QRS complex. For safety reasons, the pacemaker sensitivity should be carefully increased by decreasing the mV to about half the threshold. The general range of sensitivity for a normal pacemaker box is 0.4 to 10 mV for the atria and 0.8 to 20 mV for the ventricles. The default settings for the Medtronic pacemaker box are 0.5 mV for the atria and 2 mV for the ventricles. \r\n\r\nOther relevant pacemaker parameters include AV delay and post-ventricular atrial refractory period (PVARP). AV delay allows time for ventricular filling after atrial contraction and before ventricular contraction. If the patient\u2019s AV node intrinsically conducts more rapidly than the set AV delay, an endogenous ventricular beat may occur but if it does not, the pacemaker can pace the ventricle when set appropriately. AV interval is automatically determined with the pacemaker set rate but may be manually changed and allow for better ventricular filling, especially in the context of rapid atrial rate or diastolic dysfunction. Of note, an intrinsic ventricular beat will always provide better stroke volume and cardiac output as ventricular depolarization occurs in a more synchronized fashion versus depolarization from a right ventricular epicardial lead. Normal AV delay values range between 100 to 150 milliseconds (ms). \r\n\r\nPVARP refers to the period after which the ventricular lead delivers an electrical impulse and during which the atrial lead will not be able to sense any myocardial voltage in the atria. The goal is to prevent the atrial lead from either far-field sensing of ventricular voltage or sensing atrial voltage from retrograde depolarization via a re-entry pathway. If either are sensed by the atrial lead and therefore interpreted as atrial depolarization, the ventricular lead will then pace the ventricle and induce pacemaker-mediated tachycardia. Pacemaker-mediated tachycardia presents with a ventricular paced rate that is faster than the set pacer rate and may be terminated by prolonging the PVARP. \r\n\r\nThe rhythm tracing in the stem demonstrates complete heart block. The most appropriate pacemaker mode is DDD to allow AV synchrony with an appropriately set heart rate. AAI mode is not appropriate as there is lack of AV nodal conduction. Although VVI may be useful to increase the heart rate, it is less optimal than DDD mode as it does not provide AV synchrony. \r\n\r\n \r\nREFERENCES \r\nRobinson JA, Leclair G, Escudero CA. Pacing in Pediatric Patients with Postoperative Atrioventricular Block. Card Electrophysiol Clin<\/em>. 2023;15(4):401-411. doi: 10.1016\/j.ccep.2023.06.008\r\n\r\nReade MC. Temporary epicardial pacing after cardiac surgery: a practical review: part 1: general considerations in the management of epicardial pacing [published correction appears in Anaesthesia. 2007 Jun;62(6):644]. Anaesthesia<\/em>. 2007;62(3):264-271. doi: 10.1111\/j.1365-2044.2007.04950.x\r\n\r\nReade MC. Temporary epicardial pacing after cardiac surgery: a practical review. Part 2: Selection of epicardial pacing modes and troubleshooting. Anaesthesia<\/em>. 2007;62(4):364-373. doi: 10.1111\/j.1365-2044.2007.04951.x\r\n\r\nAndropoulos DB. Anesthesia for Congenital Heart Disease<\/em>. 2nd ed. Wiley-Blackwell; 2010. Chapter 22. \r\n\r\n”,”hint”:””,”answers”:{“uoebz”:{“id”:”uoebz”,”image”:””,”imageId”:””,”title”:”A)\tAAI”},”qavmt”:{“id”:”qavmt”,”image”:””,”imageId”:””,”title”:”B)\tDDD”,”isCorrect”:”1″},”u3y4g”:{“id”:”u3y4g”,”image”:””,”imageId”:””,”title”:”C)\tVVI”}}}}}

{“questions”:{“a2kgd”:{“id”:”a2kgd”,”mediaType”:”image”,”answerType”:”text”,”imageCredit”:””,”image”:””,”imageId”:””,”video”:””,”imagePlaceholder”:””,”imagePlaceholderId”:””,”title”:”Author: Melissa Colizza, MD – Stollery Children\u2019s Hospital – Edmonton, Alberta \r\n\r\nA 6-day-old neonate with hypoplastic left heart syndrome (HLHS) requires venoarterial extracorporeal membrane oxygenation for low cardiac output and inability to wean from cardiopulmonary bypass after a Norwood\/Sano procedure. The patient expires due to multi-system organ failure without recovery of myocardial function. Autopsy demonstrates diffuse biventricular fibroelastosis and evidence of ventriculo-coronary connections. Which of the following anatomical subtypes of HLHS is MOST likely associated with these autopsy findings?\r\n”,”desc”:”EXPLANATION \r\nThe 2021 International Paediatric and Congenital Cardiac Code (IPCCC) and the eleventh revision of the International Classification of Diseases (ICD-11) defines hypoplastic left heart syndrome (HLHS) as a \u201cspectrum of congenital cardiovascular malformations with normally related great arteries, without a common atrioventricular junction, characterized by underdevelopment of the left heart and significant hypoplasia of the left ventricle, including atresia, stenosis, or hypoplasia of the aortic or mitral valve, or both valves, and hypoplasia of the ascending aorta and aortic arch\u201d. While the etiology remains unknown, pathological studies suggest it is a disease acquired during fetal life after closure of the interventricular septum. Four anatomical subtypes have been recognized, according to the degree of obstruction of mitral inflow and aortic outflow which include mitral atresia\/aortic atresia (MA\/AA), mitral stenosis\/aortic atresia (MS\/AA), mitral stenosis \/ aortic stenosis (MS\/AS) and mitral atresia \/ aortic stenosis (MA\/AS). MA\/AA is the most common subtype, comprising approximately 35-45% of patients with HLHS. MS\/AA and MS\/AS occur at a similar incidence of 20-25%, and MA\/AS is the rarest subtype.\r\n\r\nThese subtypes also differ with regards to the shape of the left ventricle (LV), endocardial lining and myocardial perfusion. Stephens et al performed pathological examinations on 119 HLHS specimens, most of them being archived prior to the development of palliative surgical\/interventional procedures. They found that the majority of MA\/AA hearts had slit-like ventricles, the smallest aortas, and that endocardial fibroelastosis (EFE) was rare. Conversely, most MS\/AA hearts have a globular shape, and approximately 75% of them had EFE. Hearts with MS\/AS had the most variable anatomy with very few having a slit-like LV, approximately half with a globular LV shape, and some with LVs that could qualify as HLHS \u201ccomplex\u201d, meaning the LV size is proportional to the valvar opening and could be considered for a biventricular repair. Interestingly, almost 75% of MS\/AS hearts had EFE. An additional study from Stephens et al reported described the coronary anatomy of the same patient cohort, and noted that MS\/AS hearts had more frequent anomalies of coronary artery position with greater potential for coronary obstruction, but that fistulous connections were significantly more frequent in MS\/AA hearts. \r\n\r\nFrom a clinical standpoint, interstage mortality after the Norwood operation is estimated at 10-15%. Studies from 2000 to 2010 have reported a significantly higher mortality rate in patients with MS\/AA when compared to the other subtypes. The hypothesis behind that is HLHS patients with mitral stenosis have larger LV cavities, thus higher left ventricular end diatolic pressure (LVEDP), and a higher incidence of ventriculo-coronary connections, increasing the risk of myocardial ischemia, especially during cardiopulmonary bypass when the ventricle is decompressed. \r\n\r\nA retrospective study by Siehr et al comparing perioperative mortality of MS\/AA to all other subtypes of HLHS reported a perioperative mortality rate of 29% versus 7%, respectively, after the Stage I procedure. Eight of fourteen MS\/AA patients had coronary angiography, and six were found to have ventriculo-coronary connections. Four of the six with fistulous connections died. Rickers et al performed cardiac magnetic resonance imaging (cMRI) studies to quantify coronary blood flow and determine factors affecting the coronary microcirculation in all four types of HLHLS patients after the Fontan procedure. Myocardial blood flow was quantified at rest and during adenosine-induced hyperemia. They demonstrated that systemic right ventricular (RV) hyperemic myocardial blood flow, which depends on ventricular capillarization and coronary vasoreactivity, was decreased in patients with MS\/AA, RV diastolic dysfunction, and those who had their Fontan at a later age. Moon et al analyzed long-term outcomes in HLHS patients, and found that patients with MS\/AA had decreased transplant-free survival at 15 years (68%) versus those with MS\/AS (84%) or MA\/AA (79%). MS\/AA patients were also more likely to have ventricular failure. Aortic atresia (AA) is also a known risk factor for mortality after the Norwood procedure, especially in patients with aortic diameters less than 1.5mm, which may reflect the technical challenges of the surgery as well as retrograde coronary blood flow. \r\n\r\nThus, HLHS prognosis varies according to subtype. With globular-shaped and EFE-lined LVs, patients with MS\/AA have worsened outcomes versus patients with MS\/AS. Patients with MA\/AA do not share those pathologic characteristics, nor the same mortality as MS\/AA after the Stage I procedure. In patients with MS\/AA, the combination higher LVEDP, ventricular sinusoids, and ventriculo-coronary connections increases the risk of myocardial ischemia and could be a likely explanation for these findings. The presence of a rudimentary LV could also lead to unfavorable RV-LV interactions, impaired diastolic function of the RV leading to compromised coronary blood flow, and contribute to the long-term systemic RV failure. The MA\/AS subtype remains rare and is often grouped with MS\/AS patients in studies. \r\n\r\n \r\n \r\nREFERENCES \r\nStephens EH, Gupta D, Bleiweis M, Backer CL, Anderson RH, Spicer DE. Pathologic Characteristics of 119 Archived Specimens Showing the Phenotypic Features of Hypoplastic Left Heart Syndrome. Semin Thorac Cardiovasc Surg<\/em>. 2020;32(4):895-903. doi: 10.1053\/j.semtcvs.2020.02.019 \r\n\r\n\r\nStephens EH, Gupta D, Bleiweis M, Backer CL, Anderson RH, Spicer DE. Coronary Arterial Abnormalities in Hypoplastic Left Heart Syndrome: Pathologic Characteristics of Archived Specimens. Semin Thorac Cardiovasc Surg<\/em>. 2020;32(3):531-538. doi: 10.1053\/j.semtcvs.2020.02.007\r\n\r\n\r\nSiehr SL, Maeda K, Connolly AA, et al. Mitral Stenosis and Aortic Atresia–A Risk Factor for Mortality After the Modified Norwood Operation in Hypoplastic Left Heart Syndrome. Ann Thorac Surg<\/em>. 2016;101(1):162-167. doi: 10.1016\/j.athoracsur.2015.09.056\r\n\r\n\r\nRickers C, Wegner P, Silberbach M, et al. Myocardial Perfusion in Hypoplastic Left Heart Syndrome. Circ Cardiovasc Imaging<\/em>. 2021;14(10):e012468. DOI: 10.1161\/CIRCIMAGING.121.012468\r\n\r\n\r\nMoon J, Lancaster T, Sood V, Si MS, Ohye RG, Romano JC. Long-term impact of anatomic subtype in hypoplastic left heart syndrome after Fontan completion. J Thorac Cardiovasc Surg<\/em>. Published online November 10, 2023. doi: 10.1016\/j.jtcvs.2023.11.008\r\n\r\n”,”hint”:””,”answers”:{“9foxh”:{“id”:”9foxh”,”image”:””,”imageId”:””,”title”:”A)\tMitral atresia \u2013 Aortic atresia”},”n69qs”:{“id”:”n69qs”,”image”:””,”imageId”:””,”title”:”B)\tMitral stenosis \u2013 Aortic atresia “,”isCorrect”:”1″},”rwg7h”:{“id”:”rwg7h”,”image”:””,”imageId”:””,”title”:”C)\tMitral stenosis \u2013 Aortic stenosis”}}}}}

{“questions”:{“oilcg”:{“id”:”oilcg”,”mediaType”:”image”,”answerType”:”text”,”imageCredit”:””,”image”:””,”imageId”:””,”video”:””,”imagePlaceholder”:””,”imagePlaceholderId”:””,”title”:”Authors: Meera Gangadharan, MBBS, FAAP, FASA – Childrens Memorial Hermann Hospital\/McGovern Medical School, Houston, TX and Destiny F. Chau, MD Arkansas Children\u2019s Hospital\/ University of Arkansas for Medical Sciences, Little Rock, AR \r\n\r\nA 17-year-old male with a history of hypertrophic cardiomyopathy and an implantable cardiac defibrillator presents for cardiac magnetic resonance imaging. The device is classified as MR conditional. According to the Heart Rhythm Society\u2019s expert consensus statement on magnetic resonance imaging in patients with cardiac implantable electronic devices, which of the following recommendations is MOST appropriate during the MRI scan?\r\n\r\n\r\n”,”desc”:”EXPLANATION \r\nPatients with cardiac implantable electronic devices (CIEDs) must undergo safety screening for their CIED prior to magnetic resonance imaging (MRI). The screening process includes an evaluation of the device and the predicted performance in the MRI environment. The CIED is then classified as one of the following: a) \u201cMR safe\u201d – no hazard in any MR environments, b) \u201cMR unsafe\u201d – an object known to pose hazards in all MR environments, and c) \u201cMR conditional\u201d- an object in a specified MRI environment within specified conditions that does not pose a known hazard. CIEDs that do not meet the criteria to be MR conditional have a designation of a \u201cMR nonconditional system\u201d. This includes MR conditional generators that are combined with nonconditional leads.\r\n\r\n\r\nAlthough there are currently no CIEDs with MR safe designation, several modern CIED systems are designated MR conditional by the Food and Drug administration (FDA). The development of MR Conditional CIED devices has involved modifications of the generator, leads, and\/or MRI scan field conditions. Field conditions include the body sector for imaging, MRI operating criteria, lead and generator combination, and mode of programming, all of which can vary among manufacturers and specific devices. \r\n\r\n\r\nAlthough the physics of MR imaging is extremely complex, it is helpful to understand how the scan is generated. To produce an MR image requires the application of a static magnetic field to align protons with or against the magnetic field, a source of radiofrequency (RF) pulsed waves to excite the nuclear spin of protons which causes an energy transition, and magnetic field gradients to localize the signal in space that is emitted after the RF signal is turned off. Pulse sequences are generated by applying a series of RF pulses to the anatomy of interest. The parameters of the pulse sequence(s) can be varied to generate contrast between tissues, based on the relaxation properties of hydrogen nuclei. These various electromagnetic fields, either alone or in combination, can interact with some ferromagnetic materials or damage sensitive electronic components of the device. Adverse effects of the MRI electromagnetic field on CIEDs include:\r\n\r\n\r\n1.\tTorque and movement due to ferromagnetic materials. Generally, CIED generator movement is unlikely due to subcutaneous tissue encasing, especially six weeks and longer after initial CIED placement. Newer generators and leads are made with titanium and its alloys with limited ferromagnetic materials, making movement an unlikely event. \r\n2.\tElectrical current induction by pulsed RF and gradient magnetic field. Low frequency electrial currents can be induced in leads within the field. In pacemakers (PMs), this can result in inhibition, leading to asynchronous pacing or overdrive pacing due to perceived cardiac electrical activity. In implanted cardiac defibrillators (ICDs), the consequences include inappropriate inhibition or induction of anti-tachycardia pacing or inappropriate shock delivery when a rapidly changing gradient electromagnetic field is interpreted as native cardiac activity. Newer CIEDs contain improved band pass filters, programming, and shielding to reduce background noise. \r\n3.\tTissue damage from heat generation. Radiofrequency fields can induce heating in the nonconditional components of the device, leading to tissue damage from heat generation and device malfunction. Lead sensing and capture thresholds may also become altered due to tissue damage near lead electrodes (termed functional ablation). \r\nThe decision to perform MRI on a patient with a CIED requires a detailed assessment of the risks versus benefits of the scan. The determination of MR conditional status requires knowledge of the device specifics, presence of abandoned or fractured leads, location of device components, and manufacturers of the device components. Although some current CIED systems have been FDA-approved for the 3 Tesla magnet, most of the MRI safety literature is based on scans performed in \u201cnormal operating mode using the 1.5 Tesla magnet. \r\n\r\nDue to the variety of CIED systems and patient characteristics, an individualized approach is necessary to ensure safety and provide the optimal conditions to obtain the best diagnostic information from the scan. Recommendations by the Heart Rhythm Society (2017) for the management of patients with MR conditional CIED systems who undergo MRI include the following: \r\n\r\n1)\tMR conditional devices should adhere to the product instructions, which includes programming the appropriate \u201cMR mode\u201d and scanning within the prerequisites specified for the device. The MR mode features include prescan system integrity checks, asynchronous pacing or nonstimulation modes (nonsensing modes), disabling of tachycardia detection, increased output during the scan, and restoration of prescan states and values. \r\n2)\tA rigourous standardized institutional protocol specific for MR imaging in these patients should always be applied. Such protocols should include the benefits assessment of MRI versus alternative diagnostic methods, pre-MRI and post-MRI device evaluation, and appropriate MR conditional device programming specific to the CIED and patient characteristics. A protocol checklist should be used, preferably one that would be traceable in the electronic system.\r\n3)\tSkilled personnel to perform advanced cardiac life support, arrhythmia recognition, defibrillation, and transcutaneous pacing are recommended to be in attendance with the patient during the time period when the device is reprogrammed until returned to baseline. The institutional protocol should specify whether this is nursing or medical staff. \r\n4)\tMR-safe ECG and pulse oximetry monitoring is recommended during the time of MR-mode programming and continued until baseline or other clinically appropriate CIED settings are restored. Pulse oximetry is particularly useful, as it is less prone to electromagnetic interference when compared to the ECG. \r\n5)\tResuscitative efforts involving the use of a defibrillator\/monitor, device programming system, or any other MR- unsafe equipment should be performed after moving the patient outside of Zone 4 and into a nearby designated magnetically safe area. \r\n6)\tPersonnel with the skills to program the CIED need to be available as defined by an institutional protocol. Such personnel are generally not required to be present during the scan. \r\n7)\tBased on the risk and benefit to the patient, it is reasonable to perform an MRI scan earlier than the exempt period for conditionality of the system. \r\nBased on these recommendations, the patient in the scenario should be managed as follows: (1) the ICD should be programmed to \u201cMRI-mode\u201d according to device instructions; (2) trained staff skilled to perform advanced cardiac life support, arrhythmia recognition, defibrillation, and transcutaneous pacing should be in attendance with the patient during the time period the device is reprogrammed, until returned to baseline; (3) vital signs monitoring in the form of ECG and pulse oximetry should be used until the patient\u2019s device settings are restored back to baseline. \r\n\r\n\r\nThe Heart Rhythm Society\u2019s expert consensus statement makes a special mention of CIEDs in adults and children with congenital heart disease. Often patients with congenital heart defects have CIEDs placed at a very young age. Infants and small children usually have epicardial leads and abdominal generators. These patients typically require multiple CIED revisions over the course of their lifetime and may have abandoned leads in situ. These combinations of current and abandoned leads and generators often render the system to be MR nonconditional. However, a MR nonconditional device does not preclude a MRI but does necessitate additional precautions. These include obtaining written consent, checking the device before and after the MRI, and the presence of personnel with the skills to recognize arrhythmias and abililty to provide cardiopulmonary resuscitation and transcutaneous pacing until device settings are restored. \r\n\r\nThe European Association of Cardiovascular Imaging and the Heart Rhythm Society emphasize that the presence of a CIED should not deny a patient the benefit of MRI. Instead, the decision to perform an MRI should be made thoughtfully and collaboratively, with robust institutional protocols in place to maximize the probability of safe outcomes. \r\n\r\n\r\n \r\nREFERENCES \r\n\r\nIndik JH, Gimbel JR, Abe H, et al. 2017 HRS expert consensus statement on magnetic resonance imaging and radiation exposure in patients with cardiovascular implantable electronic devices. Heart Rhythm<\/em>. 2017;14(7):e97-e153. doi:10.1016\/j.hrthm.2017.04.025\r\n\r\n\r\nStankovic I, Voigt JU, Burri H, et al. Imaging in patients with cardiovascular implantable electronic devices: part 2-imaging after device implantation. A clinical consensus statement of the European Association of Cardiovascular Imaging (EACVI) and the European Heart Rhythm Association (EHRA) of the ESC. Eur Heart J Cardiovasc Imaging<\/em>. 2023;25(1):e33-e54. doi:10.1093\/ehjci\/jead273\r\n\r\n”,”hint”:””,”answers”:{“mwjnj”:{“id”:”mwjnj”,”image”:””,”imageId”:””,”title”:”A)\tContinue current device settings without reprograming the mode.”},”1s07x”:{“id”:”1s07x”,”image”:””,”imageId”:””,”title”:”B)\tMonitor with continuous ECG only.”},”cysgx”:{“id”:”cysgx”,”image”:””,”imageId”:””,”title”:”C)\tPersonnel trained in advanced cardiac life support must be in attendance. “,”isCorrect”:”1″}}}}}

{“questions”:{“antwf”:{“id”:”antwf”,”mediaType”:”image”,”answerType”:”text”,”imageCredit”:””,”image”:””,”imageId”:””,”video”:””,”imagePlaceholder”:””,”imagePlaceholderId”:””,”title”:”Authors: Meera Gangadharan, MBBS, FAAP, FASA – Children\u2019s Memorial Hermann Hospital\/McGovern Medical School, Houston, TX and Destiny F. Chau, MD – Arkansas Children\u2019s Hospital\/ University of Arkansas for Medical Sciences, Little Rock, AR \r\n\r\nA 10-year-old patient with an extra-cardiac Fontan is undergoing a cardiac catheterization to evaluate recent-onset shortness of breath and productive cough. Shortly after endotracheal intubation, the peak airway pressure is 40 cm H_{2<\/sub>O along with diminished bilateral breath sounds and decreasing end tidal CO2<\/sub> on capnography. The systemic oxygen saturation falls from 83% to 68% with no response to albuterol or intravenous epinephrine. Which of the following diagnoses is the MOST likely etiology for this clinical scenario?\r\n”,”desc”:”EXPLANATION \r\n\r\nThe Fontan circulation is characterized by a high central venous pressure necessary to drive blood through the pulmonary vascular bed in the absence of a subpulmonary ventricle. At the level of the capillary bed this imposes greater demands on the lymphatic system to clear fluid from the interstitial tissue. Lymphatic capillaries are thin-walled vessels that connect to larger vessels called lymphangions, which propel lymph toward the lymph nodes and eventually to the thoracic duct or the right lymphatic duct. (See Figure 1) \r\n \r\n\r\nFigure 1. Anatomy of lymphatic vascular system. (From Ahmed MA. Creative Commons Attribution License CC-BY 4.0.) \r\n\r\nChronically high central venous pressures, typical of the Fontan circulation, causes increased production of lymphatic fluid by the liver. As a result, lymphatic vessels dilate to accommodate changes in capillary bed filtration. Lymphatic congestion with subsequent lymphatic fluid leak results in downstream pleural fluid accumulation, plastic bronchitis, ascites, and protein losing enteropathy. \r\n\r\nApproximately 5% of Fontan patients develop plastic bronchitis, a condition characterized by the exudation of protein-rich lymphatic fluid into the bronchial airways with the formation of casts. The casts are typically described as having a rubber-like consistency and taking the shape of the containing airways (See Figure 2). Casts are thought to develop from the crosslinking of fibrin within the lymphatic fluid contained in the airways and may lead to complete airway obstruction. Patients may present with wheezing, dyspnea, pleuritic chest pain, fever, hypoxia, and a cough productive of casts. In addition to Fontan patients, plastic bronchitis has also been reported in patients with asthma, sickle cell disease, infectious and allergic conditions, cystic fibrosis and lymphatic malformations.\r\n \r\n\r\nFigure 2. Bronchial cast. (From Pa\u0142yga-Bysiecka et al. Creative commons attribution license (https:\/\/ creativecommons.org\/licenses\/by\/ 4.0\/) \r\n\r\nTreatment consists of facilitating the physical removal of bronchial casts by expectoration or bronchoscopy. Inhaled bronchodilators, N-acetylcysteine, dornase alpha, DNase, inhaled heparin, and tissue plasminogen activator are prescribed to facilitate expectoration. Corticosteroids may be administered to reduce inflammation, a possible contributing factor. Interventions to reduce the extravasation of lymphatic fluid include: 1) intervention\/treatment to reduce Fontan pressure and, 2) MRI-guided lymphangiography with lymphatic vessel interventions to disrupt communications with the airway. Fontan patients are typically evaluated for physical obstruction within the Fontan pathway and high pulmonary vascular resistance, both of which impede blood flow and increase upstream pressure. Targeted interventions may include creating or enlarging a Fontan fenestration, relieving physical obstruction with stents or balloon angioplasty, or medical treatment with pulmonary vasodilators. Furthermore, patients with severe valvular regurgitation may necessitate valve repair\/replacement. Likewise, the presence of arrhythmias may require cardiac resynchronization and anti-arrhythmic medications. Refractory Fontan failure can lead to Fontan take-down or heart transplantation. \r\n\r\n\r\nAnesthetic management for bronchoscopy and removal of airway casts can be fraught with complications. Singhal et al describe the periprocedural course of two pediatric patients with Fontan physiology who developed hemodynamic instability, hypoxemia and hypercarbia during bronchoscopy for removal of bronchial casts. One patient was managed with multiple vasoactive agents and stress-dose steroids due the development of septic shock while the second patient required veno-arterial extracorporeal membrane oxygenation due to cardiorespiratory failure. \r\n\r\n\r\nThe patient described in the stem presents with respiratory distress and productive cough. After intubation, high peak airway pressures and decreased oxygen saturation may be due to any of the answer choices. However, tension pneumothorax is doubtful given the presence of bilateral breath sounds. Further, the patient is unresponsive to treatment with albuterol and epinephrine, making bronchospasm unlikely. Given the known complications of Fontan physiology and the clinical presentation, this patient most likely has plastic bronchitis and major airway obstruction from bronchial casts. \r\n\r\n \r\nREFERENCES\r\n\r\nPa\u0142yga-Bysiecka I, Polewczyk AM, Polewczyk M, Ko\u0142odziej E, Mazurek H, Pogorzelski A. Plastic bronchitis-A serious rare complication affecting children only after Fontan procedure? J Clin Med<\/em>. 2021; 11(1):44. doi:10.3390\/jcm110100\r\n\r\n\r\nRychik J, Atz AM, Celermajer DS, et al. Evaluation and management of the child and adult with Fontan circulation: A scientific statement from the American Heart Association. Circulation<\/em>. 2019; 140(6):e234-e284.\r\n\r\n\r\nLi Y, Williams RJ, Dombrowski ND, et al. Current evaluation and management of plastic bronchitis in the pediatric population. Int J Pediatr Otorhinolaryngol<\/em>. 2020; 130:109799. doi:10.1016\/j.ijporl.2019.109799\r\n\r\n\r\nSinghal NR, Da Cruz EM, Nicolarsen J, et al. Perioperative management of shock in two Fontan patients with plastic bronchitis. Semin Cardiothorac Vasc Anesth<\/em>. 2013; 17(1):55-60. doi:10.1177\/1089253213475879\r\n\r\n\r\nAhmed MA Sr. Post-operative chylothorax in children undergoing congenital heart surgery. Cureus<\/em>. 2021; 13(3):e13811. doi:10.7759\/cureus.13811\r\n”,”hint”:””,”answers”:{“kgfl8”:{“id”:”kgfl8″,”image”:””,”imageId”:””,”title”:”A. Bronchospasm”},”5kjxr”:{“id”:”5kjxr”,”image”:””,”imageId”:””,”title”:”B. Airway obstruction with bronchial casts”,”isCorrect”:”1″},”xjzmz”:{“id”:”xjzmz”,”image”:””,”imageId”:””,”title”:”C. Tension pneumothorax”}}}}}}