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

{“questions”:{“phvb5”:{“id”:”phvb5″,”mediaType”:”image”,”answerType”:”text”,”imageCredit”:””,”image”:””,”imageId”:””,”video”:””,”imagePlaceholder”:””,”imagePlaceholderId”:””,”title”:”Author: Nicholas Houska, DO – University of Colorado – Children\u2019s Hospital Colorado\r\n\r\nA six-week-old infant with a history of congenital central hypoventilation syndrome (CCHS) presents for an exam under anesthesia and rectal biopsy for suspected Hirschsprung\u2019s disease. Which of the following cardiac arrhythmias is MOST likely to be coexistent in this patient?\r\n”,”desc”:”EXPLANATION \r\nCongenital central hypoventilation syndrome (CCHS), or \u201cOndines curse\u201d, is an abnormality in the autonomic regulation of ventilation by the central nervous system not explained by any pulmonary, neurological, or muscular disorders. This results in a reduced or absent ventilatory response to hypercapnia and hypoxia, as well as other autonomic disorders.\r\n\r\n\r\nThe main presenting symptom of CCHS is acute or chronic hypoventilation. Depending on the phenotype, this may present as a neonate, infant, or less commonly later in life. Other conditions associated with CCHS include: Hirschsprung disease, neural crest tumors, esophageal dysmotility, and cardiac arrythmias. \r\n\r\n\r\nIn 2003, mutations in the PHOX2B gene were identified as the major genetic cause of CCHS. These mutations have further been classified as polyalanine repeat mutations (PARMs), or less commonly, non-PARMs. These genotypes have been found to exhibit different phenotypes of CCHS, each with varying onset, degrees of hypoventilation, and other autonomic disorders as mentioned in the previous paragraph. Transmission of the PHOX2B mutation is autosomal dominant, with a 50% risk of transmission to offspring. \r\n\r\n\r\nDiagnosis is based on clinical signs and symptoms, exclusion of other causes of hypoventilation, and polysomnography which typically shows hypoventilation, worse while sleeping than awake, and most severe during non-rapid eye movement sleep. Concern for signs, symptoms, and other known manifestations of CCHS should prompt genetic testing for mutations of the PHOXB gene. \r\n\r\n\r\nThere is no pharmacologic management for the ventilatory symptoms of CCHS, and lifelong ventilatory support will be required for these patients. Depending on phenotype, this ventilatory support may be required only while asleep or 24 hours a day. Ventilation strategies may be non-invasive or invasive ventilation via tracheostomy, particularly in children. Support options include positive pressure ventilation, mask ventilation, and diaphragm pacing via phrenic nerve stimulation. The anesthesiologist caring for these children should be aware that even patients requiring nighttime ventilatory support only will often exhibit increased hypoventilation due to the effects of anesthesia. Preparation should be made for extended monitoring and ventilatory support in the perioperative period. \r\n\r\n\r\nPatients with CCHS often exhibit cardiac arrythmias, typically sinus node dysfunction, sinus pauses, bradycardia, and prolonged R-R intervals. Manifestations of this autonomic dysfunction include syncope, postural hypotension, nocturnal hypertension, and increased risk of sudden death. Patients should be monitored with an annual ECG Holter monitor. Syncope should warrant extended Holter monitoring and\/or consideration of pacemaker implantation. The current recommendation for CCHS patients is to follow the ACC\/AHA guidelines for pacemaker placement. These guidelines recommend pacemaker placement for patients with R-R interval >3 seconds and recurrent syncopal episodes. Typically, a single chamber atrial pacemaker is sufficient. However, a dual-chamber device may be preferable due to the subsequent possibility of developing atrioventricular block. Patients with phrenic nerve pacers require special attention during pacemaker implantation to not cause cross interference between devices. In these patients, the cardiac pacemaker lead should be bipolar to avoid interference with the phenic nerve pacer.\r\n\r\n\r\nFor the patient in the stem, the most likely arrhythmia is sick sinus syndrome due to a known association of CCHS with sinus node dysfunction. Supraventricular tachycardias and ectopic atrial tachycardia are not commonly associated with CCHS.\r\n\r\n \r\nREFERENCES \r\n\r\nTrang H, Samuels M, Ceccherini I, et al. Guidelines for diagnosis and management of congenital central hypoventilation syndrome.Orphanet J Rare Dis<\/em>. 2020;15(1):252.\r\n\r\n\r\nGronli JO, Santucci BA, Leurgans SE, Berry-Kravis EM, Weese-Mayer DE. Congenital central hypoventilation syndrome: PHOX2B<\/em> genotype determines risk for sudden death. Pediatr Pulmonol<\/em>. 2008; 43(1): 77-86. \r\n\r\n\r\nWeese-Mayer DE, Rand CM, Khaytin I, et al. Congenital Central Hypoventilation Syndrome. 2004 Jan 28 [Updated 2021 Jan 28]. In: Adam MP, Feldman J, Mirzaa GM, et al., editors. GeneReviews\u00ae [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2024. Available from: https:\/\/www.ncbi.nlm.nih.gov\/books\/NBK1427\/\r\n”,”hint”:””,”answers”:{“dbbdo”:{“id”:”dbbdo”,”image”:””,”imageId”:””,”title”:”A. Supraventricular tachycardia “},”53kdl”:{“id”:”53kdl”,”image”:””,”imageId”:””,”title”:”B. Sick sinus syndrome”,”isCorrect”:”1″},”ujv5y”:{“id”:”ujv5y”,”image”:””,”imageId”:””,”title”:”C. Ectopic atrial tachycardia”}}}}}

{“questions”:{“3q03h”:{“id”:”3q03h”,”mediaType”:”image”,”answerType”:”text”,”imageCredit”:””,”image”:””,”imageId”:””,”video”:””,”imagePlaceholder”:””,”imagePlaceholderId”:””,”title”:”Author: Melissa Colizza – Stollery Children\u2019s Hospital – Edmonton, Canada \r\nAccording to a retrospective analysis by Saengsin et al. from the November 2023 issue of Anesthesia and Analgesia, that compared patients who received milrinone to matched cohorts who did not receive milrinone after Tetralogy of Fallot repair, which of the following outcomes was MOST likely to be observed during the first 72 hours after surgery in patients who received milrinone? \r\n”,”desc”:”EXPLANATION \r\nLow cardiac output syndrome (LCOS) is a common occurrence in the pediatric cardiac surgical population, with an incidence of 25%-60% reported in the literature. LCOS is a clinical syndrome in which there is an imbalance of oxygen supply and demand to the tissues. Prevention and management often necessitate the use of both pharmacologic and nonpharmacologic strategies to restore oxygen balance. The etiology of post-surgical LCOS is multifactorial, including myocardial ischemia during aortic cross clamping, the effects of cardioplegia, activation of the inflammatory and complement cascades and changes in pulmonary and\/or systemic vascular resistance. It is associated with a decrease in cardiac index, accompanied by an increase in systemic vascular resistance (SVR) and pulmonary vascular resistance (PVR). Risk factors include younger age (especially neonates), complex procedures with prolonged cardiopulmonary bypass times, use of large patch materials for repair, and ventriculotomies.\r\n\r\n\r\nMilrinone is a phosphodiesterase-3 (PDE-3) inhibitor with vasodilatory and inotropic properties. The Prophylactic Intravenous use of Milrinone After Cardiac Operation in Pediatrics \r\n(PRIMACORP) study by Hoffman et al (2003) is a landmark study, as it highlighted the importance of LCOS prevention. The study compared mortality and the development of LCOS (requiring additional pharmacological or other support) within in the first 36 hours after treatment in three groups of patients under six years old following biventricular repair. Patients were randomly assigned to three groups, a high-dose milrinone (75mcg\/kg loading dose with an infusion at 0.75 mcg\/kg\/min), a low-dose milrinone (25mcg\/kg loading dose with an infusion at 0.25 mcg\/kg\/min), or placebo treatment group. LCOS was defined as clinical signs or symptoms of hypoperfusion, with or without a widened arterio-venous oxygen saturation (AVO_{2<\/sub>) difference or metabolic acidosis. The trial showed a relative risk reduction of 64% for LCOS in the high dose milrinone group when compared to placebo. It also revealed a 5-9% decrease in systolic blood pressure after milrinone loading dose administration. Notably, this trial advanced the use of milrinone as an alternative or adjuvant to other vasoactive agents and has led to its widespread use after pediatric cardiac surgery. \r\n\r\n\r\nDespite the results of the PRIMACORP study, strategies to prevent and treat LCOS vary widely. While many centers start milrinone intra-operatively and continue post-operatively, dosage and timing of administration differs greatly. Interestingly, milrinone dosage is often lower than that used in the PRIMACORP study, and it is frequently co-administered with other vasoactive agents. A 2015 Cochrane review by Burkhardt et al examined five randomized-controlled trials comparing milrinone to either placebo, levosimendan, or dobutamine. The authors concluded that milrinone could reduce incidence of LCOS versus placebo in the short-term (up to 36 hours), but that there is insufficient evidence to suggest its effectiveness in preventing mortality or LCOS in the pediatric cardiac surgical population, especially when compared to other agents. \r\n\r\n\r\n\r\nA retrospective study from Boston Children\u2019s Hospital by Mills et al (2016) investigated the use of milrinone to reduce SVR in neonates undergoing Stage 1 palliation for hypoplastic left heart syndrome (HLHS). Patients were administered a loading dose of milrinone (25 to 100 mcg\/kg titrated to goal SVR at a cardiac index of 2 L\/min m^{2<\/sup>) prior to weaning from cardiopulmonary bypass and an infusion of milrinone (0.25 to 1 mcg\/kg\/min) upon separation from cardiopulmonary bypass (CPB) which was continued in the cardiac intensive care unit (CICU). Epinephrine was used as the main inotropic agent. The study demonstrated that the milrinone-treated group, after correction for shorter CPB times, had lower SVR, decreased AV-O2<\/sub> difference and lower lactate levels. This study highlights the physiologic impact of high SVR on the parallel, single-ventricle circulation by demonstrating that lower SVR in conjunction with adequate inotropy leads to improved oxygen delivery (DO2<\/sub>) and is beneficial in this patient population. \r\n\r\n\r\nMore recently, Saengsin et al investigated milrinone use in children less than one year of age undergoing complete Tetralogy of Fallot (TOF) repair. The study included patients with classic TOF or TOF with pulmonary atresia (without major aortopulmonary collateral arteries) between September 2011 and January 2020. Propensity scoring was used to match 212 patients based on anatomical and surgical risks (106 milrinone-treated versus 106 non milrinone-treated). The primary outcome measure was the need for administration of volume (blood products and 5% albumin) during the first 72 hours after surgery. Secondary outcomes included vital signs (heart rate and blood pressure) and indices of cardiac output and oxygen delivery. The dose and timing of milrinone administration were not protocolized. Milrinone-treated patients tended to be younger with lower weights and smaller tricuspid valves, pulmonary valves and main pulmonary arteries, and were more frequently repaired with transannular patches. The study demonstrated that patients treated with milrinone received more fluid boluses than those who did not (66% vs 52%; confidence interval 1%-27%, P=0.036). In addition, the total volume administered during the first 72 postoperative hours was significantly associated with the total amount of milrinone administered. There was no difference in perfusion indices, such as AVO2<\/sub> difference or serum lactates, nor in ICU or hospital lengths of stay. This study has several limitations. In addition to being a single-center, retrospective study, the dosing of milrinone was not protocolized, and surgeries occurred over a nine-year period when perioperative management strategies may have changed. However, it does provide some physiological insights into the altered physiology after surgical repair of TOF. The right ventricle (RV) in TOF is restrictive due to hypertrophy, use of patch material, a ventriculotomy incision and myocardial edema, which limit its capacitance due to diastolic dysfunction. In turn, this limits RV preload and cardiac output. The restrictive RV requires higher filling pressures to maintain an adequate stroke volume. The vasodilatory properties of milrinone may be counterproductive in this setting, and thus, may lead to an increased need for fluid administration. \r\n\r\n\r\nThe available evidence suggests that neonates undergoing the Stage I palliation are most likely to benefit from milrinone, especially if used with an additional inotrope to target appropriate perfusion indices. Milrinone should be used with caution in patients undergoing TOF repair due to the risk of reducing RV preload or stroke volume and thus cardiac output. There are advantages and drawbacks to each vasoactive agent and usage should be individualized to each patient\u2019s unique physiology with the goal of adequate end organ perfusion.\r\n\r\n\r\nIn summary, based on a recent retrospective study of milrinone use after TOF repair, these patients may be more likely to require increased fluid administration in the early post-operative period. However, milrinone did not appear to improve indices of cardiac output or reduce the length of stay in the intensive care unit.\r\n\r\n\r\n\r\n \r\nREFERENCES \r\nHoffman TM, Wernovsky G, Atz AM, et al. Efficacy and safety of milrinone in preventing low cardiac output syndrome in infants and children after corrective surgery for congenital heart disease. Circulation<\/em>. 2003;107(7):996-1002. doi: 10.1161\/01.cir.0000051365.81920.28\r\n\r\nBurkhardt BE, R\u00fccker G, Stiller B. Prophylactic milrinone for the prevention of low cardiac output syndrome and mortality in children undergoing surgery for congenital heart disease. Cochrane Database Syst Rev<\/em>. 2015;(3):CD009515. doi:10.1002\/14651858.CD009515.pub2\r\n\r\nMills KI, Kaza AK, Walsh BK, et al. Phosphodiesterase Inhibitor-Based Vasodilation Improves Oxygen Delivery and Clinical Outcomes Following Stage 1 Palliation. J Am Heart Assoc<\/em>. 2016;5(11): e003554. doi: 10.1161\/JAHA.116.003554\r\n\r\nSaengsin K, Sperotto F, Lu M, et al. Administration of Milrinone Following Tetralogy of Fallot Repair Increases Postoperative Volume Administration Without Improving Cardiac Output. Anesth Analg<\/em>. 2023;137(5):1056-1065. doi: 10.1213\/ANE.0000000000006662\r\n\r\nBojan M, Pouard P. Hemodynamic Management. In Andropoulos DB. Anesthesia for Congenital Heart Disease<\/em>. 4th ed. USA: Wiley-Blackwell; 2023: 494-526.\r\n\r\n”,”hint”:””,”answers”:{“ba9uw”:{“id”:”ba9uw”,”image”:””,”imageId”:””,”title”:”A. Improved indices of cardiac output”},”qrjiw”:{“id”:”qrjiw”,”image”:””,”imageId”:””,”title”:”B. Decreased intensive care unit length of stay”},”5itwm”:{“id”:”5itwm”,”image”:””,”imageId”:””,”title”:”C. Increased need for fluid resuscitation”,”isCorrect”:”1″}}}}}}}

{“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”}}}}}