EXPLANATION


Adequate myocardial protection during periods of cardiac arrest and myocardial ischemia while on cardiopulmonary bypass (CPB) is of paramount importance for good outcomes after cardiac surgery. Poor myocardial protection can lead to irreversible myocardial damage from ischemia and has been is associated with increased postoperative morbidity and mortality.


The principles of myocardial protection center on maximally reducing metabolic rate, supporting aerobic and anaerobic metabolism, preserving intracellular pH, and minimizing intracellular metabolic injury due to sodium, calcium, and oxygen free-radical accumulation. Visible end-points of myocardial protection are mechanical cardiac arrest, lack of electrical activity on the ECG and hypothermic core body temperature. Cardioplegia solutions for myocardial protection have been researched for over 40 years. Currently, there are a number of cardioplegia solutions with variable compositions, ranging from commercial to customized institutional solutions. They can be broadly classified as crystalloid cardioplegia or blood- cardioplegia depending upon the addition of blood to the cardioplegia solution. Additionally, techniques and protocols for the administration of cardioplegia vary widely depending on the patient population, surgical procedure, surgeon preference and institutional factors. Cardioplegia dose is dependent upon the particular cardioplegia formulation and the expected time of myocardial arrest. Limiting the total number and frequency of repeated cardioplegia doses is desired to reduce overall manipulation of the heart, reduce the aortic cross-clamp time and prevent myocardial edema.


A common characteristic of cardioplegia solutions is high potassium concentration in order to induce contractile arrest through membrane hyperpolarization. Components such as magnesium, mannitol, sodium bicarbonate, and lidocaine are present in cardioplegia for a number of reasons. Lidocaine is a sodium channel blocker and antiarrhythmic. Sodium channel blockage increases myocyte refractory time. Additionally, sodium channel blockage helps to counteract the negative impact of hyperkalemic arrest by polarizing the cell membrane and preventing intracellular sodium and calcium accumulation. Magnesium is a natural calcium channel blocker and reduces the accumulation of intracellular calcium. Low intracellular calcium concentrations have been associated with reduced myocardial injury. Sodium bicarbonate is a buffer which scavenges excess hydrogen ions and assists with maintaining intracellular pH. Hyperosmotic mannitol scavenges free radicals and reduces myocardial swelling. The addition of red blood cells to cardioplegia has been shown to preserve myocardial metabolism and function, resulting in less metabolic ischemic stress and reperfusion injury when compared to crystalloid-cardioplegia. In addition, red blood cells contain carbonic anhydrase, an enzyme that facilitates the scavenging of hydrogen ions to generate carbon dioxide and water.


A survey of the utilization of cardioplegia solutions by congenital cardiac surgical programs in North America found that blood-based cardioplegia formulations are predominantly used by 86% of respondents. Use of the del Nido solution was reported most commonly in 38% of respondents, followed by customized solutions in 32%.


Originally, the same cardioplegia formulations used in adults were also used in pediatric patients. However, in the 1990’s, the del Nido cardioplegia solution was created for myocardial protection of the immature myocardium of neonates and pediatric patients. At the present time, it is increasingly being utilized for myocardial preservation during adult cardiac surgery.


Although the current del Nido cardioplegia solution has evolved from the original cardioplegia formulations, it is unique in that it contains lidocaine. It contains a base solution of Plasma-Lyte A, with an electrolyte composition resembling extracellular fluid. A one-liter formulation of del Nido cardioplegia includes the following: Plasmalyte-A (1L), magnesium (2 g, 4 mL), potassium chloride (26 mEq, 13 mL), mannitol (3.26 g, 16 mL), sodium bicarbonate (13 mEq, 13 mL) and lidocaine (130 mg, 13 mL). Calcium is not added, although a small amount of calcium is derived from the addition of whole blood. This formulation is deemed to arrest the heart in diastole. The del Nido solution is generally used as a single-dose of 20 mL/kg. Larger doses may be needed for patients with a thickened myocardium, aortic insufficiency or other conditions where myocardial protection is more challenging. Compared to other formulations, del Nido cardioplegia has been reported to provide comparable myocardial protection, longer cardiac arrest time from a single dose, and lower total volumes of cardioplegia solution with less hemodilution.


It is important for cardiac anesthesiologist to be familiar with cardioplegia solution types used during cardiac surgeries. Multiple dosing with high total volume for complex surgeries leads to hemodilution. Although the accumulation of cardioplegia components such as potassium and lidocaine are usually not clinically significant, awareness and perspective on this information is relevant.


REFERENCES


Sinha P. Myocardial Protection. In: Jonas RA, ed. Comprehensive Surgical Management of Congenital Heart Disease. 2nd Edition. Boca Raton, Florida: CRC Press, Taylor and Francis Group, LLC; 2014: 214-216.


Waterford SD, Ad N. Del Nido cardioplegia: Questions and (some) answers. J Thorac Cardiovasc Surg. 2021;S0022-5223(21)01676-7.


Matte GS, del Nido PJ. History and use of del Nido cardioplegia solution at Boston Children's Hospital [published correction appears in J Extra Corpor Technol. 2013 Dec;45(4):262]. J Extra Corpor Technol. 2012;44(3):98-103.


Ginther RM Jr, Gorney R, Forbess JM. Use of del Nido cardioplegia solution and a low-prime recirculating cardioplegia circuit in pediatrics. J Extra Corpor Technol. 2013;45(1):46-50.


Kotani Y, Tweddell J, Gruber P, et al. Current cardioplegia practice in pediatric cardiac surgery: a North American multi-institutional survey. Ann Thorac Surg. 2013;96(3):923-929.


Haranal M, Chin HC, Sivalingam S, et al. Safety and Effectiveness of Del Nido Cardioplegia in Comparison to Blood-Based St. Thomas Cardioplegia in Congenital Heart Surgeries: A Prospective Randomized Controlled Study. World J Pediatr Congenit Heart Surg. 2020;11(6):720-726.