Cardioplegia is a specialized medical technique used during open-heart surgery to achieve intentional, temporary cardiac arrest (asystole). This procedure allows surgeons to work on a motionless heart, which is necessary for complex repairs like valve replacements or coronary bypass grafting. The arrest is induced by infusing a solution directly into the heart’s circulation. The primary function of this solution is to protect the heart muscle (myocardium) from injury caused by a lack of oxygen supply during surgery. The solution causes cardiac muscle cells to cease electrical and mechanical activity, drastically reducing their metabolic demand.
Classification by Chemical Makeup
The chemical composition of the fluid determines the method of myocardial protection. The two main categories are crystalloid and blood-based solutions. Crystalloid cardioplegia is a clear, electrolyte-rich solution, typically containing a high concentration of potassium chloride to induce diastolic arrest. This simple formulation is straightforward to prepare and administer, offering effective cell protection by paralyzing the cardiac muscle.
A disadvantage of crystalloid solutions is that they dilute the patient’s blood, potentially leading to hemodilution and electrolyte imbalances. Furthermore, crystalloid solutions do not carry oxygen, relying entirely on metabolic suppression during the ischemic period. Conversely, blood-based cardioplegia is a mixture of the arrest solution and the patient’s oxygenated blood, often in a 1:4 ratio. The addition of blood provides oxygen-carrying capacity and natural buffering agents, such as hemoglobin, which better maintain the cellular environment.
The buffering capacity of blood-based solutions helps neutralize acidic metabolic byproducts that accumulate during arrest. Clinicians often regard the addition of oxygen and buffers as providing a more physiologic form of protection. Studies suggest blood cardioplegia can lead to a lower release of post-operative cardiac biomarkers, indicating improved myocardial preservation. Despite these advantages, blood solutions are more complex to administer and may slightly obscure the surgical field compared to clear crystalloid solutions.
Classification by Delivery Route
The method used to deliver the solution into the coronary circulation classifies different cardioplegia approaches, independent of the solution’s chemical makeup or temperature. Antegrade delivery is the traditional method, where the solution flows in the same direction as normal blood flow, into the coronary arteries. Surgeons administer the solution through a cannula placed directly into the aortic root or via catheters inserted into the coronary ostia. This technique is highly effective when the coronary arteries are healthy and unobstructed, ensuring even distribution to the heart muscle.
Antegrade delivery is limited if the patient has severe coronary artery blockages, as the solution cannot reach the downstream tissue. Severe aortic valve insufficiency can also impede this method, causing the solution to backflow into the left ventricle. In these challenging cases, retrograde delivery is often utilized to ensure global protection.
Retrograde delivery involves infusing the solution backward through the cardiac venous system, into the coronary sinus and subsequently into the coronary veins. This method bypasses obstructed coronary arteries and is useful in patients with extensive coronary artery disease. While retrograde infusion provides excellent protection to the deep inner layer of the heart wall (subendocardium), it can result in less uniform distribution to the anterior free wall of the right ventricle. Therefore, many surgeons employ a combined approach, using both antegrade and retrograde sequences to maximize the solution’s reach.
Classification by Temperature Strategy
The temperature at which the cardioplegia solution is delivered dictates the heart’s metabolic response during arrest. Hypothermic (cold) cardioplegia involves delivering the solution at very low temperatures, typically between 4°C and 10°C. The rationale is that cooling drastically slows cellular metabolism, reducing the heart muscle’s oxygen demand by approximately 7% per degree Celsius drop. This suppression allows heart cells to withstand the temporary absence of blood flow for longer periods without damage.
The cold temperature stabilizes cell membranes and slows biochemical reactions that lead to cell injury during ischemia. This strategy is widely used because it effectively extends the safe time available for the surgeon to complete the repair.
Conversely, normothermic (warm) cardioplegia delivers the solution close to normal body temperature, around 37°C. The rationale for using a warm solution is to maintain continuous metabolic activity rather than inducing deep arrest. Warm cardioplegia is often administered as a continuous, slow infusion, providing a steady supply of oxygen and metabolic substrates. This continuous delivery helps wash away acidic byproducts of anaerobic metabolism that accumulate during the ischemic period.
A common variation is the “hot shot,” a final dose of warm, oxygenated cardioplegia delivered just before removing the aortic cross-clamp. This dose is intended to aid in the heart’s metabolic recovery and preparation for reperfusion.
Modern Clinical Variations and Additives
Contemporary cardioplegia practice involves modifications to the core types, often combining strategies for enhanced protection. One variation is the difference between intermittent and continuous delivery. Intermittent dosing involves a large initial dose followed by smaller re-doses every 15 to 20 minutes to maintain arrest and wash out metabolites. Continuous delivery, often used with warm blood cardioplegia, involves a constant, slow infusion throughout the period of cardiac arrest.
Specialized single-dose solutions provide extended protection from one administration. Two prominent examples are Del Nido solution and Custodiol (Histidine-Tryptophan-Ketoglutarate or HTK). Del Nido, originally for pediatric patients, contains additives like lidocaine and magnesium, offering protection for up to 60 minutes. Custodiol is an intracellular-type solution, low in sodium and potassium, using histidine as a buffer for protection lasting up to three hours.
These specialized solutions utilize pharmaceutical additives to enhance cardioprotection beyond simple metabolic arrest. Lidocaine is a sodium channel blocker that stabilizes the cell membrane and reduces electrical activity. Magnesium acts as a calcium antagonist, preventing the harmful influx of calcium ions that can trigger irreversible cell death. The incorporation of these agents allows clinicians to tailor the cardioplegia strategy to the duration and complexity of the surgical case.