Cardioplegia solutions and delivery methods, and myocardial protection strategies during cardiac surgery.
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- What is the main goal of cardioplegia during cardiac surgery?
- To rapidly arrest the heart in diastole and minimize myocardial oxygen demand, protecting the heart during ischemia
- What ion is elevated in cardioplegia solution to arrest the heart electromechanically?
- Potassium
- What is the mechanism by which high extracellular potassium arrests the heart?
- It depolarizes the resting membrane potential, inactivating fast sodium channels and preventing normal action potential propagation
- What are the two main base fluid categories used for cardioplegia solution?
- Crystalloid cardioplegia and blood cardioplegia
- What is the main theoretical advantage of blood cardioplegia over crystalloid cardioplegia?
- Blood carries oxygen and natural buffering and oncotic properties, providing some ongoing myocardial oxygen delivery during arrest
- What is the typical ratio of blood to crystalloid in standard blood cardioplegia?
- Commonly around 4 parts blood to 1 part crystalloid, though ratios vary by protocol
- What are the two main routes for cardioplegia delivery?
- Antegrade (via the aortic root or directly into coronary ostia) and retrograde (via the coronary sinus)
- What is a key limitation of antegrade cardioplegia delivery in the presence of severe coronary artery disease?
- Distribution may be inadequate distal to critical stenoses or occlusions
- What is a key advantage of retrograde cardioplegia delivery via the coronary sinus?
- It can provide protection to myocardium supplied by severely diseased or occluded coronary arteries independent of native flow
- What is a common combined delivery strategy used to maximize myocardial protection?
- Combining antegrade and retrograde cardioplegia delivery in the same case
- What is the purpose of intermittent cardioplegia redosing during a long cross-clamp period?
- To maintain adequate arrest, replenish protective substrate, and wash out accumulated metabolic byproducts
- What temperature approach is used in cold cardioplegia?
- The solution is delivered cold, often around 4 to 10 degrees Celsius, to further reduce myocardial metabolic rate
- What is warm (normothermic) blood cardioplegia intended to achieve differently than cold cardioplegia?
- Continuous aerobic metabolic support of the arrested heart at near-normal temperature rather than relying primarily on hypothermic metabolic suppression
- What is a 'hot shot' in cardioplegia terminology?
- A terminal warm blood cardioplegia dose given just before releasing the aortic cross-clamp to aid metabolic recovery before reperfusion
- What buffering agent is commonly added to cardioplegia solution to counteract ischemic acidosis?
- Bicarbonate or another buffer such as tromethamine (THAM)
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