Final answer:
Retrograde cardioplegia is given through the coronary sinus during CPB with MIDCAB to induce cardiac arrest and protect the heart muscle by allowing an even distribution of cardioplegic solution, particularly when arterial delivery is not feasible.
Step-by-step explanation:
Retrograde cardioplegia involves the administration of cardioplegic solution into the heart in a direction opposite to normal blood flow, typically during cardiac surgery to induce cardiac arrest and protect the heart muscle from damage. In the context of CPB (Cardiopulmonary Bypass) with MIDCAB (Minimally Invasive Direct Coronary Artery Bypass), retrograde cardioplegia is often administered through the coronary sinus, which allows for the solution to distribute evenly in the heart, especially when arterial delivery may be compromised or not possible due to the MIDCAB approach.
The process usually involves cannulation of the coronary sinus, either directly or via a balloon catheter, followed by delivering the cardioplegia at a controlled pressure and temperature. This practice helps to ensure that the myocardium (heart muscle) receives a bloodless field and is protected during the period of ischemia when the coronary arteries are being bypassed.