Cardioplegia

Question 1

List the purposes of cardioplegia solution use in cardiac surgery

Answer 1

Myocardial Protection:

Cooling of the Heart
Cardiac Arrest in Diastole and manipulation of the extracellular environment to minimise ongoing metabolic activity and its deleterious consequences during a period of suboptimal perfusion

Facilitation of surgery

Still relaxed heart
Bloodless Field

Question 2

Give the typical composition of cardioplegia solution and how this composition has its physiological effect on the myocardium

Answer 2

High Potassium Concentration (approx 20mmol/L)

This has the physiological effect of arresting the heart in diastole- the high extracellular potassium concentrations prevent repolarisation of the myocytes through causing inactivation of the fast inward voltage-sensitive sodium channels that are important in phase 0 of the action potential

Calcium at a lower concentration than plasma

Calcium is required to maintain cell membrane integrity, however, it is also required for muscle contraction, Hence the physiological effect of keeping the calcium low is to prevent/avoid myocardial activity

Magnesium Concentration exceeding the normal plasma level

The physiological effect here is that it prevents Magnesium loss from cells, which allows it to maintain its role as an enzymatic cofactor. Magnesium also competes with Calcium and hence reduces calcium-induced contraction.

Sodium and Chloride are usually at levels near those found in plasma

(Alternatively low sodium concentration can be used as the mechanism to induce cardiac arrest)

Bicarbonate, histidine or other buffer

To offset the tendency to metabolic acidosis associated with ischaemia

Mannitol

To raise the osmolarity of the solution, thus reducing tissue oedema

Procaine

Reduction of arrhythmias at reperfusion

Blood

For increased oxygen carrying capacity

Question 3

By which routes can cardioplegia be administered

Answer 3

Anterograde:

Specialised cannulae are placed into the ascending aorta or directly into the coronary ostia.

This route is dependent on: adequate root pressure, good coronary perfusion and a competent aortic valve

Retrograde:

This is administered through a canula inserted into the coronary sinus

Question 4

What are the possible complications of cardioplegia solution administration

Answer 4

** Remember that issues that may arise from the method of administration count as well as those from the cardioplegia itself**

Direct vessel damage associated with canulation

Dislodgement of plaque on cannulation, resulting in embolic stroke or myocardial infarction

Air bubbles in cardioplegia solution causing air emboli in the coronary arteries or systemic circulation, with consequent ischaemia

Failure to attain widespread cardiac perfusion with the cardioplegia leaving areas of myocardium warm and active whilst ischaemic

Fluid Overload

Haemodilutiion

Anaemia

Myocardial oedema, haemorrhage, and or injury as a result of high infusing pressures

Post-operative electrolyte derangement with consequent risk of arrhythmia

Postoperative acid-base disturbance and dilution of clotting factors with a negative impact on coagulation