Effect of perfusate temperature on myocardial protection from ischemia

Electrolyte versus blood cardioplegia: randomized clinical and myocardial ultrastructural study

In 40 consecutive patients undergoing coronary artery bypass, one of two solutions for cardioplegia, each containing 30 mEq/L of K+ was used randomly. The groups were comparable except for intramyocardial temperature. With electrolyte solution (Group A), it was 16.5 degrees +/- 0.34 degrees C, while with blood from the pump-oxygenator (Group B) it was 20.3 degrees +/- 0.41 degrees C (p less than 0.001). After bypass left atrial pressure (LAP) was 11.9 +/- 0.67 torr in Group A and 8.1 +/- 0.49 torr in Group B (p less than 0.001). CPK-MB was elevated in 45% of Group A patients versus 15% in Group B (p less than 0.05). No patient died. Two myocardial infarctions occurred in Group A and one in Group B. Stereological morphometric electron microscopy was performed on biopsy specimens taken from the left ventricle (1) before perfusion, (2) after cardioplegia, and (3) 30 minutes after reperfusion. Group A showed marked intracellular edema, mitochondrial swelling, pronounced depletion of glycogen stores, and focal myofibrillary disorganization. Group B showed near normal myocardial ultrastructure with increased glycogen stores and minimal mitochondrial swelling. Morphometric analysis revealed a statistically significant increase in the degree of mitochondrial swelling (51%) in Group A compared with Group B after reperfusion (p less than 0.001). Thus, blood K+ cardioplegia resulted in better preservation of myocardial ultrastructure, lower ventricular filling pressure, and lesser CPK-MB release compared with this particular electrolyte cardioplegia.

Improved myocardial preservation at 4 degrees C

We tested the ability of various cardiac preservation techniques to preserve left ventricular function of isolated canine hearts using preservation temperatures of 4 degrees or 15 degrees C. The four techniques tested were: (1) topical hypothermia, and hypothermic arrest induced by (2) perfusion of 1 liter of a modified Collins solution, (3) perfusion of 1 liter of a modified extracellular solution (DKS), or (4) perfusion of 500 ml of blood cardioplegia. Following the cold ischemia period, the hearts were reperfused with blood in the working heart preparation and tested for their ability to recover left ventricular function. Hearts preserved 2 hours at 15 degrees C using hypothermia, modified Collins solution, or DKS solution achieved an average of 60, 73, and 95%, respectively, of baseline function. Hearts preserved 3 hours at 4 degrees C using topical hypothermia attained 70% of baseline function, while hearts stored 5 hours at 4 degrees C using modified Collins solution or DKS solution recovered 83 and 92%, respectively, of baseline function. Hearts preserved at 4 degrees C functioned at levels equal to or greater than that of hearts stored at 15 degrees C, even though the hearts preserved at 4 degrees C were stored for longer periods than those preserved at 15 degrees C. Hearts preserved with blood cardioplegia for 2 hours at either 4 degrees or 15 degrees C achieved functions statistically the same as baseline levels during the reperfusion period. These data show no advantage for preservation temperatures of 15 degrees C compared with 4 degrees C. Our data provide a firm experimental basis for the clinical use of myocardial preservation temperatures of 4 degrees C, especially when combined with cardioplegia.

A thumbtack type of needle thermistor for myocardial protection

The most important and effective factor for myocardial protection during cardiac operation is to keep the myocardium at as low a temperature as possible. The ideal temperature is around 15 degrees C. A thumbtack type of needle thermistor has been developed and used clinically and experimentally during myocardial protection. This type of needle thermistor has several definite advantages.

III. Local cardiac hypothermia: experimental comparison of Shumway's technique and perfusion cooling

A model of the thermal conditions of the heart during ischemic arrest was used to study the efficiency of Shumway's technique of topical hypothermia. Cooling was improved by increasing the flow of cold saline to 350 ml per minute, reducing the saline temperature, lifting the posterior left ventricular wall away from the pericardium, and irrigating the left ventricular cavity. Perfusing the coronary circulation with cold fluid cooled the heart eight times faster than did surface irrigations by Shumway's technique.

Effect of potassium cardioplegia on myocardial ischemia and post arrest ventricular function

To assess the effects of moderate potassium cardioplegia (37 mEq/l KCl) on the severity of myocardial ischemia during arrest and on post arrest ventricular function, 32 isolated, isovolumic feline hearts were studied before, during and 1 hour after ischemic arrest. Normothermia (37 degrees C) was maintained in the remaining 16 hearts, eight without KCl and eight with KCl. Hypothermia (27 degrees C) was maintained in the remaining 16 hearts, eight with KCl and eight without KCl. Myocardial oxygen (PmO2) and carbon dioxide tensions (PmCO2) were measured by mass spectrometry. Maximum developed intraventricular pressure (max DP) and max dP/dt were used as indices of performance. Compared with normothermic or hypothermic arrest alone, the addition of potassium cardioplegia resulted in a significant reduction in the peak PmCO2 measured during the arrest period. Hypothermia alone resulted in morphologic evidence of improved myocardial preservation and a significant reduction in peak PmCO2 compared with normothermia. Post arrest ventricular function was best with the combination of hypothermic arrest and potassium cardioplegia (max DP = 96 +/- 6% of control and max dP/dt = 99 +/- 5% of control). These data suggest that the beneficial effects of postassium cardioplegia and 27 degrees hypothermia are additive, and that reduction in myocardial ischemia as evidenced by a reduction in peak PmCO2 correlated with improvement in ventricular performance in the post arrest period and with preservation of myocardial structure.

A simple method of cold coronary perfusion

Hypothermic coronary perfusion lengthens the safe duration of anoxic arrest. Intermittent selective hypothermic coronary perfusion provides extended myocardial protection. We describe a method of achieving profound myocardial hypothermia by selective deep hypothermic coronary perfusion using a cooling coil without a separate pump head.