Does local cardiac hypothermia during cardiopulmonary bypass protect the myocardium from long-term morphological and functional injury?

Hypothermia with heparin-coated circuits and low dose systemic heparinization in neurosurgery

The purpose of this study was to evaluate the safety of profound hypothermic circulatory arrest with heparin-coated circuits and low dose systemic heparinization in the treatment of cerebral aneurysms. Surgery for giant intracranial aneurysms not operable using standard neurosurgical techniques was performed in 8 patients. All patients were placed on cardiopulmonary bypass using the closed-chest technique, except for the first patient who underwent open-chest bypass. Heparin was administered systemically (3,000 IU) and into the circuit (1,500 IU). Total circulatory arrest was begun at 20 degrees C. The D-dimer, alpha2 plasmin inhibitor-plasmin complex, thrombin-antithrombin III, and beta-thromboglobulin concentrations were measured to evaluate the changes in the coagulation and fibrinolytic systems during bypass. There were no neurologic or cardiac complications. None of the indicators of platelet activation, coagulation, or fibrinolysis were elevated. Hypothermic circulatory arrest combined with heparin-coated circuits and low dose systemic heparinization is safe for use in neurosurgery.

Epicardial damage induced by topical cooling during paediatric cardiac surgery

OBJECTIVE

To study electrocardiographic changes in infants and children in whom topical cooling was used during surgical repair of congenital heart defects.

DESIGN

A retrospective study of all patients who had surgical repair of congenital heart disease during cold blood cardioplegia and topical cooling from January to August 1990. Eleven patients (group 1) had topical cooling with ice and 15 (group 2) with cold saline.

PATIENTS

All 36 paediatric patients operated on during this period. All the available electrocardiographic records were analysed. Ten patients in whom reliable records were not available were excluded. Twenty six patients entered in this retrospective study.

INTERVENTIONS

Topical cooling with ice or with a slush of cold saline.

MAIN OUTCOME MEASURE

Recordings from all the precordial leads were examined and scored as the sum of the maximum ST elevation (mV) in each precordial lead. The score obtained for each electrocardiogram was recorded together with the timing of the electrocardiogram (preoperative, arrival in intensive care unit immediately after surgery, postoperatively in the intensive care unit, and at discharge).

RESULTS

There were no differences between the two groups in terms of demographic data, diagnosis, duration of ischaemia, and postoperative myocardial performance. There was temporary ST elevation during the first 48 postoperative hours in all the children in group 1 but in only seven of the 15 children in group 2 (Fisher's test, p less than 0.005). The mean (SD) score for maximum ST elevation was 1.34 (0.83) mV in group 1 and 0.52 (0.64) mV in group 2 (Student's t test, p less than 0.01).

CONCLUSIONS

These temporary electrocardiographic changes in the presence of adequate myocardial performance were attributed to epicardial damage induced by hypothermicosmotic injury. The use of ice for topical cooling may damage the epicardium in children.

Radionuclide assessment of left ventricular function in patients requiring intraoperative balloon pump assistance

Twenty-three surviving patients who were weaned from cardiopulmonary bypass with intraaortic balloon pump assistance returned for follow-up radionuclide left ventricular (LV) function and thallium 201 perfusion studies at a mean of 23 +/- 3 months following operation. It was found tat despite profound intraoperative myocardial depression requiring intraaortic balloon assistance, 13 patients had no change (within 10%) in the resting LV ejection fraction compared with the preoperative measurement. Among all 23 patients, there was no difference between mean (+/- standard error of the mean) preoperative and postoperative resting LV ejection fraction (48 +/- 4 vs 46 +/- 4%, p = not significant [NS]). Only 11 patients had perioperative myocardial infarction documented by new Q waves in the electrocardiogram, by elevation of creatine kinase-MB fraction, or by defects on thallium 201 imaging not explained by documented myocardial infarction before operation. Overall, postoperative resting LV ejection fraction was not different from the preoperative value in patients with perioperative myocardial infarction (44 +/- 7 vs 47 +/- 5%, p = NS). Postoperative resting LV ejection fraction rose by greater than 10% compared with preoperative values in 4 patients (3 with aortic valve replacement), remained within the 10% limit in 9 patients, and fell by greater than 10% in 10 patients (7 with perioperative myocardial infarction). Only 4 out of 16 patients studied at follow-up with exercise radionuclide studies demonstrated a normal LV response to exercise (greater than 5% increase in LV ejection fraction). Thus, among survivors requiring intraaortic balloon pump assistance for weaning from cardiopulmonary bypass, LV performance at rest is frequently preserved. In addition, 11 of the 23 patients had evidence of perioperative myocardial infarction, indicating a component of reversible intraoperative LV dysfunction.

Myocardial protection from permanent injury during aortic cross-clamping: effectiveness of pharmacological cardiac arrest combined with topical cardiac hypothermia

In two groups of animals (6 and 9 dogs), the aorta was cross-clamped 60 and 90 minutes, respectively, during hypothermic cardiopulmonary bypass. Immediately after cross-clamping, pharmacological cardiac arrest was induced by injecting 100 ml of a cold cardioplegic solution into the aortic root. Topical cardiac hypothermia was added. In hearts undergoing 90 minutes of ischemia, a repeat injection of the cardioplegic solution was done at 45 minutes. In 14 dogs (control group), only topical cardiac hypothermia was instituted for myocardial protection during 60 minutes of ischemia. Seven weeks after operation the surviving animals (6 in each group) were killed. Study of myocardial performance failed to demonstrate significant differences among the groups. Microscopic examination of transmural samples taken from anatomically defined sides of both ventricles, disclosed isolated, punctuate subendocardial scars in only 2 hearts of the control group. All the hearts having 90 minutes of pharmacological cardiac arrest and topical cardiac hypothermia exhibited diffuse fibrosis replacing 10 to 20% of the left ventricular myocardium. Extent and incidence of fibrosis were significantly higher in these hearts in comparison to those of the other groups. We conclude that pharmacological cardiac arrest plus topical cardiac hypothermia makes a safe and efficient method of myocardial protection during aortic cross-clamping only if the ischemic intervals is limited to 60 minutes. It cannot prevent permanent myocardial injury if the ischemic arrest is extended to 90 minutes.