An improved method of topical cardiac hypothermia

Pretransplant rinse of hearts preserved with colloid-free UW solution and more effective heart preservation: studies in a rat abdominal heart transplant model

BACKGROUND

University of Wisconsin solution (UW) provides effective heart preservation under hypothermic conditions, but it can be deleterious at warmer temperatures. Re-warming during the implantation of the graft may be a problem. This study examined the damaging effect of peri-operative warm ischemia in a transplant setting and recovery from such damage. The amelioration of damage by rinsing the graft before re-warming and transplantation was also examined.

METHODS

Rat donor hearts were preserved for 2 hr (0 degrees C) as follows: Series A was preserved with colloid-free UW (MUW), St. Thomas' solution (ST), or calcium-supplemented MUW (MUW+Ca) followed by either transplantation or warming (22 degrees C) for 10 min before transplantation. Series B was preserved with MUW, rinsed with fresh MUW, ST, MUW+Ca, or low-potassium MUW before warming and transplantation. All heart isografts were transplanted heterotopically with an indwelling left intraventricular balloon-tipped catheter. Graft function was measured 1 and 7 days after transplantation.

RESULTS

Grafts re-warmed rapidly during implantation. Function (left ventricular developed pressure, contractility, and relaxation) was significantly and persistently diminished in MUW-preserved grafts subjected to additional warming before transplantation. Preservation with ST was less effective than MUW despite being unaffected by warming. Preservation with MUW+Ca and rinsing with fresh MUW or ST before re-warming allowed recovery of function within 7 days despite significantly diminished function on day 1.

CONCLUSION

This study demonstrated that an increase in the peri-transplant warm ischemic period was detrimental when hearts were preserved with MUW. Preservation with calcium-supplemented MUW or rinsing the heart with fresh MUW or ST before transplantation ameliorated this damage.

Cox/maze procedure for atrial septal defect with atrial fibrillation: management strategies

Atrial fibrillation is found at late follow-up in approximately half of all adults who have had correction of atrial septal defect, even if it was not present preoperatively. These patients are thus exposed to the risks of stroke and chronic drug therapy even after a successful operation. Simultaneous surgical correction of atrial septal defect and atrial fibrillation was accomplished in a 52-year-old man by means of the Cox/maze procedure. The small added risk and the substantial benefit of eliminating atrial fibrillation suggest that this approach is warranted in selected adults with atrial septal defect.

Technical considerations for coronary artery bypass without cardioplegia

Coronary artery bypass without cardioplegia remains the preferred technique at many centers around the world. This report describes in detail a technique that emphasizes intermittent cross-clamping of the aorta at mild hypothermia (30 degrees C). Since coronary bypass procedures require brief interruptions of coronary blood flow only for the distal anastomoses, the duration of myocardial ischemia with this technique is not prolonged by unexpected changes in the operative plan. Many bypass grafts can also be carried out without cross-clamping of the aorta by using local control of the coronary arteries. The increasing number of elderly patients with atherosclerotic aortas that cannot be safely clamped makes it helpful for all cardiac surgeons to be familiar with noncardioplegic techniques.

Phrenic Nerve Injury Following Cardiac Surgery, with Emphasis on the Role of Topical Hypothermia

Phrenic nerve dysfunction that develops after cardiac surgery has generally been attributed to the topical hypothermia used for myocardial preservation and protection. Although studies relying on postoperative radiographic findings to establish the diagnosis reveal an incidence as high as 73%, investigations employing electrophysiological assessment indicate a 10% incidence. Most patients who sustain phrenic injury during cardiac surgery do not suffer major respiratory morbidity; those who do generally recover. In addition to the role of topical hypothermia as a major etiological factor, physical trauma or compromise of the vascular supply to the phrenic nerve and diaphragm may also be important factors. Although a number of measures have been advocated to lower the incidence of the problem, none have been evaluated in a prospective, randomized study using electrophysiological techniques. This review focuses on the incidence, underlying mechanisms, and clinical and electrophysiological recognition of phrenic nerve dysfunction following cardiac surgery.

Continuous versus intermittent cardioplegia in the presence of a coronary occlusion

Coronary artery occlusions can alter the distribution of cardioplegia and result in ischemic damage. This study was undertaken to determine whether continuous antegrade cardioplegia delivery would result in colder temperatures and provide better washout of acid metabolites than is possible with intermittent antegrade cardioplegia when coronary occlusions are present. Twenty pigs were placed on cardiopulmonary bypass and underwent 2 hours of ischemic arrest with occlusion of the middle left anterior descending coronary artery followed by 1 hour of reperfusion without occlusion of that artery. Ten pigs received intermittent (every 20 minutes) antegrade potassium crystalloid cardioplegia (4 degrees C), and 10 others had the same solution given continuously (30 mL/min). Cardioplegia distribution was assessed by continuous monitoring of myocardial pH (Khuri pH probe) and temperature in the region beyond the occlusion of the left anterior descending coronary artery. Both cardioplegic techniques resulted in tissue acidosis (continuous group, 6.69 +/- 0.08, versus intermittent group, 6.73 +/- 0.07; not significant). Average temperature in the left anterior descending coronary artery during arrest was also similar in both groups (continuous group, 18.3 degrees +/- 0.5 degrees C, versus intermittent group, 18.2 degrees +/- 0.5 degrees C). Because of these metabolic changes, both cardioplegic techniques resulted in abnormal wall motion in the anteroseptal region using two-dimensional echocardiography, but the scores were not significantly different (continuous group, 1.5 +/- 0.3, versus intermittent group, 1.6 +/- 0.4; 4 = normal to 0 = dyskinesia).(ABSTRACT TRUNCATED AT 250 WORDS)

Phrenic nerve injury. A prospective study

In cardiac surgery, topical iced saline solution slush has become an important adjunct in maintaining myocardial hypothermia during cardioplegic arrest. One complication of this technique is phrenic nerve injury (PNI). In an attempt to reduce the incidence of PNI, a prospective study was undertaken to evaluate the impact of phrenic nerve insulation on PNI during cardiac surgery. Seventy-six consecutive patients who underwent coronary revascularization constituted the control group (CG) and were compared with 76 patients who underwent a similar procedure with the addition of phrenic nerve insulation. In the intervention group (IG), a foam insulation pad was placed between the heart and the pericardium in an effort to reduce exposure of the phrenic nerve to iced saline solution slush. There was no difference in major demographic descriptors or operative variables between the CG and the IG, except that the internal mammary artery was used more frequently in the IG (64 percent vs 36 percent, p = 0.0006). The in-hospital mortality was similar between the groups (CG, 0.0 percent; IG, 1.3 percent; p = 1.0); however, the incidence of roentgenographically diagnosed PNI was much greater in the CG (14/76 patients [18 percent] vs 0/76 patients [0 percent]; p = 0.0006). Patients with and without PNI were similar with regard to age, gender, aortic cross clamp time, cardiopulmonary bypass time, and number of grafts (p greater than 0.05). All unilateral PNI occurred on the left. Three patients with bilateral PNI required tracheostomy and prolonged mechanical ventilation. In-hospital mortality was similar for patients with and without PNI (0 percent vs 0.7 percent), but mean postoperative hospital stay for patients with clinically diagnosed PNI was longer than for those without PNI (32 vs 11 days, p = 0.04). This prospective study demonstrates that the incidence of PNI can be significantly reduced by the routine use of phrenic nerve insulation.

Optimizing myocardial hypothermia: II. Cooling jacket modifications and clinical results

After induction of myocardial hypothermia by cold cardioplegic solution, myocardial rewarming occurs at 0.5 degrees to 1.0 degrees C/min. In addition to preventing myocardial rewarming from systemic and pulmonary venous return, continuous cooling of the myocardial surface must be provided. Modifications of a previously reported cooling jacket are described. These modifications include decreased width and thickness of the metal skeleton for easier application and increased malleability, respectively. Also, the double-row flow channel markedly minimizes obstruction of flow secondary to kinking and allows inlet and outlet lines to attach at adjacent points of the jacket thus minimizing obstruction of the operative field. The effectiveness of the jacket in 36 patients undergoing valve replacement and 19 patients having pulmonary thromboendarterectomy was evaluated by measurement of myocardial temperatures at multiple sites throughout aortic cross-clamping. Temperatures at all sites were maintained at 12 degrees C or less. Temperatures measured in phrenic nerve pedicles ranged from 25 degrees to 27 degrees C. During cooling, heat removal by the jacket was 330 calories/min. During maintenance of myocardial hypothermia, heat flow was 190 calories/min. Modifications of a cooling jacket facilitate usability and an array of sizes enhances applicability.

Myocardial preservation

The principles used to develop techniques for myocardial preservation in cardiac surgery have been successfully applied to the protection of the donor heart in transplant surgery. This article reviews the latest advances in myocardial preservation during cardiac surgery and shows how they have been adopted in current cardiac transplant techniques.

Recent advances in cardiopulmonary bypass and the clinical application of myocardial protection

Basic scientific research has provided the impetus to develop cardioplegic solutions that offer excellent myocardial preservation. Future research will continue to develop methods for better delivery of cardioplegia to all myocardial regions. In addition, earlier detection of evolving ischemic damage during aortic cross-clamping might provide a basis for earlier intervention to reverse developing myocardial injury. At the present time, the cardiac surgeon has many cardioplegic solutions and delivery systems from which to choose. Only by understanding the principles involved in myocardial preservation will the surgeon be able to develop a system that will work best in his or her clinical practice.

Patient care problems in patients undergoing reoperation for coronary artery grafting surgery

Over the past six years there has been a 15-fold increase in the number of patients requiring reoperation coronary artery bypass grafting (RCABG) surgery at the University of Alabama in Birmingham. To determine the perioperative risk, a retrospective chart survey of one calendar year's (1981) experience was made comparing the 58 RCABG patients with 59 cohorts undergoing primary operation. All patients were anaesthetized with diazepam, fentanyl and halothane or enflurane anaesthesia. Preoperative evaluation revealed by history that the incidence of unstable angina and digoxin use were greater (p = 0.05) in the RCABG patients. Cardiac catheterization revealed a higher incidence (26 vs 89 percent) of left main coronary disease in controls and similar indices of left ventricular function (wall abnormalities, ejection fraction and LVEDP). Operating and bypass times were longer (p less than 0.01) for RCABG patients and there was a trend for greater (p = 0.08) use of dopamine in the RCABG patients. CK-MB release was significantly (p less than 0.05) greater in RCABG patients. Serious postoperative complications (CK-MB greater than or equal to 15 IU/L, low cardiac output, and death) were significantly (p = 0.02) greater in the RCABG group. It is concluded that RCABG patients represent a greater risk of complications and that new strategies for improving myocardial protection need to be developed to reduce the risk.