Myocardial protection with cold blood potassium cardioplegia during prolonged aortic cross-clamping

[Intermittent warm blood cardioplegia--an experimental study]

The influence of intermittent warm blood cardioplegia (WBCP) on myocardial function and metabolism was studied. Fourty-two adult mongrel dogs were used. The isolated heart of one dog was perfused by the cross circulation method with another support dog. The dogs then were divided into three groups. In group I (n = 6), the empty beating heart was perfused with warm blood (WB) kept at 36 degrees C for 100 minutes. In group II (n = 7), the arrested heart was perfused with continuous WBCP using modified Fremes solution for 100 minutes. In group III (n = 8), the arrested heart was perfused with WBCP for 10 minutes following a 15-minute non-perfusion period. This perfusion method was repeated four times. The E max, LV developed pressure, +/- LV dp/dt and LVEDP were all measured to evaluated the myocardial function. In addition, the coronary venous blood pH, myocardial oxygen consumption, myocardial lactate extraction, coronary blood flow, myocardial high energy phosphate content and myocardial water content were also studied in order to elucidate the myocardial metabolism. Regarding the myocardial function, no significant difference was observed between the three groups. The results of chemical studies on the myocardial metabolism were as follows: (1) the coronary venous blood pH in group III decreased at the end of the no perfusion period of WBCP. But it thereafter gradually returned to the normal physiological range; (2) the myocardial oxygen consumption in group III increased just after each interruption, but then gradually decreased toward following intermittent WBCP; (3) the myocardial lactate extraction decreased at the end of the non-perfusion period. However, it gradually returned to the control value by the end of each period of WBCP perfusion; (4) after 60 minutes of reperfusion, the coronary venous blood pH, myocardial oxygen consumption and myocardial lactate extraction showed no significant differences between the groups; (5) the coronary blood flow in group III increased significantly after 1 minute of reperfusion; (6) the ATP value in group III decreased significantly after 60 minutes of reperfusion. The ADP and AMP values demonstrated no significant difference between the groups during the same period; and (7) no significant difference was seen in the myocardial water content between the groups after 60 minutes of reperfusion. It is thus concluded that 10 minutes of intermittent WBCP followed by a 15-minute interruption appeared to have no deleterious effect on the myocardial function and metabolism.

Resuscitative retrograde blood cardioplegia. Are amino acids or continuous warm techniques necessary?

This experiment was designed to determine the relative degree of cardiac functional recovery provided by various forms of resuscitative retrograde blood cardioplegia after global ischemic injury. Twenty-four dogs were subjected to 20 minutes of normothermic global myocardial ischemia followed by 60 minutes of cardioplegic arrest by one of three methods: group 1, standard cold blood cardioplegia with a cold terminal dose (n = 8); group 2, aspartate-glutamate-enhanced blood cardioplegia with warm induction and terminal enhancement (n = 8); and group 3, continuous warm blood cardioplegia (n = 8). Sonomicrometry was used to analyze left ventricular function for maximal elastance and preload recruitable stroke work area. Data were recorded at baseline and after 30 and 60 minutes of unloaded reperfusion. The results showed improved early recovery of preload recruitable stroke work area, but not of maximal elastance, after reperfusion of ischemic hearts with warm resuscitative blood cardioplegic solution enhanced with amino acids. The functional improvement provided by this technique was transient, however, and no significant differences were detectable among the groups after 60 minutes of unloaded reperfusion. Neither amino acid enhancement nor continuous warm cardioplegia offered a significant advantage in functional recovery over the standard method of cold blood cardioplegia reperfusion.

Initial experience with low-potassium cold blood cardioplegia: a clinical comparative study

This study presents the results of bypass grafting in 96 patients operated on for triple-vessel coronary artery disease between May 1988 and September 1990. In the first 54 patients a cold crystalloid solution was employed, and in the 42 more recent patients cold blood low-potassium cardioplegia was employed. There were no differences in postoperative cardiac index or left ventricular stroke work index. Yet, in patients with impaired prebypass left ventricular stroke work index, postbypass left ventricular performance correlated negatively with duration of aortic cross-clamping in the cold crystalloid group (r = -0.441, p = 0.045). In contrast, no correlation was found in the cold blood low-potassium group (r = 0.125, p = 0.587). The incidence of myocardial infarction, need for inotropic support, and need for intraaortic balloon counterpulsation were similar among the groups. Release of the myocardial isoenzyme creatine kinase-MB from 12 to 30 hours after operation was significantly less in the low-potassium blood cardioplegia group. The use of low-potassium blood cardioplegia resulted in a marked reduction in the operative administration of fluids (1,527 +/- 87 versus 3,511 +/- 148 mL; p less than 0.001). In conclusion, low-potassium cold blood cardioplegia is a simple and effective method of myocardial protection. The fact that left ventricular stroke work index recovery was not dependent on the duration of aortic occlusion and that release of the MB isoenzyme of creatine kinase was reduced in the low-potassium blood cardioplegia group implies better myocardial protection.

Effect of cardioplegic preservation on intracellular calcium transients

Intracellular Ca2+ ([Ca2+]i) plays a pivotal role in the regulation of cardiac function. We investigated the effect of cardioplegic preservation on [Ca2+]i transients in the isolated and perfused guinea pig heart loaded with a fluorescent Ca2+ indicator (fura-2). The measurements of [Ca2+]i transients and isovolumetric left ventricular pressure revealed that [Ca2+]i transients and mechanical responses to [Ca2+]i were markedly altered during 15 minutes of normothermic global ischemia and after reperfusion. First, [Ca2+]i transients remained during ischemia without generation of active force of contraction. Such a manifestation of depressed sensitivity of the myofilaments to Ca2+ persisted for the first 5 minutes after reperfusion. Second, the amplitude of [Ca2+]i was diminished during ischemia and reperfusion. Third, diastolic [Ca2+]i was increased during ischemia and especially at the onset of reperfusion. Bolus infusion of cold St. Thomas' Hospital solution abolished [Ca2+]i transients and left ventricular pressure development at an end-diastolic level. Moreover, improved recovery of left ventricular function during reperfusion afforded by the hypothermic cardioplegia was intimately related to its ability to modulate impaired [Ca2+]i transients and mechanical responses to [Ca2+]i; improvement of systolic left ventricular function appears to be produced by restoration of Ca2+ sensitivity of the myofilaments and the amplitude of [Ca2+]i transients, whereas better diastolic compliance of the left ventricle is ascribed to significantly lower diastolic [Ca2+]i. These results may provide new insight into the mechanism of cardioplegic preservation on the basis of [Ca2+]i transients.

Comparison of bretylium and lidocaine in the prevention of ventricular fibrillation after aortic cross-clamp release in coronary artery bypass surgery

The authors compared bretylium and lidocaine for reducing the incidence and persistence of ventricular fibrillation following aortic cross-clamp release performed during coronary artery bypass surgery. Thirty-three adult patients scheduled for elective bypass surgery were randomly assigned in a double-blind fashion to receive a bolus of bretylium, 10 mg/kg, lidocaine, 2 mg/kg, or saline, in equal volumes prior to the release of the aortic cross-clamp. Coronary artery bypass surgery was conducted using standard cardiopulmonary bypass (CPB) procedures with systemic cooling to 24 degrees to 28 degrees C. Temperature, arterial blood gases, and electrolytes were recorded. After clamp release, the first electrical rhythm was noted. Abnormal rhythms (ventricular fibrillation) were allowed to persist for 1 to 2 minutes, and if spontaneous conversion to a supraventricular rhythm did not occur, defibrillation with internal DC countershocks was applied. Patients were compared with respect to occurrence of ventricular fibrillation, need for DC countershocks, antiarrhythmic drugs, and inotropic support. There was no significant difference among the groups with respect to age, sex, preoperative medications, past medical histories, ejection fractions, average number of bypasses, cross-clamp times, or temperatures during bypass. The incidence of ventricular fibrillation after aortic cross-clamp removal was: saline 91%, lidocaine 64% (P less than 0.01), and bretylium 36% (P less than 0.01). The number of countershocks required to defibrillate, while lower in the bretylium group, did not reach statistical significance. After cardiopulmonary bypass, cardiac output and systemic vascular resistance were comparable. Bretylium warrants further study in this setting.

Potassium-induced cardioplegia: evolution and present status

Most cardiac surgical procedures performed in 1989 are accomplished with the aid of some type of controlled, chemically induced cardiac standstill. Although the physiological principles involved were described in the late 19th century, the first clinical application was not until 1955. Because many surgeons believed that myocardial injury resulted from the toxicity of the agents used, the technique was largely abandoned for about 15 years. With the increasing volume of coronary revascularization surgery and with the need for protection of donor hearts intended for orthotopic transplantation, chemically induced cardiac standstill became more appealing and the technique was revived and reevaluated in several centers. In the last several years, the constitution of cardioplegic solutions and the methods by which they are delivered have been greatly modified. Although the most effective solution and technique may yet remain to be described, unquestionably controlled chemically induced cardiac standstill has contributed substantially to the ease and safety with which cardiac surgical procedures can be accomplished. This vignette, although far from complete, outlines some of the important works that have contributed to the evolution of cardioplegic techniques.

Coronary artery bypass grafting for unstable angina pectoris: risk analysis

Unstable angina pectoris is a broad, nonspecific diagnosis encompassing a wide variety of clinical syndromes. The intravenous administration of nitroglycerin preoperatively is indicative of a more acute clinical situation, and allows for selection and analysis of a more homogeneous patient population. We reviewed the results of coronary artery bypass grafting for unstable angina defined as angina necessitating intravenous administration of nitroglycerin preoperatively. There were 129 patients (83 men and 46 women) with a mean age of 63.2 years (range, 36 to 86 years). Complications included operative death in 6.2%, postoperative low cardiac output in 11%, and perioperative myocardial infarction in 9%. Twenty perioperative variables were analyzed to identify risk factors for these end points. For operative death, age (p less than 0.05), cross-clamp time (p less than 0.05), and cardiopulmonary bypass time (p less than 0.001) were significant in the univariate analysis, but only age (p less than 0.05, F = 4.6) was an independent predictor using multivariate analysis (stepwise linear regression). For low cardiac output, univariate analysis demonstrated that cross-clamp time (p less than 0.01), preoperative use of an intraaortic balloon for angina (p less than 0.05), left ventricular score (p less than 0.05), number of diseased coronary vessels (p less than 0.05), and cardiopulmonary bypass time (p less than 0.001) were significant variables. However, only use of an intraaortic balloon for angina (p less than 0.0001, F = 14.3) and left ventricular score (p less than 0.005, F = 11.1) were significant independent predictors in the multivariate model. For perioperative myocardial infarction, only diabetes requiring insulin (p less than 0.005) was a significant predictor.

Comparative use of cold blood potassium cardioplegia in coronary bypass patients necessitating long (2.5-6 h) versus short (less than 1.5 h) aortic cross-clamp times

In symptomatic patients with severe diffuse multivessel coronary disease undergoing bypass surgery, complete revascularization with multiple bypass grafts using saphenous vein and internal mammary conduits, and multiple endarterectomies may be necessary. Such complex surgeries may require long aortic cross-clamp times in excess of 2.5 h. To evaluate the myocardial preservation provided by cold potassium blood cardioplegia, two groups of consecutive patients using nearly similar surgical techniques were compared. Group A consisted of 100 patients who received an average of 3.8 grafts per patient and had a mean aortic cross-clamp time of 66 (range 15-90) min. Group B was comprised of 100 patients who received an average of 9.3 grafts per patient and had a mean cross-clamp time of 187 (range 150-351) min. Operative mortality and perioperative myocardial infarction were low (0-2%) and were not significantly different between the groups. In addition, the postoperative creatine kinase-MB isoenzyme levels, use of pharmacologic and/or mechanical (i.e., intra-aortic balloon) support, and follow-up exercise treadmill tests were not significantly different in the two groups. These findings suggest that cold potassium blood cardioplegia is equally protective of the myocardium during surgical revascularization in patients with short aortic cross-clamp times (less than 1.5 h) as in those with severe diffuse multivessel coronary artery disease requiring long cross-clamp times exceeding 2.5 h and up to 6 h.

Comparison of washed blood and oxygenator whole blood as vehicles for sanguinous multidose cardioplegia

The effects of washed blood or oxygenator-traumatized whole blood as vehicles for sanguinous cardioplegia were studied utilizing the isolated blood-perfused dog heart preparation. Hearts were subjected to 2 hr of potassium-induced arrest at 27 degrees C followed by 90 min of normothermic reperfusion. Washed blood cardioplegia (n = 7) contained blood washed thrice with saline while oxygenator blood cardioplegia (n = 6) contained whole blood which had been exposed to an extracorporeal circuit for 30 to 45 min. Cardioplegic solutions were administered at a perfusion pressure of 100 mm Hg every 15 min during arrest. While the arrest-reperfusion sequence caused minor variations in the mechanical, metabolic, and biochemical parameters tested, generally insignificant differences were found to exist between groups. Differences in coronary washout PCO2 appeared to be due to inherent differences between the two cardioplegic solutions. Thus, while washing blood may be thought to be beneficial and whole blood from the extracorporeal circuit may be theorized to have a deleterious effect on the myocardium, excellent recovery of mechanical function was observed with both cardioplegic solutions. The present study suggests that it is unnecessary to wash the sanguinous cardioplegic solution obtained from the cardiopulmonary circuit.

Comparison of the effectiveness of myocardial preservation in right atrium and left ventricle

Ten patients underwent cardiac operations during which myocardial preservation was provided by systemic hypothermia, topical cardiac cooling, and cold blood cardioplegia. The duration of ischemia ranged from 45 to 142 minutes (mean, 84.2 +/- 36.2 minutes). Two serial specimens (preischemic and ischemic) were obtained from the right atrium and the left ventricle, respectively; thus, a total of 40 biopsy specimens was obtained from these 10 patients. A combination of grading of ischemic injury and stereological morphometric measurement of mitochondria was performed to assess the effectiveness of myocardial preservation. Our findings from the mitochondrial score studies (grading of ischemic injury) were as follows. In the right atrium, the average mitochondrial score rose from 0.337 +/- 0.235 in the preischemic stage to 1.969 +/- 0.492 in the ischemic stage. In contrast, the average mitochondrial score for the left ventricle was only elevated from 0.380 +/- 0.161 to 1.353 +/- 0.396. The difference between preischemia of the right atrium and left ventricle is not statistically significant, but the difference between ischemia of these chambers is significant (p less than 0.01). Our stereological morphometric studies revealed that in the left ventricle, the average mitochondrial surface area was 0.316 +/- 0.046 micron 2 in the preischemic stage and 0.347 +/- 0.073 micron 2 in the ischemic stage, a 9.8% increase in mitochondrial size (not significant). In contrast, the mitochondrial surface area of the right atrium showed a mean increase of 65.8%, from 0.231 +/- 0.038 micron 2 in the preischemic stage to 0.383 +/- 0.057 micron 2 in the ischemic stage (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Concepts and techniques of myocardial protection for adult open heart surgery

Discussions of myocardial protection are often limited to the subject of cardioplegia. However, numerous aspects of operative and perioperative care are of comparable importance. This article outlines the broad topic of myocardial protection, provides strategies for its practical implementation, and reports the author's personal results.

Comparison of blood cardioplegia to electrolyte cardioplegia on the effectiveness of preservation of right atrial myocardium: mitochondrial morphometric study

The right atrium differs from the left ventricle in two respects during cardioplegic arrest: a higher proportion of noncoronary collateral flow is delivered to the right atrium, and the atrium is frequently excluded from topical ice cooling because of its higher position relative to the left ventricle. These factors result in early rewarming of atrial myocardium. To the best of our knowledge, the surgical literature contains no reports on whether blood cardioplegia can provide better atrial myocardial preservation than electrolyte cardioplegia. Twenty consecutive patients who underwent cardiac operations were randomly selected to receive blood cardioplegia (Group 1) or electrolyte cardioplegia (Group 2). Hypothermia was achieved by systemic cooling and continuous topical cooling with ice slush. Stereological morphometric study of mitochondria was performed on 40 biopsy specimens taken from the right atrium prior to aortic cross-clamping (preischemia) and at the end of ischemia. In Group 1, total aortic cross-clamp time was 72.8 +/- 32.5 minutes. The mean mitochondrial surface area before ischemia was 0.224 +/- 0.032 mu 2 and after ischemia, 0.336 +/- 0.032 mu 2, a 50.0% increase in mitochondrial size. In Group 2, total aortic cross-clamp time was 69.7 +/- 30.9 minutes. The mean mitochondrial surface area before ischemia was 0.205 +/- 0.025 mu 2 and after ischemia, 0.439 +/- 0.111 mu 2, an average increase in mitochondrial size of 114.2%. There was no significant difference between the two groups in mitochondrial size before ischemia. However, after ischemia the mean mitochondrial surface areas were significantly different (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of length of aortic occlusion with cold potassium cardioplegia on early and late mortality in cardiac valve replacement

This study determines if prolonged aortic crossclamp time (ACC) with the use of cold potassium cardioplegia during elective cardiac valve replacement contributed to the risk of operative mortality in 225 patients. In Group I (143 patients), the ACC was less than 120 minutes (mean 86) and in Group II (82 patients), it was greater than 120 minutes (mean 146). The preoperative variables showed that Group II contained more severely ill patients who were undergoing more complex operations than in Group I. The operative mortality rate was 7% in Group I and 10% in Group II (p = not significant). Postoperative inotropic support was required in 13% of Group I and 30% of Group II patients (p less than 0.005). Operative mortality in patients in New York Heart Association (NYHA) functional class I and II was 0 and in patients in classes III and IV it was 13% (p less than 0.00008). Five percent of patients in NYHA classes I and II and 32% in classes III and IV required inotropic support (p less than 0.000005). The actuarial survival at 60 months was 88 +/- 3% for Group I and 77 +/- 7% for Group II (NS). For the NYHA class I and II patients, however, it was significantly better (98 +/- 2%) than class III and IV patients (75 +/- 5%) (p less than 0.0001). Analysis by logistic equation revealed that the NYHA functional classes III and IV were significant incremental risk factors for probability of in-hospital mortality (p less than 0.0001) but not the ACC time (p greater than 0.1).(ABSTRACT TRUNCATED AT 250 WORDS)

Myocardial protection during surgical coronary reperfusion

Reperfusion injury in the surgical setting is defined as those metabolic, functional and structural consequences of restoring coronary flow (that is, aortic unclamping and revascularization) that can be avoided or reversed by modification of the conditions of reperfusion by the operating surgeon. The potential for reperfusion damage exists during cardiac surgery because temporary myocardial ischemia (that is, aortic clamping) is needed to produce a quiet, bloodless surgical field. Cold cardioplegic techniques have decreased the risks of ischemic myocardial damage during aortic clamping, but reperfusion damage can still occur when there is poor cardioplegic distribution (that is, coronary artery disease) or in hearts that have suffered ischemic damage before extracorporeal circulation is started (such as extending myocardial infarction, cardiogenic shock and the like). The surgical setting affords the ideal opportunity for reperfusate modification because the components and conditions of the reperfusate are in the surgeon's control. This study reviews present understanding of the nature of reperfusion damage in the surgical setting and summarizes studies over the past 6 years which suggest that much of reperfusion damage can be avoided or reversed by adjusting the temperature, pressure and composition of reperfusate blood.