Perfusion deficits with retrograde warm blood cardioplegia

Myocardial protection in cardiac surgery: a historical review from the beginning to the current topics

Myocardial protection has become an essential adjunctive measure in cardiac surgery for a couple of decades, because since the 1950s, the methods of cardioprotection (cardioplegic solutions and related procedures) have been improved by the mechanism of myocardial ischemia/reperfusion-induced damage being unveiled through the untiring efforts of researchers and clinicians. The concept of myocardial protection in cardiac surgery was proposed along with introduction of hypothermic crystalloid potassium cardioplegia in the beginning and has been diversified by pharmacological additives, blood cardioplegia, temperature modulation (warm; tepid), retrograde cardioplegia, controlled reperfusion, integrated cardioplegia, and pre-and postconditioning. This historical review summarized experimental and clinical studies dealing with the methods and results of myocardial protection in cardiac surgery, introducing the newly developed concepts for the last decade and the current topics.

Does antegrade blood cardioplegia alone provide adequate myocardial protection in patients with left main stem disease?

BACKGROUND

The optimum route for cardioplegia administration in patients with severe coronary disease is still under debate. This study compared clinical, echocardiographic, and biochemical results in patients with left main stem disease treated with 2 different strategies of myocardial protection.

METHODS

Between March 2000 and November 2002, 148 consecutive patients with left main stem disease undergoing coronary artery bypass grafting were divided into 2 groups according to the route of cardioplegia delivery: antegrade in 87 patients (group A) or antegrade followed by retrograde in 61 patients (group B). Electrocardiography, troponin I, MB-creatine kinase, and MB-creatine kinase mass were performed at 12, 24, 48, and 72 hours postoperatively. Echocardiography was performed preoperatively and before hospital discharge. Data were stratified in subgroups of patients with the following associated risk factors: left ventricular hypertrophy, diabetes, and right coronary stenosis.

RESULTS

Groups were homogeneous in preoperative and intraoperative variables, apart from the higher incidence of unstable angina and severity of left main stem disease in group B. Hospital deaths, intensive therapy unit and hospital stay, perioperative acute myocardial infarction, and intraaortic balloon pump support were similar in both groups. Postoperative recovery of left ventricle ejection fraction and wall motion score index did not differ between the 2 groups. However, postoperative atrial fibrillation was higher in group A (P =.015), especially in patients with diabetes (P <.0001). Troponin I was significantly higher in group A from postoperative hours 12 to 72 (P <.01), and the same pattern was observed in patients with diabetes (P <.001), critical right coronary stenosis (P <.001), and left ventricle hypertrophy (P <.001).

CONCLUSION

The combined route of intermittent blood cardioplegia allows better results in left main stem disease. Such data are confirmed even in risk subgroups.

Efficacy of esmolol as a myocardial protective agent during continuous retrograde blood cardioplegia

OBJECTIVE

Esmolol, an ultra-short-acting beta-blocker, is known to attenuate myocardial ischemia-reperfusion injury. The aim of this study was to compare the effects of esmolol and potassium on myocardial metabolism during continuous normothermic retrograde blood cardioplegia.

METHODS

Forty-one patients operated on for isolated aortic valve stenosis were randomly assigned to continuous coronary infusion with either potassium or esmolol during cardiopulmonary bypass. Myocardial metabolism was assessed by measuring the transmyocardial gradient of oxygen content indexed to left ventricular mass of glucose, lactate, and nitric oxide. To do so, blood samples were simultaneously withdrawn upstream (in the cardioplegia line) and downstream of the myocardium (in the left coronary ostium) 10 and 30 minutes after aortic crossclamping.

RESULTS

Although the cardioplegia flow rate and pressure were similar, esmolol markedly reduced the transmyocardial gradient of oxygen content indexed to left ventricular mass compared with potassium: 13 +/- 6 vs 20 +/- 6 mL of oxygen per liter of blood per 100 g of myocardium, respectively, at 10 minutes and 16 +/- 8 vs 24 +/- 8 mL of oxygen per liter of blood per 100 g of myocardium, respectively, at 30 minutes (P =.009). Coronary glucose and lactate transmyocardial gradients were similar in both groups, indicating adequate myocardial perfusion in all patients at all times. In addition, during retrograde cardioplegia, esmolol showed a lower nitric oxide release compared with that caused by potassium (39 +/- 49 micro mol x L(-1) for potassium vs 14 +/- 8 micro mol x L(-1) for esmolol at 10 minutes and 39 +/- 47 micro mol x L(-1) for potassium vs 6 +/- 8 micro mol x L(-1) for esmolol at 30 minutes, P =.05). However, hemodynamic parameters and plasma troponin I levels remained unchanged postoperatively between the 2 types of cardioplegia.

CONCLUSION

Esmolol provides potent myocardial protection in hypertrophied hearts, at least in part, by reducing myocardial oxygen metabolism.

Retrograde cardioplegia

OBJECTIVE

This study was undertaken to compare the efficacy of retrograde cardioplegia for myocardial perfusion with that of antegrade cardioplegia at the same flow rate.

METHODS

Colored microspheres were used in rat hearts to assess the capillary flow of cardioplegia solution. Myocardial perfusion was evaluated with magnetic resonance imaging in pig hearts. Phosphorus 31 magnetic resonance spectroscopy was used to determine the efficacies of the cardioplegic techniques in sustaining myocardial energy metabolism.

RESULTS

At the same flow rate, the number of colored microspheres delivered to the capillaries by retrograde cardioplegia (15 +/- 1 microspheres/mm2) was significantly lower than that delivered by antegrade cardioplegia (29 +/- 2 microspheres/mm2). Furthermore, only 19% +/- 3% of the colored microspheres delivered to the capillaries by retrograde cardioplegia were found in the arteriolar portions of the capillaries, whereas most (80% +/- 3%) remained in the venular portions. Moreover, magnetic resonance images showed that contrast-enhanced signal-time courses obtained from different regions of the myocardium during retrograde cardioplegia varied significantly. Localized phosphorus 31 spectra showed that retrograde cardioplegia required a higher flow rate than did antegrade cardioplegia to sustain normal myocardial energy metabolism.

CONCLUSIONS

We conclude that retrograde cardioplegia provides significantly less capillary flow than does antegrade cardioplegia. Its microvascular perfusion varies significantly among the various small areas of the myocardium. As a result, its efficacy in sustaining normal myocardial energy metabolism is lower than that of antegrade cardioplegia.

Myocardial perfusion during warm antegrade and retrograde cardioplegia: a contrast echo study

BACKGROUND

We evaluated distribution of warm antegrade and retrograde cardioplegia in patients undergoing coronary artery bypass grafting (CABG).

METHODS

Myocardial perfusion was evaluated pre- and post-CABG using transesophageal echocardiography with injection of sonicated albumin microbubbles (Albunex) during warm antegrade and retrograde cardioplegia. The left ventricle (LV) was evaluated in five segments and the right ventricle (RV) was evaluated in two segments. Segmental contrast enhancement was graded as absent (score = 0), suboptimal or weak (score = 1), optimal or excellent (score = 2), or excessive (score = 3).

RESULTS

Pre-CABG cardioplegic perfusion correlated weakly with severity of coronary artery stenoses (r = -0.331 and 0.276 for antegrade and retrograde cardioplegia, respectively). Antegrade cardioplegia administration resulted in 98% and 96% perfusion to the left ventricle pre- and post-CABG, respectively. Retrograde cardioplegic administration resulted in reduced LV perfusion, with 86% (p = 0.032 from antegrade) and 59% (p<0.001 from antegrade) pre- and post-CABG, respectively. The average LV perfusion score (mean +/- SEM) was greater with antegrade than retrograde cardioplegia both pre-CABG (1.93+/-0.04 vs. 1.53+/-0.11, p<0.001) and post-CABG (1.63+/-0.07 vs. 1.19+/-0.13, p = 0.004). RV perfusion was poor with both techniques pre-CABG, but improved significantly with antegrade cardioplegia post-CABG.

CONCLUSIONS

We conclude that warm antegrade cardioplegia results in better left ventricular perfusion than warm retrograde cardioplegia. Right ventricular cardioplegic perfusion was suboptimal, but the best delivery was achieved with antegrade cardioplegia after coronary bypass. We therefore recommend construction of the saphenous vein graft to the right coronary artery early in the operative procedure.

Does retrograde warm blood cardioplegic perfusion provide better protection of ischemic areas than antegrade warm blood cardioplegic perfusion? A magnetic resonance study in pig hearts

OBJECTIVE

The purpose of this study was to determine whether retrograde continuous normothermic blood cardioplegic perfusion provides better protection to ischemic areas of the left and right ventricles than does antegrade continuous normothermic blood cardioplegic perfusion. Localized phosphorus 31 magnetic resonance spectroscopy was used to monitor the changes in energy metabolism and intracellular pH in the ventricles of pig hearts.

METHODS

Ten isolated pig hearts received 20 minutes of antegrade continuous normothermic blood cardioplegic perfusion for collection of control (baseline) data, followed by 60 minutes of either antegrade continuous normothermic blood cardioplegic perfusion (n = 5) or retrograde continuous normothermic blood cardioplegic perfusion (n = 5) with occlusion of the left anterior descending and the right coronary arteries. The hearts were then subjected to antegrade continuous normothermic blood cardioplegic perfusion for 20 minutes. The perfusion pressures were maintained between 80 and 100 mm Hg and between 38 and 43 mm Hg during antegrade and retrograde continuous normothermic blood cardioplegic perfusions, respectively. Intracellular pH and creatine phosphate, inorganic phosphate, and adenosine triphosphate levels were measured continuously in each ventricle by means of localized phosphorus 31 magnetic resonance spectroscopy with 2 surface coils.

RESULTS

Both antegrade and retrograde continuous normothermic blood cardioplegic perfusion resulted in a significant increase in inorganic phosphate level and decreases in creatine phosphate level, adenosine triphosphate level, and intracellular pH. No significant differences in these changes were observed between the two groups. The creatine phosphate and adenosine triphosphate levels were significantly lower in the right ventricle than in the left ventricle during retrograde continuous normothermic blood cardioplegic perfusion. On reperfusion, the inorganic phosphate level, creatine phosphate level, and intracellular pH recovered completely; however, no recovery in the adenosine triphosphate level was seen in the ventricles of either group.

CONCLUSIONS

Retrograde continuous normothermic blood cardioplegic perfusion does not provide better protection to ischemic areas of the ventricles than does antegrade continuous normothermic blood cardioplegic perfusion under our experimental conditions.

Does simultaneous antegrade/retrograde cardioplegia improve myocardial perfusion in the areas at risk? A magnetic resonance perfusion imaging study in isolated pig hearts

OBJECTIVE

This study was designed to determine whether simultaneous antegrade/retrograde cardioplegia improves myocardial perfusion in areas supplied by occluded vessels.

METHODS

Isolated pig hearts placed in a Langendorff preparation were divided into two groups. The left anterior descending coronary artery was occluded at its origin. In group 1 (n = 7), simultaneous antegrade/retrograde cardioplegia was conducted with use of a single perfusion unit with tubing in a Y-shaped configuration at the end, joined to the aorta and the coronary sinus. In group 2 (n = 8) simultaneous antegrade/retrograde cardioplegia was performed with two separate units, one for antegrade delivery of cardioplegic solution and the other for retrograde cardioplegic solution delivery. Myocardial perfusion in the region supplied by the left anterior descending artery and the region not supplied by this artery was assessed by magnetic resonance imaging, with use of a magnetic resonance contrast agent. The contrast agent was introduced into the common perfusion line in group 1 and into the aortic line only in group 2.

RESULTS

Magnetic resonance images showed that the myocardium in the region supported by the left anterior descending artery could not be perfused with antegrade cardioplegic solution because of occlusion of the artery. During simultaneous antegrade/retrograde cardioplegia, however, the myocardium in the left anterior descending region was perfused by approximately 40% to 50% (group 1) or 20% to 30% (group 2) of the degree of perfusion in the region not perfused by the left anterior descending artery (100%). Almost no cardioplegic solution was delivered to the heart through the coronary sinus route during simultaneous antegrade/retrograde cardioplegia in both groups of hearts. Myocardial perfusion in the region supported by the left anterior descending artery was heterogeneous during simultaneous antegrade/retrograde cardioplegia.

CONCLUSIONS

Simultaneous antegrade/retrograde cardioplegia significantly improved myocardial perfusion in jeopardized areas of the myocardium. The jeopardized myocardium was mainly perfused by the solution drained from the adjacent normal tissue. Elevated pressure at the coronary sinus during simultaneous antegrade/retrograde cardioplegia is responsible for the redistribution of antegradely delivered cardioplegic solution.

Simultaneous antegrade and retrograde delivery of continuous warm blood cardioplegia after global ischemia

OBJECTIVE

Simultaneous delivery of antegrade and retrograde cardioplegia may provide a more homogeneous distribution of cardioplegic solution. It may, however, increase myocardial edema and postcardioplegic myocardial injury. The purpose of this study was to compare simultaneous antegrade-retrograde cardioplegia with antegrade cardioplegia.

METHODS

After 30 minutes of warm, "unprotected," global ischemia, pigs were given warm, continuous blood cardioplegia for 45 minutes (antegrade group, n = 8 and simultaneous antegrade-retrograde group, n = 9). All pigs were weaned from cardiopulmonary bypass 45 to 60 minutes after aortic unclamping. Indices of left ventricular function were measured after another 30 minutes with the conductance catheter technique and pressure-volume loops.

RESULTS

Global left ventricular function, evaluated by preload recruitable stroke work, decreased from baseline values of 126 (102 to 150) (mean [90% confidence limits]) (antegrade) and 122 (116 to 127) erg/ml x 10(3) (simultaneous) to 75 (61 to 89) (p = 0.004) and 95 (79 to 112) erg/ml x 10(3) (p = 0.02), respectively. End-diastolic pressure-volume relation increased from 0.25 (0.21 to 0.28) (antegrade) and 0.30 (0.25 to 0.35) mm Hg/ml (simultaneous) to 0.60 (0.41 to 0.79) (p = 0.009) and 0.53 (0.35 to 0.71) mm Hg/ml (p = 0.02), respectively. The time constant of left ventricular pressure relaxation was unchanged. No intergroup difference was observed in preload recruitable stroke work, preload recruitable stroke work area, end-diastolic pressure volume relation, or stiffness constant. Plasma levels of troponin T increased without any difference between groups. Myocardial water content was increased in the simultaneous group (81.1% [80.7% to 81.5%]) versus the antegrade group (80.1% [79.6% to 80.7%], p = 0.01).

CONCLUSION

Despite a small increase in myocardial water content induced by simultaneous blood cardioplegia, no impairment of postcardioplegic cardiac function was observed compared with antegrade cardioplegia.

Combined antegrade-retrograde blood cardioplegia does not protect right ventricle better than either technique alone in patients with occluded right coronary artery

To study the hypothesis that combined antegrade-retrograde delivery of cardioplegia might overcome the limitations in myocardial protection of either technique alone, we compared the distribution of the different cardioplegic approaches by assessing myocardial cooling and evaluated the effects on right ventricular (RV) function in elective coronary artery bypass grafting (CABG) patients with occluded right coronary artery (RCA). In a randomized trial, 15 patients received exclusively antegrade (ante group), 14 patients received exclusively retrograde (retro group) and 15 patients received combined, alternating antegrade-retrograde (combi group) cold blood cardioplegia. Myocardial temperatures were measured at four sites in the heart. Right ventricular function was assessed by determining the ejection fraction (fast-response thermodilution) and preload-related RV stroke work in repeated measurements. Myocardial cooling was similarly uneven and the posterior wall of the RV remained above 20 degrees C after all three methods of delivering hypothermic (5-7 degrees C) cardioplegia. The RV ejection fraction and preload-related (right atrial pressure) RV stroke work decreased postoperatively similarly in all groups. The results suggest that combined antegrade-retrograde cold blood cardioplegia could not provide more homogeneous myocardial cooling or better RV recovery than either technique alone in three-vessel-diseased CABG patients with occluded RCA.

Ischemic intervals during warm blood cardioplegia in the canine heart evaluated by phosphorus 31-magnetic resonance spectroscopy

OBJECTIVE

Warm blood cardioplegia requires interruption by ischemic intervals to aid visualization. We evaluated the safety of repeated interruption of warm blood cardioplegia by normothermic ischemic periods of varying durations.

METHODS

In three groups of isolated cross-perfused canine hearts, left ventricular function was measured before and for 2 hours of recovery after arrest, which comprised four 15-minute periods of cardioplegia alternating with three ischemic intervals of 15, 20, or 30 minutes (I15, I20, and I30). Metabolism was continuously measured by phosphorus 31-magnetic resonance spectroscopy.

RESULTS

Adenosine triphosphate level fell progressively as ischemia was prolonged; after recovery, adenosine triphosphate was 99% +/- 6%, 90% +/- 1% (p = 0.0004 vs control), and 68% +/- 3% (p = 0.0002) of control levels in I15, I20, and I30, respectively. Intracellular acidosis with ischemia was most marked in I30. After recovery, left ventricular maximal systolic elastance at constant heart rate and coronary perfusion pressure was maintained in I15 but fell to 85% +/- 3% in I20, (p = 0.003) and to 65% +/- 6% (p = 0.003) of control values in I30, while relaxation (tau) was prolonged only in I30 (p = 0.007).

CONCLUSIONS

Hearts recover fully after three 15-minutes periods of ischemia during warm blood cardioplegia, but deterioration, significant with 20-minute periods, is profound when the ischemic periods are lengthened to 30 minutes. This suggests that in the clinical setting warm cardioplegia can be safely interrupted for short intervals, but longer interruptions require caution.

Does retrograde administration of blood cardioplegia improve myocardial protection during first operation for coronary artery bypass grafting?

BACKGROUND

The objective of this study was to evaluate the value of retrograde blood cardioplegia in coronary artery bypass grafting.

METHODS

In 1994 and 1995, 224 patients undergoing first-time isolated coronary artery bypass grafting were randomized to antegrade (112 patients, group 1) or retrograde (112 patients, group 2) administration of blood cardioplegia. In group 1, 76 patients were given warm cardioplegia (at 33 degrees C) and 36 had cold cardioplegia (< 20 degrees C), whereas in group 2 cardioplegia was warm in 77 patients and cold in 35. The two randomization groups had similar demographic and angiographic characteristics. The number of grafted coronary arteries averaged 2.9 +/- 0.7 in group 1 and 2.8 +/- 0.7 in group 2. Total duration of cardiopulmonary bypass (78 +/- 23 and 75 +/- 21 minutes) and of aortic cross-clamping (47 +/- 16 and 46 +/- 16 minutes), total volume of infusion of the crystalloid component of cardioplegia (988 +/- 297 and 1016 +/- 595 mL), and total duration of infusion of cardioplegia (23 +/- 10 and 22 +/- 11 minutes) were similar (p > 0.05).

RESULTS

There was no death in group 1 and one in group 2 as a result of a pulmonary embolus, for a global early mortality of 0.45%. The numbers of perioperative myocardial infarction (5 versus 3), congestive heart failure (4 versus 5), postoperative hemorrhage (4 versus 4), and stroke (1 versus 2) were also similar (p > 0.05). Release curves of total creatine kinase, creatine kinase-MB by serum activity and mass concentration, and troponin T were not significantly different (p > 0.05) between the two groups. For the 216 patients without perioperative myocardial infarction, peak enzyme release of creatine kinase-MB at 24 hours averaged 23 +/- 22 and 20 +/- 18 IU/L, and that of troponin T averaged 1.1 +/- 1.1 and 1.3 +/- 1.5 micrograms/L at 6 hours for the antegrade and the retrograde groups, respectively (p > 0.05).

CONCLUSIONS

Our results indicate no evidence that the retrograde method of cardioplegic infusion improves myocardial protection during first operation for isolated coronary revascularization compared with the usual antegrade route.

Recent Developments in Myocardial Protection: Retrograde Cardioplegia

In recent years there has been increasing use of coronary sinus perfusion to deliver cardioplegic solutions during open-heart surgery. This has been aided by advances in coronary sinus catheter design and by easier methods of cannula insertion. Coronary sinus perfusion has been used with both intermittent crystalloid and blood cardioplegia and has recently evolved to include retrograde continuous normothermic blood cardioplegia. Coronary sinus perfusion has several advantages including safety, ease of use (with a single cannula placed out of the operative field), usefulness in patients with significant aortic regurgitation, redo coronary artery bypass graft surgery, and acute myocardial infarction. However, there are continuing concerns about the distribution of retrograde perfusion, preservation of right ventricular function, dislodgment of the coronary sinus catheter (and resulting ischemia during surgery), and damage to the coronary sinus.

Myocardial protection for cardiac surgery: the nursing perspective

The advancement of myocardial protection techniques is considered to be the most instrumental in achieving successful cardiac surgical outcomes. Although many issues complicate the efficacy of myocardial protection, warm cardioplegia is instituted more often as a better myocardial protection method for patients undergoing cardiac surgery. Understanding differences in patient response between warm and cold cardioplegia is essential for development of appropriate nursing intervention strategies and prevention of postoperative complications. Advanced practice nurses in cardiac surgical settings must continue to evaluate metabolic, functional, and hemodynamic variations of patients with different cardioplegia for positive patient outcomes.

Antegrade and retrograde cardioplegia: alternate or simultaneous?

Neither antegrade nor retrograde cardioplegic protection provides homogeneous distribution, and a combination may be required to avoid anaerobic metabolism and depressed postoperative ventricular function. Tepid cardioplegia (29 degrees C) avoids the delayed recovery of cardiac function and metabolism associated with cold cardioplegia (15 degrees C) and reduces the anaerobic metabolism seen with warm (37 degrees C) cardioplegia. We compared two techniques that combine antegrade and retrograde tepid cardioplegia: alternate and simultaneous.

METHODS

Sixty patients undergoing elective isolated coronary artery bypass grafting were randomized to receive near continuous tepid retrograde and either intermittent antegrade cardioplegia (the alternate technique) or antegrade cardioplegia with the solution delivered concurrently through each completed vein graft (the simultaneous technique).

RESULTS

Myocardial lactate extraction was greater after crossclamp release following simultaneous than alternate cardioplegia. Postoperative ventricular function was better after alternate than simultaneous cardioplegia.

CONCLUSION

Both techniques permitted rapid postoperative recovery of myocardial metabolism and ventricular function. However, simultaneous cardioplegia was simpler and did not require deairing the aortic root between antegrade infusions.

Normothermic techniques during open heart operations

There has been considerable interest in the use of normothermic techniques during cardiac operations, both as a means of myocardial protection and as a more physiologic environment for other organs during cardiopulmonary bypass. Although a limited number of uncontrolled studies have suggested superior clinical results compared with conventional hypothermic regimens, these claims have not been thoroughly investigated using randomized protocols. The limited available data suggest that the successful use of warm blood cardioplegia requires adequate delivery of the solution to all parts of the myocardium at optimal flow rates to maintain aerobic arrest, so those who advocate the use of normothermic arrest must pay particular attention to ensure that their myocardial protection is effective. The advantages of employing normothermic systemic perfusion in regard to factors such as improved hemodynamic performance and reduced blood loss postoperatively need to be balanced against concerns regarding the inadequacy of cerebral protection offered by this method.

Evidence that continuous normothermic blood cardioplegia offers better myocardial protection than intermittent hypothermic cardioplegia

OBJECTIVES

To compare transmyocardial ischaemia and oxidative stress, as well as non-infarction myocardial injury, in patients randomised to intermittent hypothermic cardioplegia or continuous normothermic blood-potassium cardioplegia.

DESIGN

Prospective randomised trial.

SETTING

Tertiary cardiac referral centre.

METHODS

24 patients undergoing elective coronary artery bypass surgery were randomised to hypothermic (13 patients, mean (SEM) age 59.5 (2.6) years) or normothermic (11 patients, mean (SEM) age 59.7 (3.3) years) cardioplegia. Transmyocardial oxidative stress and ischaemia were assessed by the difference in plasma concentrations of oxidised glutathione and lactate respectively, from samples taken simultaneously from the coronary sinus and aortic root. Blood samples were taken just before cross clamp application and at intervals up to 15 min after cross clamp release. Non-infarction myocardial injury was assessed by measurement of creatine kinase MB isoenzyme activity from peripheral venous blood taken 2 and 18 h after surgery.

RESULTS

Intermittent hypothermic cardioplegia resulted in a significant increase in transmyocardial ischaemia (P < 0.001) and oxidative stress (P < 0.001). Evidence of significantly increased myocyte damage was also present (P < 0.01). No significant corresponding changes were present with normothermic cardioplegia.

CONCLUSIONS

Normothermic blood cardioplegia seems to avoid significant changes in myocardial ischaemic status and consequent oxidative stress. This study provides direct evidence that normothermic cardioplegia offers enhanced myocardial protection compared with that of hypothermic cardioplegia. Certain subsets of patients may derive more benefit from normothermic cardioplegia, although it is unclear whether this would be the case for all patients.

Early changes in regional and global left ventricular function after aortic valve replacement. Comparison of crystalloid, cold blood, and warm blood cardioplegias

BACKGROUND

The clinical effects of different cardioplegic methods on left ventricular (LV) function have not been fully elucidated, particularly in the setting of myocardial hypertrophy.

METHODS AND RESULTS

Sixty-four patients (mean age, 62 +/- 12 years; 41 men, 23 women) who were undergoing elective aortic valve replacement (stenosis, 49; regurgitation, 15; concomitant coronary artery bypass grafting, 22), with LV mass index 230 +/- 70 g/m2, were randomized to the following groups: antegrade crystalloid cardioplegia (CCP, 21 patients), antegrade/retrograde cold blood cardioplegia (CBP, 23 patients), or continuous retrograde warm (37 degrees C) blood cardioplegia (WBP, 20 patients). Mean aortic cross-clamp and cardiopulmonary bypass times were 100 +/- 20 and 126 +/- 24 minutes. Positive inotropic drug therapy was required postoperatively in 9 patients after CBP, 14 after CCP, and 18 after WBP. Perioperative LV function was assessed using transesophageal M-mode echocardiography, combined with high-fidelity LV pressure recording and thermodilution cardiac output, before bypass and 0.5, 1, 3, 6, 12, and 20 hours after cross-clamp removal. There was a similar fall in LV peak circumferential wall stress at constant LV end-diastolic dimension in each group after aortic valve replacement. The increase in contraction velocity was significant from 0.5 hour with CBP; however, no significant increase occurred until 12 hours with CCP and until 20 hours with WBP. The rate and extent of LV pressure fall and early diastolic filling rate both increased with CBP, and only in this group did ventricular coordination improve. LV stroke work index was maintained with CBP throughout the postoperative period with less inotropic support than with the other two methods.

CONCLUSIONS

In the hypertrophied LV, CBP offers the best preservation of myocardial physiological response and ventricular function with less inotropic support.

Intermittent warm blood cardioplegia. Warm Heart Investigators

BACKGROUND

Warm heart surgery implies continuous perfusion with normothermic blood cardioplegia. Interruption of cardioplegia, however, facilitates construction of distal coronary anastomoses and is the method practiced by many surgeons. To determine whether intermittency is harmful, we present results from 720 coronary bypass patients, protected with intermittent antegrade warm blood cardioplegia, that were derived from a previous study of normothermic versus hypothermic cardioplegia.

METHODS AND RESULTS

Mean +/- SD age was 60.8 +/- 9.0 years; 27% of cases were urgent; 16% of patients had > 50% left main stenosis, and 19% had grade III or IV ventricles. A mean of 3.2 +/- 0.9 grafts was constructed. The average aortic cross-clamp time was 61.8 +/- 22.2 minutes. The longest single time off cardioplegia (LTOC) averaged 11.4 +/- 4.0 minutes per patient. The cumulative time off cardioplegia as a percentage of the cross-clamp time (PTOC) was 48.2 +/- 18.6% per patient. LTOC and PTOC were divided into quartiles (LTOC, < 10, 10 to 11, 12 to 13, and > 13 minutes; PTOC, < 36%, 36% to 49%, 50% to 62%, and > 62%) and related to the prespecified composite outcome of mortality, myocardial infarction according to serial CK-MB sampling, and low-output syndrome (LOS). Longer LTOC was harmful (event rates per quartile, 13.5%, 10.3%, 10.9%, and 19.0%; P = .046), whereas longer PTOC was protective (16.1%, 17.2%, 9.4%, and 10.6%; P = .07). Stepwise logistic regression was performed, controlling for demographic and angiographic predictors. In the multivariate models, LTOC remained detrimental (P = .07) and PTOC remained beneficial (P = .053). Additional modeling after entering surgeon identity (P < .001) into the risk equation eliminated the PTOC effect, whereas LTOC remained predictive of adverse outcomes (P = .053; odds ratio, 1.06; 95% CI, 1.00, 1.13).

CONCLUSIONS

The data indicate that a reasonable margin of safety exists with intermittent, antegrade warm blood cardioplegia. Repeated interruptions of warm blood cardioplegia are unlikely to lead to adverse clinical results if single interruptions are < or = 13 minutes.

Adequate distribution of warm cardioplegic solution

Seventy-five patients undergoing coronary artery bypass grafting were randomized to receive warm antegrade (N = 25), warm retrograde (N = 25), or a combination of warm antegrade and retrograde (N = 25) delivery of blood cardioplegic solution. Myocardial oxygen utilization, lactate and acid metabolism, and adenine nucleotides and their degradation products were measured during the operation and cardiac function was assessed postoperatively. Warm retrograde delivery of cardioplegic solution increased lactate and acid release during cardioplegia and reperfusion, decreased left ventricular adenosine triphosphate concentrations, and reduced the washout of adenine nucleotide degradation products from both left and right ventricles. Warm antegrade delivery of cardioplegic solution resulted in less lactate and acid release during cardioplegia but more lactate accumulated in the territory of the left anterior descending artery during the crossclamp period. Intermittent antegrade delivery of the cardioplegic solution during combination cardioplegia washed out lactate and acid, which suggested inhomogeneous delivery of the cardioplegic solution during continuous retrograde cardioplegia. Combination cardioplegia best preserved adenosine triphosphate in the left ventricle and resulted in the best postoperative left and right ventricular function. A combination of intermittent antegrade and continuous retrograde delivery of cardioplegic solution provided better myocardial protection than either antegrade or retrograde delivery of cardioplegic solution alone.

Coronary sinus ostial occlusion during retrograde delivery of cardioplegic solution significantly improves cardioplegic distribution and efficacy

This study documents the gross flow characteristics and capillary distribution of cardioplegic solution delivered retrogradely with the coronary sinus open versus closed.

METHODS

Five explanted human hearts from transplant recipients were used as experimental models. Hearts served as their own controls and received two doses of warm blood cardioplegic solution, each containing colored microspheres. The first dose was delivered through a retroperfusion catheter with the coronary sinus open and the second dose was delivered with the sinus occluded. Capillary flow was measured at twelve ventricular sites and gross flow was measured by examining coronary sinus regurgitation, thebesian vein drainage, and aortic effluent (nutrient flow).

RESULTS

Coronary sinus ostial occlusion allowed for a significant decrease in total cardioplegic flow (1.74 +/- 0.40 ml/gm versus 1.06 +/- 0.32 ml/gm; p < 0.05) to occur while maintaining an identical intracoronary sinus pressure. Ostial occlusion also resulted in an increase in the ratio of nutrient flow/total cardioplegic flow from 32.3% +/- 15.1% to 61.3% +/- 7.9% (p < 0.05). A statistically significant improvement in capillary flow was found at the midventricular level in the posterior intraventricular septum and posterolateral right ventricular free wall. This improvement was also documented for the intraventricular septum and right ventricle at the level of the apex.

CONCLUSION

Coronary sinus occlusion during retrograde cardioplegia significantly improves cardioplegic delivery to the right ventricle and posterior intraventricular septum. Furthermore, the technique affords a significant improvement in nutrient cardioplegic flow while reducing the overall volume of cardioplegic solution administered.

Tepid antegrade and retrograde cardioplegia

To determine the optimal temperature for the combination of antegrade and retrograde cardioplegia, 42 patients undergoing coronary artery bypass grafting were randomized to receive cold (9 degrees C; n = 14), tepid (29 degrees C; n = 14), or warm (37 degrees C; n = 14) blood cardioplegia delivered continuously retrograde and intermittently antegrade. Myocardial oxygen utilization, lactate and acid metabolism, and coronary vascular resistance were measured during the operation and cardiac function was assessed postoperatively. Myocardial oxygen consumption, lactate release and acid release were greatest with warm, intermediate with tepid, and least with cold cardioplegia (p = 0.0001). However, washout of lactate and acid at the time of cross-clamp release was reduced (p = 0.022) with tepid or cold compared with warm cardioplegia. Early postoperative left ventricular function was best preserved (p = 0.01) after tepid than after cold or warm combination cardioplegia. These results suggest that tepid combination cardioplegia reduced metabolic demands but permitted immediate recovery of cardiac function. This technique may provide better myocardial protection than cold or warm combination cardioplegia.