Inadequate cardioplegic protection with obstructed coronary arteries

Determinants of Inadequate Cardioprotection in Adult Patients with Left Ventricular Dysfunction

BACKGROUND

 Perioperative cardioprotection is essential for achieving satisfactory clinical outcomes in heart failure patients. It is important to understand the factors affecting perioperative cardioprotection.

METHODS

 The institutional database was searched for patients with reduced ejection fraction (EF, < 40%) who underwent surgery with cardioplegia-induced arrest. Patients were divided into del Nido cardioplegia (DN) and cold blood cardioplegia (CB) groups. The relationships between age, preoperative blood parameters, creatinine, cross-clamp time (CCT), extracorporeal circulation time (ECT), and postoperative troponin values at 12 hours or deterioration of EF (≥5%) were evaluated. Baseline characteristics, operative parameters, and outcomes were analyzed.

RESULTS

 There were 508 patients with reduced EF (331 DN and 177 CB). In the entire cohort, anemic patients had greater troponin values (p = 0.004) as well as in the DN group (p = 0.002). However, this was not detected in the CB group (flat regression line; p = 0.674). Patients with high leukocyte values had greater troponin release (entire cohort: p < 0.001; DN group: p < 0.001; CB group: steep regression line with p = 0.042). Longer CCT and ECT were associated with greater troponin release (entire cohort; both groups) and greater risk of fall in EF. In a direct comparison, fewer patients had significant deterioration of EF in the DN group than CB group (3.9 vs. 11.9%; p < 0.001).

CONCLUSION

 The use of CB cardioplegia may be beneficial in anemic patients, whereas the use of DN cardioplegia may be beneficial for expected long CCT and high leukocytosis.

Comparison of simultaneous antegrade/vein graft cardioplegia with antegrade cardioplegia for myocardial protection

Antegrade cardioplegic delivery via the aorta ensures distribution of cardioplegic solution through open arteries, but distribution may not be adequate beyond a stenotic coronary artery. This potential problem can be overcome by direct delivery of cardioplegia via a vein graft. The purpose of this study was to compare simultaneous antegrade/vein graft cardioplegia with antegrade cardioplegia during coronary artery bypass surgery. Twenty patients were divided into 2 groups. In group 1, intermittent antegrade cardioplegia was provided (n=10). In group 2, intermittent antegrade cardioplegia was supplemented by antegrade perfusion of vein grafts after distal anastomoses were completed (n=10). Data on enzyme release and hemodynamics were obtained preoperatively, before the induction of anesthesia, just before cross-clamping, immediately after aortic unclamping, and at 1, 6, 12, 24, and 48 h after unclamping. Enzyme release (creatinine phosphokinase-isoenzyme MB, cardiac troponin I, myoglobin) was similar in both groups (P>.05). Furthermore, no significant difference was noted in the incidence of postoperative low cardiac output syndrome, perioperative myocardial infarction, or ventricular arrhythmia (P>.05). In conclusion, both techniques permitted rapid postoperative recovery of myocardial function. Supplementation of antegrade perfusion of vein grafts with antegrade cold blood cardioplegia offered no advantage to study patients.However, hemostasis of a distal anastomosis may be controlled by this technique.

Retrograde crystalloid cardioplegia preserves left ventricular systolic function better than antegrade cardioplegia in patients with occluded coronary arteries

OBJECTIVE

To investigate retrograde and antegrade crystalloid cardioplegia in terms of cardiac cooling and postoperative cardiac function.

DESIGN

Prospective, randomized, and blinded.

SETTING

University hospital.

PARTICIPANTS

Twenty male patients with triple-vessel disease and proximal occlusion of the circumflex or the left anterior descending coronary artery.

INTERVENTIONS

Left ventricular ejection fraction at rest and during exercise was evaluated by nuclear ventriculography the day before and 3 months after surgery. After induction of anesthesia and hourly for the first 5 postoperative hours, hemodynamic, echocardiographic, and electrocardiographic data were acquired. Myocardial temperature was measured with needle thermistors in 3 myocardial regions.

MEASUREMENTS AND MAIN RESULTS

Demographic and temperature data were analyzed by t-test. Hemodynamic and echocardiographic data were analyzed by analysis of variance. The groups were similar in baseline characteristics. Retrograde cardioplegia cooled the region distal to an occlusion better than antegrade cardioplegia (9.6 degrees C +/- 4.8 degrees C v 21.8 degrees C +/- 5.9 degrees C; p < 0.01). Hemodynamic, echocardiographic, and electrocardiographic data did not differ between the groups. Three months after surgery, the retrograde cardioplegia group showed a higher left ventricular ejection fraction at rest (58% +/- 10% v 47% +/- 10%; p < 0.02) and during exercise (58% +/- 13% v 47% +/- 10%; p < 0.05) compared with the antegrade cardioplegia group.

CONCLUSIONS

Retrograde cardioplegia provides more homogenous myocardial cooling than antegrade cardioplegia in hearts with coronary artery occlusions. The use of retrograde cardioplegia seems to benefit long-term left ventricular function.

Warm or cold continuous blood cardioplegia provides similar myocardial protection

BACKGROUND

This study was performed to investigate the effect of temperature of blood cardioplegia on the recovery of postischemic cardiac function.

METHODS

Pigs on cardiopulmonary bypass were subjected to global ischemia (30 minutes), followed by cold (n = 10) or warm (n = 11) continuous antegrade blood cardioplegia (45 minutes) delivered at 55-60 mm Hg.

RESULTS

Global left ventricular function, evaluated by preload recruitable stroke work, decreased with cold cardioplegia from 91 (85-103) [mean (quartile interval)], at baseline, to 73 (55-87) erg x 10(3)/mL postbypass (p = 0.03), but was unchanged after warm cardioplegia; 110 (80-132) to 109 (71-175) erg x 10(3)/mL (p > 0.5). However, the difference between treatment effects was not significant (p = 0.25). Diastolic function, evaluated by end-diastolic pressure-volume relation, deteriorated without any difference between groups. Mean cardioplegic flow was similar between groups. Coronary vascular resistance increased at constant rate during warm cardioplegic delivery, but remained unchanged with cold cardioplegia (p = 0.001 between regression coefficients).

CONCLUSIONS

No significant difference was found in postischemic functional recovery comparing cold and warm continuous blood cardioplegia. Cold cardioplegia is therefore preferred due to added safety of hypothermia.

Antegrade-Retrograde Cardioplegia for Myocardial Protection during Coronary Artery Bypass Graft Surgery

This prospective randomized clinical study was designed to assess and compare the use of combined antegrade-retrograde cardioplegia versus antegrade cardioplegia in providing adequate myocardial preservation during coronary artery bypass graft surgery. Fifty patients undergoing elective coronary artery bypass grafting were randomly divided into 2 groups according to the route of cardioplegic delivery: group A (25 patients) received antegrade cold crystalloid cardioplegia; group B (25 patients) received combined antegrade-retrograde cold crystalloid cardioplegia. The groups were compared by clinical and electrocardiographic criteria and biochemical markers of ischemic myocardial damage. There was a highly significant statistical difference between the groups in terms of spontaneous recovery of sinus rhythm (40% of patients in group A versus 96% in group B). The use of direct current shock to restore sinus rhythm was higher in group A (60%) compared with group B (4%). Low cardiac output occurred in 20% of patients in group A and in 16% of patients in group B but this difference was not statistically significant. No bundle-branch block was found in group B whereas the incidence was 8% in group A. Significantly higher levels of biochemical markers of myocardial damage were obtained in group A at 10 minutes, 4 hours, and 12 hours after declamping. These results indicate that combined antegrade-retrograde cardioplegia is superior to antegrade cardioplegia for myocardial protection during coronary artery bypass graft surgery.

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.

Single aortic cross-clamp technique in coronary surgery: a prospective randomized study

OBJECTIVE

To test the hypothesis of an improved myocardial and cerebral protection by combining blood cardioplegia and the single aortic cross-clamp technique, 100 patients were enrolled in a prospectively randomized study and stratified for preoperative conditions.

METHODS

In Group I, 55 patients underwent myocardial revascularization using crystalloid cardioplegia and the conventional partial occluding clamp technique to perform proximal anastomoses, whereas in Group II, 45 patients were operated on combining blood cardioplegia and the single aortic cross-clamp technique. Unstable angina, emergency procedures, reoperations and preoperative counterpulsation accounted for an higher risk score in group II patients (P < 0.03). Operations were performed by the same surgical team. Aortic cross-clamp time was significantly longer in group II patients (59 +/- 22 vs. 47 +/- 18 min.) (P < 0.001). Other intraoperative variables were not significant.

RESULTS

A 70-year-old male in group I died on post-operative day 5 as a consequence of a major neurological event. Length of ventilatory dependency, post-operative bleeding, need for blood transfusions, ICU stay, and hospital stay were similar between the two groups (P = NS). Patients in group I showed a strict correlation between the duration of surgical ischemia and post-operative myocardial necrosis. Analysis of combined mortality and morbidity events (adverse events) between the two groups, led to a significant prevalence in group I patients (P < 0.03) in spite of an higher pre-operative risk score and longer ischemic times in group II patients. Neurological lesions remained confined to group I patients.

CONCLUSIONS

The combined use of blood cardioplegia, delivered via the antegrade and retrograde routes, and the single-clamp technique to perform myocardial revascularization, might enhance myocardial and cerebral protection when compared to conventional methods. Larger groups of patients are needed to support this trend.

Assessment of retrograde cardioplegia with magnetic resonance imaging and localized 31P spectroscopy in isolated pig hearts

OBJECTIVE

This study was done to determine whether retrograde delivery of cardioplegic solution provides uniform blood flow to the myocardium supplied by an occluded coronary artery and whether it maintains myocardial energy levels beyond the coronary occlusion.

METHODS

Isolated pig hearts were used. A hydraulic occluder was placed at the origin of the left anterior descending coronary artery. The perfusion pressure for retrograde delivery of cardioplegic solution was controlled at 40 to 50 mm Hg. Magnetic resonance imaging and localized 31P magnetic resonance spectroscopy were used to assess myocardial perfusion and energy metabolism, respectively.

RESULTS

Magnetic resonance perfusion images (n = 7) showed that the perfusion defect that occurred during antegrade delivery of cardioplegic solution (as a result of the occlusion of the left anterior descending coronary artery) resolved during retrograde delivery of cardioplegic solution. Retrograde perfusion delivered similar amounts of flow to the jeopardized myocardium as it did to other areas of the myocardium. However, the distribution of cardioplegic solution by the retrograde route was heterogeneous (cloudlike) across both ventricular walls. 31P magnetic resonance spectra showed that the ischemic changes induced by occlusion of the left anterior descending artery during antegrade perfusion were greatly alleviated by retrograde perfusion; however, it took longer for retrograde cardioplegia (n = 7, 17.08 minutes) to restore the levels of inorganic phosphate/phosphocreatine relative to the effect of releasing the left anterior descending artery occluder during antegrade delivery of cardioplegic solution (n = 7, 5.3 minutes).

CONCLUSIONS

First, retrograde delivery of cardioplegic solution provides sufficient flow to the myocardium beyond a coronary occlusion to maintain near normal levels of energy metabolites, and second, the efficacy of the retrograde route of cardioplegic solution delivery (in terms of distribution of the solution and rate of myocardial energy recovery) is significantly lower than that of the antegrade route.

Effect of cardioplegia infusion pressure on coronary artery endothelium and cardiac mechanical function

OBJECTIVE

Monitoring of cardioplegia infusion pressure may be important, particularly in immature hearts and in hearts without coronary artery disease. We have investigated the effects of infusion pressure on the preservation of the isolated rat heart.

METHODS

Hearts (five in each group) were subjected to a single (20 ml) infusion of St. Thomas' Hospital cardioplegic solution at pressures of 60, 120, 180 and 240 cmH2O (44-176 mmHg), followed by 30 min of hypothermic (20 degrees C) ischemia.

RESULTS

Mean recovery of cardiac output (expressed as a percentage of its preischemic value) decreased with increasing infusion pressure: 96.1 +/- 0.6%, 87.3 +/- 2.1% (P < 0.05 vs. 60 cmH2O), 79.3 +/- 2.8% (P < 0.05 vs. 120 cmH2O), 72.0 +/- 3.0% (not significant vs. 180 cmH2O), respectively. Endothelial function, as assessed by pre- and post-ischemic ability to secrete NO in response to 5-hydroxytryptamine, remained relatively normal after infusion at 60 cmH2O, but changed from vasodilation to vasoconstriction after infusion at 240 cmH2O. Electron microscopy revealed mild endothelial damage after infusion at 240 cmH2O, which was greatly exacerbated by reperfusion and was accompanied by regions of myocyte damage compatible with reperfusion of unprotected myocardium. The relationship between cardioplegia infusion pressure and infusion time was not linear and implied that infusion pressures greater than 120 cmH2O caused vascular smooth muscle constriction.

CONCLUSIONS

These results suggest that even mildly raised cardioplegia infusion pressures may be detrimental to cardiac preservation and the effects are possibly mediated through endothelial damage and pressure-induced coronary vasoconstriction.

Myocardial cooling and right ventricular function in patients with right coronary artery disease: antegrade vs. retrograde cardioplegia

BACKGROUND

Protection of the right ventricular (RV) myocardium during ischaemia in cardiac surgery is difficult, especially in patients with severe right coronary artery (RCA) disease. Retrograde coronary sinus cardioplegia is thought to distribute uniformly, but doubts still remain as to its adequacy in RV preservation. This study evaluated distribution of antegrade vs. exclusively retrograde coronary sinus cold blood cardioplegia by assessing myocardial cooling and compared the effects on RV function.

METHODS

Fifty-eight patients scheduled for elective coronary artery surgery-29 patients with significant RCA disease and another 29 with no significant RCA stenosis (controls)-were randomised to receive either antegrade or retrograde cold blood cardioplegia through either aortic root or conventional self-inflating coronary sinus catheter (RCA-ante, RCA-retro, C-ante and C-retro groups). RV function was assessed by fast-response thermodilution. Myocardial temperatures were measured in the anterior and posterior wall of the right and left ventricle.

RESULTS

Cooling of the posterior wall of the RV was effective only in the control patients given antegrade cardioplegia (14.7 degrees C), whereas in the other groups the lowest myocardial temperatures there remained above 20 degrees C (P < 0.001). In patients with obstructed RCA both antegrade and retrograde cold cardioplegia led to uneven cooling of the myocardium. After cardiopulmonary bypass the RV ejection fraction (RVEF), RV stroke work index (RVSWI) and cardiac index (CI) were significantly reduced in the RCA-retro group, and RVSWI and CI in the C-retro group, too. Regression analysis showed an inverse relationship between the temperatures of the posterior walls of the ventricles and changes in the RVEF and CI.

CONCLUSIONS

Retrograde and antegrade cardioplegia alone were not effective in reducing the temperature of the posterior wall of the RV in the patients with obstructed RCA, in whom with retrograde cardioplegia RV haemodynamics were impaired for 1 hour following bypass. Neither retrograde nor antegrade cardioplegia alone can be relied on to protect the posterior wall of the RV in the patients with obstructed RCA.

Evaluation of Ventricular dP/dt Before and After Open Heart Surgery Using Transesophageal Echocardiography

The mean dP/dt during isovolumetric contraction (mean dP/dt(ic)) is a new echocardiographic index of ventricular function that has been shown to approximate and closely correlate with invasively measured peak dP/dt. It is amenable to rapid measurement via transesophageal echocardiography (TEE) and is theoretically independent of variations in ventricular anatomy and wall motion. It is therefore well suited for the assessment of ventricular function during surgery. The purpose of this study was to assess the clinical value of TEE determinations of mean dP/dt(ic) before and after cardiopulmonary bypass (CPB). The mean dP/dt(ic) of 50 patients undergoing open heart surgery for a variety of congenital and acquired heart defects was measured before and 15-30 minutes after CPB. Mean dP/dt(ic) averaged 1147 +/- 492 before and 1428 +/- 702 mmHg/sec after CPB (P < 0.01). Mean dP/dt(ic) was unchanged or increased in 45 patients and fell in only 5 patients. It increased significantly even among patients who did not receive supplemental inotropic agents. Mean dP/dt(ic) correlated well with the shortening fraction, especially among patients without segmental left ventricular wall-motion abnormalities. The general patterns observed for mean dP/dt(ic) were also seen when the data was corrected for variations in heart rate. A preoperative mean dP/dt(ic) < 765 mmHg/sec or a heart rate corrected mean dP/dt(ic) < 620 mmHg/sec indicated a high likelihood that inotropic support would be needed to facilitate weaning from CPB. Mean dP/dt(ic) may be a clinically useful, quantitative TEE index of perioperative changes in ventricular contractility.

The regional effect of retrograde cardioplegia in areas of evolving ischemia

Retrograde cardioplegia (RCP) is often used for myocardial protection during coronary bypass grafting, but the regional effect of RCP in areas of evolving ischemia is unknown. We examined the functional and metabolic indices of regional myocardial preservation following acute coronary occlusion with evolving ischemia in a canine model. Following the institution of 37 degrees C cardiopulmonary bypass in 14 dogs, the left anterior descending artery (LAD) was occluded for 15 min. The hearts were then subjected to 90 min of cardioplegic arrest (12 degrees C, 15 mL/kg every 30 min). Seven had antegrade cardioplegia (ACP) alone, while seven had ACP until arrest, then RCP. No topical cooling was used. The LAD occlusion was released after the first bolus of cardioplegia. Regional temperature and pH were measured in the LAD and circumflex (nonischemic) distributions. After 90 min of ischemia and 30 min of reperfusion, all dogs were weaned from bypass. Postischemic function was determined globally by the return of developed pressure (%dP/dt) and regionally by ultrasonic wall crystals. End-ischemic ATP preservation in the LAD distribution was assessed by HPLC (mm ATP/mg protein). Results show that regional functional and metabolic indices were better maintained with RCP in the ischemic LAD distribution. Although only moderate reduction of global function was seen with ACP, the severe reduction noted in LAD regional wall motion with ACP reflects poor regional protection that can be significantly improved in evolving ischemia with RCP.

Resistance of the failing dystrophic hamster heart to the cardioprotective effects of diltiazem and clentiazem: evidence of coronary vascular dysfunctions

Although hypothermia and cardioplegic cardiac arrest provide effective protection during cardiac surgery, ischemia of long duration, poor preoperative myocardial function, and ventricular hypertrophy may lead to heterogeneous delivery of cardioplegic solutions, incomplete protection, and impaired postischemic recovery. Calcium antagonists are potent cardioprotective agents, but their efficacy in the presence of cold cardioplegia is still controversial, especially in heart failure, since it is often believed that failing hearts are more sensitive to their negative inotropic and chronotropic actions. However, recent data have demonstrated that the benzothiazepine-like calcium antagonists diltiazem and clentiazem, in selected dose ranges, elicit significant cardioprotection independently of intrinsic cardiodepression, thus lending support to their use in cardioprotective maneuvers involving the failing heart. We therefore evaluated the cardioprotective interaction of diltiazem, clentiazem, and cold cardioplegia in both normal and failing ischemic hearts. Hearts were excised from 200- to 225-day-old cardiomyopathic hamsters (CMHs) of the UM-X7.1 line and age-matched normal healthy controls. Ex vivo perfusion was performed at a constant pressure (140 cmH2O; 1 cmH2O = 98.1 Pa) according to the method of Langendorff. Heart rate, left ventricular developed pressure (LVDP), and coronary flow were monitored throughout the study. Global ischemia was produced for 90 min by shutting down the perfusate flow, followed by reperfusion for 30 min. Normal and failing CMH hearts were either untreated (control) or perfused at the onset of global ischemia with one of the following combinations: cold cardioplegia alone (St. Thomas' Hospital cardioplegic solution, 4 degrees C, infused for 2 min), cold cardioplegia + 10 nM diltiazem, or cold cardioplegia + 10 nM clentiazem. The cardiac and coronary dilator properties of 10 nM diltiazem and 10 nM clentiazem alone were investigated in separate groups of isolated preparations. Failing CMH hearts had lower basal LVDP (42 +/- 2 vs. 77 +/- 2 mmHg (1 mmHg = 133.3 Pa) for normal hearts, p < 0.05), while coronary flow was only slightly reduced (5.6 +/- 0.2 vs. 6.2 +/- 0.2 mL/min for normal hearts). Following 90 min global ischemia, coronary flow was increased in both groups, but the peak hyperemic response declined only in failing CMH hearts (+50 +/- 17 vs. +82 +/- 17% in normal hearts). In normal hearts, LVDP virtually recovered within 5 min of reperfusion but steadily decreased thereafter (-37 +/- 4% at 30 min). In contrast, in failing CMH hearts, LVDP significantly decreased early during reperfusion but improved over time (-19 +/- 7% at 30 min). In normal hearts, the addition of diltiazem or clentiazem to cold cardioplegic solutions resulted in improved postischemic contractile function for the duration of reperfusion (85 +/- 4% vs. only 71 +/- 6% for cardioplegia, p < 0.05). The post-ischemic increase in coronary flow was similar in all groups. In failing CMH hearts, the addition of diltiazem or clentiazem afforded no significant contractile benefit at reperfusion. In nonischemic normal hearts, infusion of diltiazem or clentiazem (10 nM) alone increased coronary flow (+6 +/- 1% for diltiazem and +24 +/- 3% for clentiazem) without significant negative inotropic or chronotropic effects. In nonischemic failing CMH hearts, infusion of diltiazem or clentiazem did not elicit cardiodepression. In contrast their coronary dilator actions reverted to vasoconstriction (diltiazem) or were significantly attenuated (clentiazem). From these experiments we can conclude that, compared with the normal heart, the failing CMH heart adapted differently to global ischemia.

Retrograde cardioplegia does not adequately perfuse the right ventricle

Surgeons often rely primarily on retrograde cardioplegia for myocardial protection, because it provides adequate left ventricular perfusion even in the presence of coronary artery disease. Clinically, however, adequate right ventricular perfusion by retrograde delivery has not been demonstrated. Using intraoperative transesophageal echocardiography, we examined retrograde delivery of cardioplegic solutions by contrast echocardiography, which directly assesses myocardial perfusion. In 15 patients (seven having coronary bypass and eight having valve operations), 4 ml of sonicated Isovue medium was injected retrograde via a coronary sinus catheter. Myocardial perfusion was assessed quantitatively by visual inspection and back-ground-subtracted videodensitometric analysis. In five patients undergoing aortic valve replacement, right and left coronary ostial drainage was estimated during retrograde infusion. Before the aortic crossclamp was removed, myocardial oxygen extraction was calculated in all 15 patients by first delivering warm blood cardioplegic solution for 2 minutes in a retrograde fashion and then taking samples from the cardioplegia line and aortic root. This determined the oxygen extraction ratio across the myocardium at the end of retrograde delivery. Warm blood cardioplegic solution was next given antegrade, and 15 seconds later samples were taken from the cardioplegia line and a right ventricular (acute marginal) vein to determine the oxygen extraction ratio across the right ventricle. As assessed by contrast echocardiography, retrograde infusion resulted in almost four times more perfusion to the left ventricular free wall and septum than to the right ventricular free wall (74 +/- 2 versus 69 +/- 2 versus 20 +/- 2, p < 0.05). In those five patients with an aortotomy the right ostial drainage was less than 5 ml/min whereas left ostial drainage was estimated at 80 ml/min during retrograde administration. Oxygen extraction across the myocardium supplied by retrograde infusion was low after 2 minutes. Conversely, when antegrade cardioplegia was started, right ventricular oxygen extraction rose fourfold (42% +/- 5% versus 11% +/- 1%, p < 0.05), demonstrating that retrograde cardioplegia had not adequately perfused the right ventricular myocardium.

CONCLUSIONS

1. Retrograde cardioplegia provides poor right ventricular myocardial perfusion as assessed by contrast echocardiography and coronary ostial drainage. (2) This poor perfusion is inadequate to meet myocardial demands as demonstrated by the high right ventricular oxygen extraction after a prolonged retrograde infusion. (3) Therefore surgeons must not rely solely on retrograde cardioplegia for right ventricular myocardial protection. This concept is especially important if continuous warm blood cardioplegia is used, because myocardial requirements are then higher.

Risk factors of incomplete distribution of cardioplegic solution during coronary artery grafting

Myocardial distribution of cardioplegic solution infused by combined antegrade/retrograde routes was assessed with myocardial contrast echocardiography in 18 patients with chronic stable angina and three-vessel disease undergoing elective coronary artery bypass grafting. Overall myocardial opacification was significantly greater in retrograde than in antegrade cardioplegia (77.7% +/- 13.4% versus 59.1% +/- 15.7%; p = 0.0009). The difference was affected by collateral circulation, as pointed out by the significant interaction between coronary collateral circulation and percent of myocardial opacification after antegrade and retrograde cardioplegia (p = 0.002). When we performed multiple comparisons, in patients with good collaterals the opacification difference between antegrade and retrograde cardioplegia was not statistically significant (66.4% +/- 10.2% versus 76.0% +/- 15.2%; p = not significant), whereas in patients with poor collaterals myocardial opacification during retrograde cardioplegia was significantly greater (44.3% +/- 15.0% versus 81.2% +/- 9.0%; p < 0.02). During antegrade cardioplegia, patients with poor collaterals showed a lower degree of myocardial opacification than patients with good collaterals (44.3% +/- 15.0% versus 66.4% +/- 10.2%; p < 0.01). Our results show that retrograde cardioplegia in patients undergoing elective coronary artery bypass grafting offers no advantage over antegrade cardioplegia when collateral circulation is well developed. On the other hand, conventional aortic root infusion may not provide adequate myocardial protection in the subset of patients with significantly narrowed or occluded coronary arteries and poor collaterals.

Intermittent ischaemic arrest and cardioplegia in coronary artery surgery: coming full circle?

OBJECTIVE

To compare the cardioprotective efficacy of cold crystalloid cardioplegia and intermittent ischaemic arrest in patients undergoing elective coronary artery surgery.

DESIGN

Prospective randomised trial.

SETTING

London teaching hospital.

SUBJECTS

20 patients with at least moderately good left ventricular function undergoing elective coronary artery surgery by one experienced surgeon and needing at least two bypass grafts.

INTERVENTIONS

Patients were randomised to cold crystalloid cardioplegia or intermittent ischaemic arrest.

MAIN OUTCOME MEASURES

The primary determinant of the efficacy of myocardial protection was serial measurement (before and at 1, 6, 24, and 72 hours after the end of cardiopulmonary bypass) of cardiac troponin T (cTnT), a highly sensitive and specific marker of myocardial damage.

RESULTS

There was no significant difference in age, ejection fraction, number of grafts, bypass times, or cross clamp times between the two groups. One patient in the cardioplegia group had a perioperative infarct and was excluded from further study. In both groups there was a significant increase in cTnT, with peak concentrations being reached 6 hours after the end of cardiopulmonary bypass and remaining significantly high at 72 hours. At 6 hours the median (75% interquartile range) concentrations of cTnT were similar in both groups (1.8 (1.0-3.6) micrograms/l for cardioplegia v 1.9 (1.0-3.5) micrograms/l for intermittent ischaemic arrest).

CONCLUSION

This trial shows that intermittent ischaemic arrest, even without systemic cooling or venting of the left ventricle, provides a similar level of myocardial protection to cardioplegia in patients with moderate left ventricular function and short ischaemic times.

Single-clamp technique: an important adjunct to myocardial and cerebral protection in coronary operations

To determine the myocardial and cerebral protective properties of the single cross-clamp (group I; n = 160) versus the partial occluding clamp (group II; n = 150) technique for construction of the proximal anastomoses, a retrospective analysis of 310 patients operated on by the same surgeon was performed. Group I patients were older (median age, 70 versus 64 years; p < or = 0.0001), with 83 (52%), versus 41 (27%) in group II, 70 years and older (p < or = 0.0001). More group I patients were in New York Heart Association functional class IV (42 [26%] versus 22 [15%]; p = 0.008); more required preoperative balloon counterpulsation (35 [22%] versus 16 [11%]; p = 0.006); and more required emergent operation (20 [13%] versus 3 [2%]; p < or = 0.0001). Antegrade crystalloid cardioplegia was used in both groups. The median cross-clamp time was 58 minutes for group I versus 44 minutes for group II (p < or = 0.0001). However, there was no significant difference between the two groups in terms of the number of bypass grafts, the use of the mammary artery, or the bypass time. The operative mortality was 2.5% (n = 4) for group I versus 5.3% (n = 8) for group II (p = 0.16), and the perioperative myocardial infarction/low cardiac output state was seen in 6 patients (3.8%) in group I versus 18 patients (12%) in group II (p = 0.006). The median creatine kinase MB release was 13 U/L for group I versus 19 U/L for group II (p = 0.0029).(ABSTRACT TRUNCATED AT 250 WORDS)

Improved myocardial protection by antegrade perfusion in combination with coronary sinus occlusion in the presence of left anterior descending artery obstruction

The present study was undertaken to evaluate the improved protection of antegrade aortic root perfusion combined with intermittent coronary sinus occlusion (APCSO) for the 1-hour ischemic myocardium in the presence of left anterior descending artery occlusion, 12 dogs were divided into 2 groups: anteperfusion (AP) alone (n = 6) and APCSO (n = 6). The experimental results showed that APCSO provided a better cardioplegic distribution and a lower hypothermia (15.6 degrees C versus 17.2 degrees C) in the occluded LAD region, compared with AP. After ischemia, cardiac index and left ventricular stroke index recovered excellently in APCSO (128% to 141% and 115% to 158% of preischemic values, respectively), and much worse in AP (69% to 82% and 53% to 73% of preischemic values, respectively). Our study has confirmed that APCSO is superior to AP in myocardial protection in the presence of coronary artery occlusion.

Myocardial protection by retrograde cardioplegic perfusion in the presence of acute coronary artery obstruction. An experimental study

To investigate retrograde delivery of cardioplegic solutions as a means of enhancing myocardial protection in the presence of coronary artery occlusion, a two-part experimental model was devised. In part 1 (in vitro) the possibility of retroperfusing the entire myocardium during acute occlusion of the left anterior descending artery (LAD) was assessed. In part 2 (in vivo) acute LAD occlusion was performed in dogs, and during 2 hours of aortic cross-clamping crystalline cardioplegic solution was infused at 20-minute intervals. In group I the infusion was antegrade, via the aortic root, and in group II it was retrograde, via the coronary sinus. Thereafter the LAD snare was released and the dogs were weaned from bypass. Delivery of cardioplegia through the aortic root was associated with depression of ventricular function, poor myocardial cooling and severe cellular damage. With the retrograde procedure there was significantly improved recovery of left ventricular function, uniform myocardial cooling and better preservation of cellular morphology.

Blood cardioplegia: a review and comparison with crystalloid cardioplegia

The Oxford International Symposium on myocardial preservation provided an appropriate milestone and impetus to survey one aspect of operative myocardial preservation, namely blood cardioplegia, and to contrast it with the more popular crystalloid cardioplegia. This review is by no means complete or exhaustive but represents my best effort to summarize important information that has accumulated in the literature as blood cardioplegia, and our understanding of it, has evolved. It is appropriate to compare blood and crystalloid cardioplegia with respect to biochemical and physiological differences. Clinical comparison has been limited, for the most part, to randomized studies, and a number of differences and details of clinical management of the two techniques have been omitted, either because they seemed unimportant or there was no good information that would allow an objective comparison of their significance. Hopefully, the reader will recognize the intent to focus on meaningful differences and similarities between the two techniques and to present them fairly.

Cardioplegia by way of the coronary sinus for valvular and coronary surgery

Retrograde coronary sinus perfusion has recently reemerged as an attractive means of delivering cardioplegic solutions during open heart procedures. In patients undergoing aortic valve or aortic root surgery, there is no evidence that coronary sinus cardioplegia results in a better myocardial protection than that achieved with the use of standard methods of anterograde cardioplegia delivery. However, the retrograde approach provides distinct technical advantages that might favor its use as an alternative to direct coronary ostial cannulation. In select subgroups of patients undergoing coronary bypass procedures, there is a growing body of evidence that the coronary sinus route may be more effective than the anterograde route because of its superior capacity to ensure homogeneous distribution of cooling and cardioplegia in myocardial areas supplied occluded arteries. The well established safety of coronary sinus cardioplegia in the clinical setting further justifies its inclusion among techniques for ensuring adequate myocardial preservation during surgically induced ischemic arrest.

Percutaneous cooling of ischemic myocardium by hypothermic retroperfusion of autologous arterial blood: effects on regional myocardial temperature distribution and infarct size

The effects of synchronized coronary venous retroperfusion of cooled autologous arterial blood on regional myocardial temperature distribution and infarct size were studied in open chest dogs with 3.5 h of left anterior descending coronary artery occlusion. After 30 min of occlusion, the dogs were randomly assigned to one of three groups: 1) untreated control group (n = 5), 2) normothermic retroperfusion group (infusion temperature 32 degrees C) (n = 7), and 3) hypothermic retroperfusion group (infusion temperature 15 degrees C) (n = 7). Regional myocardial temperatures were measured by using needle-tipped thermistors stabbed in the 1) anterior wall distal to the occlusion site, 2) anterior wall proximal to the occlusion site, 3) left lateral wall, 4) posterior wall, and 5) right ventricular free wall. Rectal and pulmonary artery temperatures were also measured. In the hypothermic retroperfusion group, the anterior wall temperature decreased rapidly by 5 degrees C at 15 min of retroperfusion (p less than 0.05 vs. normothermic retroperfusion or untreated control groups), whereas the temperature at other sites decreased with a linear trend over time. Myocardial temperatures in the ischemic area (distal anterior wall) were generally lower than those in the other sites during the first 60 min of hypothermic retroperfusion and the largest intramyocardial temperature difference (3.6 degrees C) was found at 15 min after retroperfusion. Infarct size expressed as a percent of the risk area was significantly smaller in the hypothermic retroperfusion group (6.2 +/- 3.3%) than in the control (64.9 +/- 14%) or normothermic retroperfusion groups (24.1 +/- 6.7%).(ABSTRACT TRUNCATED AT 250 WORDS)

Efficacy of coronary sinus cardioplegia in patients with complete coronary artery occlusions

Myocardial areas distal to complete coronary artery occlusions are poorly protected by antegrade cardioplegia. We assessed the effects of coronary sinus cardioplegia in 30 patients undergoing bypass operations and at high risk of cardioplegic maldistribution because of the following anatomical patterns of coronary artery disease: critical (greater than or equal to 50%) stenosis of the left main trunk with total occlusion of the right coronary artery (16 patients) or critical (greater than or equal to 70%) stenosis of the right coronary artery with total occlusion of the left anterior descending (11 patients) or circumflex artery (3 patients). After induction of arrest through the aorta, coronary sinus cardioplegia was given intermittently during the cross-clamp period at a flow rate of 100 mL/min. Intraoperatively, occluded arteries were consistently found to be filled with the retrogradely infused solution. One patient died early postoperatively of low cardiac output and a second patient died later during his hospital stay, presumably of an arrhythmia. At autopsy, none of them had pathological evidence of inadequate myocardial protection. One patient sustained a myocardial infarction and 3 others required inotropes for more than 24 hours postoperatively. Postoperative values for right and left stroke volume indices were not significantly different from prebypass levels. Overall, these results are consistent with the occurrence of limited intraoperative ischemic damage and, by inference, suggest the efficacy of the coronary sinus route in preserving myocardial areas supplied by completely occluded coronary arteries and, hence, in jeopardy of inadequate cardioplegia delivery.

Superiority of retrograde cardioplegia after acute coronary occlusion

Because antegrade cardioplegia may limit the distribution of cardioplegia beyond a coronary occlusion, this study was undertaken to determine whether retrograde coronary sinus cardioplegia provides superior myocardial protection during revascularization of an acute coronary occlusion. In 20 adult pigs, the second and third diagonal branches were occluded with a snare for 1 1/2 hours. Animals were then placed on cardiopulmonary bypass and underwent 30 minutes of ischemic arrest with multidose, potassium, crystalloid cardioplegia. In 10 animals, the cardioplegia was given antegrade through the aortic root, whereas in 10 others, it was given retrograde through the coronary sinus. After the arrest period, the coronary snares were released and all hearts were reperfused for 3 hours. Postischemic damage in the myocardium beyond the occlusions was assessed by wall motion scores using two-dimensional echocardiography (4 = normal to -1 = dyskinesia), the change in myocardial pH from preischemia, and the area of necrosis/area of risk (histochemical staining). Hearts protected with retrograde coronary sinus cardioplegia had less tissue acidosis (change in pH = 0.08 +/- 0.03 versus 0.41 +/- 0.13; p less than 0.05), higher wall motion scores (2.0 +/- 0.6 versus 1.3 +/- 0.3; not significant), and less myocardial necrosis (43.4% +/- 3.6% versus 73.3% +/- 3.5%; p less than 0.0001). We conclude that retrograde coronary sinus cardioplegia provides more optimal myocardial protection than is possible with antegrade cardioplegia after revascularization of an acute coronary occlusion.

Intraoperative assessment of regional myocardial perfusion using quantitative myocardial contrast echocardiography: an experimental evaluation

To test the hypothesis that myocardial contrast echocardiography can be used to quantitate regional myocardial flow in the arrested heart at the time of delivery of cardioplegic solution, data were acquired in 13 dogs on cardiopulmonary bypass. Different degrees of stenosis were placed in random order on the left anterior descending coronary artery. For each stenosis, myocardial contrast echocardiography was performed by injecting sonicated albumin microbubbles into the cross-clamped aortic root at the time of delivery of cardioplegic solution. The resultant echocardiographic images were analyzed on an off-line computer. Background-subtracted time-intensity plots were generated, and an exponential function, f(t) = Ce-alpha t + De- beta t, was applied to each plot. Variables that reflected the total number of microbubbles entering the coronary artery bed, such as the area under the curve and the peak height of the curve, correlated best with radiolabeled microsphere-measured myocardial flow (r = 0.92 and r = 0.91, respectively). Variables that reflected the appearance of contrast microbubbles in the myocardium, such as the initial slope and the slope at 1 s, also had a good correlation with myocardial flow (r = 0.84 and r = 0.89, respectively). Variables that reflected the washout of contrast medium from the myocardium, such as the slope of the descending portion of the curve, had only a fair correlation with myocardial flow (r = 0.65). In six dogs, the technique of injecting contrast medium into the cross-clamped aortic root was also examined. Although continuous infusion of contrast medium produced smaller perturbations in mean aortic and distal left anterior descending artery pressures compared with a bolus injection (p less than 0.01), the correlation between the variables of the time-intensity curves and flow was equally close with both techniques. It is concluded that it is possible to quantitate myocardial flow by using myocardial contrast echocardiography at the time of delivery of cardioplegic solution in dogs on cardiopulmonary bypass. The implementation of this technique in humans might be useful in guiding the sequence of graft placement and thereby improving myocardial preservation during coronary artery bypass operations.

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.

Intraoperative assessment of myocardial perfusion using contrast echocardiography

Myocardial contrast echocardiography is a new technique capable of assessing regional myocardial perfusion in vivo in real time. This article reviews the background, principles, experimental validation, and clinical uses of intraoperative myocardial contrast echocardiography. Data can be derived both for online visual and computer analyses. The technique can be useful in determining the sequence of bypass graft placement and the success of graft anastamoses. Anastamoses can be revised immediately if needed. It is hoped that this technique will improve intraoperative myocardial preservation and will diminish the rate of perioperative myocardial infarction.

Effects of atrial cardioplegia on the ischemic right ventricle after acute coronary artery occlusion and reperfusion

Right atrial cardioplegia has been advocated as a simple method of delivering retrograde cardioplegia. Passive distention of the right heart inherent with right atrial cardioplegia has been shown to impair right ventricular function in a canine model of global ischemia. This study was designed to compare right ventricular performance after right atrial cardioplegia administered intermittently (n = 5) and continuously (n = 5) with coronary sinus retrograde cardioplegia (n = 5) and aortic root cardioplegia (n = 8) in a canine model of acute right ventricular ischemia and reperfusion. Right ventricular performance was assessed using the load-independent relationship of end-systolic pressure versus dimension (myocardial fiber length). Right ventricular performance was well preserved after reperfusion in those dogs protected with intermittent right atrial cardioplegia (95% of control). Results with continuous right atrial cardioplegia (66% of control) and coronary sinus retrograde cardioplegia (40% of control) demonstrated diminished postreperfusion right ventricular performance. Right ventricular performance in the group protected with aortic root cardioplegia was significantly impaired after reperfusion when compared with all retrograde groups (34% of control, p less than 0.05). In this model, postreperfusion right ventricular performance was preserved in the right atrial cardioplegia groups despite passive ventricular distention. All methods of retrograde cardioplegia resulted in superior preservation of right ventricular performance when compared with standard aortic root cardioplegia.

Protective effects of retrograde compared with antegrade cardioplegia on right ventricular systolic and diastolic function during coronary bypass surgery

The effect of retrograde cardioplegia delivered through the right atrium on right ventricular performance has not been critically examined in humans. We randomized 20 patients with right coronary artery lesions to receive cold blood cardioplegia solution either retrograde through the right atrium (group 1, n = 10) or antegradely (group 2, n = 10). The patients were similar in age, sex, severity of coronary artery disease, cross-clamp time, and completeness of revascularization. Before operation, right ventricular function was assessed by radionuclide ventriculography, and 18-24 hours after operation, right ventricular volumes and performance were assessed at a constant-paced heart rate by simultaneous hemodynamic-radionuclide measurements, before and after a fluid challenge. Intraoperative right ventricular temperatures were not different between the groups. Right ventricular volumes and ejection fractions were not different at baseline. After operation, at similar heart rates and loading conditions, there was a trend for the antegrade group to increase right ventricular end-systolic volume (p less than 0.1) whereas the retrograde group had no change in this parameter from the preoperative state. Postoperative ventricular function curves (p = NS, retrograde versus antegrade) suggest equivalent systolic performance in both groups. Right ventricular diastolic performance showed no significant differences between the two groups, suggesting no detriment to compliance due to right ventricular distension during operation. This suggests that retrograde cardioplegia adequately protects the right ventricular myocardium during bypass surgery and may be used as an alternative procedure in situations where ventricular cooling is inadequate with antegrade delivery due to severe coronary artery disease or aortic valvular disease.