Revascularization for acute regional infarct: superior protection with 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.

Use of (all-blood) miniplegia versus crystalloid cardioplegia in an experimental model of acute myocardial ischemia

PURPOSE

Several methods of myocardial protection have been used. The use of all-blood solutions modified with glutamate and aspartate has increased. Its use in situations of acute ischemia provides improved contractile function, "resuscitating" the previously lesioned muscle. The dilution preconized by literature is around 25% of the hematocrit. The present study evaluates an all-blood cardioplegia solution with tepid 1% dilution, denominated miniplegia.

MATERIAL AND METHOD

Pigs of the Large-White breed were used with an isolated heart and perfused with blood of a support animal. Three groups (n = 7 per group) were designated with the following treatments: Control group (CO), St. Thomas solution (ST), continuous normothermic all-blood solutions (SG). After the stabilization period, systolic pressure (PS), diastolic pressure (PD), developed pressure (PD), stress of the wall, elastance, and passive stiffness were recorded. The hearts were submitted to 30 minutes of regional ischemia with the clamping of the anterior interventricular artery, and subsequently to 90 minutes of global ischemia with the use of the three different treatments during this period. At the beginning of global ischemia, the coronary clamp was removed. The hearts were again reperfused. Upon three minutes into reperfusion the hearts were defibrillated when necessary. Measurements were taken every 30 minutes to 90 minutes into reperfusion.

RESULTS

The SG presented a better recovery of the ventricular function in several of the parameters recorded. The ST group was inferior to the SG group, which in turn was superior to the CO group in some of the parameters analyzed. A higher number of defibrillations were needed to reestablish coordinated heart beats in the ST and CO groups. There were no differences related to the percentage of wet weight between the SG and ST groups, and the percentage was higher in the CO group.

CONCLUSION

The use of all-blood miniplegia provided superior protection when compared to global ischemia or crystalloid cardioplegia in acutely ischemic hearts. The model employed is very close to the clinical situation due to the use of blood as a perfusate.

Augmenting cardiac contractility hastens myocardial edema resolution after cardiopulmonary bypass and cardioplegic arrest

Although myocardial edema is associated with cardiopulmonary bypass (CPB) and cardioplegic arrest (CPA), interventions to expedite edema removal have not been investigated. The primary mechanism for the removal of excess interstitial fluid in the heart is myocardial lymphatic drainage, but lymphatic function can be impaired by decreased contractility because of edema. The purpose of this study was to determine whether enhancing cardiac contractility would increase myocardial lymphatic function and hasten edema resolution after CPB. Sixteen dogs were subjected to CPB and 1 h of hypothermic CPA. After weaning from CPB, 10 dogs received an intravenous dobutamine infusion and 6 dogs received no inotropic support. We determined myocardial lymph driving pressure from the major cardiac lymphatic, myocardial water content by using microgravimetry, and the peak rate of left ventricular pressure increase (dP/dmax) by using micromanometry. Measurements were taken at baseline, during CPA, and 60 min after CPB. Compared with controls, dobutamine-treated dogs had an increased dP/dmax (P < 0.05), which was associated with higher lymph driving pressures (P < 0.05), resulting in lower myocardial water gain 1 h after CPB (P < 0.05). We conclude that the resolution of myocardial edema after CPB was hastened by dobutamine. Organized ventricular contraction and myocardial contractility seem to be important determinants of myocardial lymphatic function and myocardial edema removal. These findings suggest that the administration of inotropic drugs after CPB may hasten cardiac recovery.

IMPLICATIONS

Myocardial edema, which develops during cardiopulmonary bypass and cardioplegic arrest, contributes to cardiac dysfunction after heart surgery. This study demonstrated that enhancement of cardiac contractility by the administration of dobutamine after cardiopulmonary bypass and cardioplegic arrest was associated with increased myocardial lymphatic function and hastened edema resolution in dogs.

Comparative effects of continuous warm blood and intermittent cold blood cardioplegia on coronary reactivity

BACKGROUND

Cardioplegia is known to affect coronary vascular reactivity. We examined the effects of intermittent cold and continuous warm blood cardioplegia on beta-adrenoceptor-mediated, adenosine triphosphate-sensitive K+ (K+ATP)-channel-mediated, and endothelium-dependent relaxation and on the myogenic tone of coronary arterioles.

METHODS

Pigs were placed on cardiopulmonary bypass. Hearts were arrested for 1 hour with a cold blood cardioplegic solution administered intermittently (n = 12; iCB-CP) or with a warm blood cardioplegic solution delivered continuously (n = 12; cWB-CP). Selected hearts (n = 6 in each group) were then reperfused for 1 hour. In vitro relaxation responses of precontracted microvessels (50 to 160 microns) were studied in a pressurized no-flow state.

RESULTS

Relaxation in response to isoproterenol (beta-adrenergic agonist) was similar after iCB-CP and cWB-CP, whereas forskolin (adenylate cyclase activator)-induced relaxation was impaired more after iCB-CP than after cWB-CP. After reperfusion the respective responses were similar. Both iCB-CP and cWB-CP preserved receptor-mediated, endothelium-dependent relaxation in response to adenosine, 5'-diphosphate; non-receptor-mediated endothelium-dependent relaxation in response to A23187; endothelium-independent cyclic guanosine monophosphate-mediated relaxation in response to sodium nitroprusside, and K+ATP-channel-mediated relaxation. Relaxations in response to 8-bromo-cyclic guanosine monophosphate (a cyclic guanosine monophosphate-dependent protein kinase activator) and to 8-bromo-cyclic adenosine monophosphate (a cyclic adenosine monophosphate-dependent protein kinase activator) were impaired after iCB-CP alone and after reperfusion, whereas the respective responses were not affected after cWB-CP. Myogenic tone was decreased similarly after iCB-CP and cWB-CP but was not further altered after reperfusion. Cardiac function was similar after iCB-CP and cWB-CP.

CONCLUSIONS

These results suggest that cWB-CP is similar to iCB-CP in its ability to preserve endothelium-dependent relaxation and K+ATP-channel function. The superior preservation of beta-adrenergic-cyclic adenosine monophosphate-mediated coronary responses after cWB-CP is brief and associated with minimal improvement of myocardial function and myogenic tone.

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.

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.

Microvascular reactivity after crystalloid, cold blood, and warm blood cardioplegic arrest

BACKGROUND

The effects of three techniques of cardioplegic arrest on endothelium-dependent microvascular function of the right and left ventricles were examined in a canine model of cardiopulmonary bypass.

METHODS

Oxygenated cold crystalloid cardioplegia and cold blood cardioplegia groups, (n = 11 each) had hypothermic cardiopulmonary bypass (28 degrees C), topical cooling, antegrade arrest, and intermittent antegrade delivery. A warm blood cardioplegia group (n = 11) had normothermic cardiopulmonary bypass (37 degrees C), antegrade arrest, and continuous antegrade delivery. All groups underwent cardioplegic arrest for 1 hour followed by 1 hour of reperfusion. Dogs that did not have instrumentation were used as controls (n = 10). Coronary microvessels (100 to 200 microns in internal diameter) were examined in a pressurized, no-flow state with video microscopic imaging and electronic dimension analysis.

RESULTS

Ischemic arrest with cold crystalloid cardioplegia significantly (p < 0.05) impaired endothelium-dependent relaxations in both ventricles to acetylcholine (left ventricle, 69% +/- 4%, and right ventricle, 73% +/- 5%, versus control left ventricle, 100% +/- 0.3%, and control right ventricle, 100% +/- 0.3%) and the calcium ionophore (left ventricle, 70% +/- 6%, and right ventricle, 68% +/- 3%, versus control left ventricle, 98% +/- 1%, and control right ventricle, 98% +/- 1%). In the cold blood cardioplegia group, endothelium-dependent relaxations to acetylcholine (left ventricle, 96% +/- 1%, and right ventricle, 87% +/- 4%) and the calcium ionophore (left ventricle, 88% +/- 3%, and right ventricle, 78% +/- 7%) were preserved. In the warm blood cardioplegia group, endothelium-dependent responses to acetylcholine (92% +/- 3%) and the calcium ionophore (96% +/- 1%) were preserved in the left ventricle, but the right ventricle showed reduced (p < 0.05) reactivity to the endothelium-dependent acetylcholine (77% +/- 8%) and the calcium ionophore (69% +/- 8%). Endothelium-independent relaxation to sodium nitroprusside was similar to controls in all groups for both ventricles, thus indicating normal smooth muscle responsiveness.

CONCLUSIONS

Cardioplegic arrest with cold blood cardioplegia preserved the endothelium-dependent response in the right and left ventricles, whereas cold crystalloid cardioplegia impairs this response. Warm blood cardioplegia preserved the endothelium-dependent response in the left ventricle, but this response was reduced in the right ventricle. This suggests that blood cardioplegia and hypothermia may be important in protection of microvascular endothelium and that the right ventricle may be more vulnerable to damage than the left ventricle.

A critical assessment of neurological risk during warm heart surgery

A prospective randomized trial comparing retrograde warm blood cardioplegia with cold oxygenated crystalloid cardioplegia in coronary bypass patients at Emory University revealed an increased risk of adverse neurological events in the warm group (4.5% vs 1.4%, p < 0.005). Multivariant analysis found four variables to be independent predictors of adverse neurological outcome: congestive heart failure (p = 0.002); age (p = 0.002); aortic cross-clamp time (p = 0.02); and randomization to the warm group (p = 0.026). In Toronto, a prospective randomized trial compared antegrade warm blood cardioplegia with antegrade cold blood cardioplegia. Compared to the Emory trial, the Toronto series contained fewer female patients (16% vs 25%), fewer patients older than age 70 (16% vs 30%), and fewer redo operations (4% vs 14%). The other prominent differences between the Emory series and the Toronto series were: extensive use of retrograde cardioplegia in the Emory series; mild hypothermia in the warm group in the Toronto series; and elevated serum glucose in the warm group in the Emory series. The Toronto series showed no difference in adverse neurological events comparing cold versus warm cardioplegia groups. A comparison of these two series suggests that mild hypothermia in the Toronto series, elevated glucose in the Emory series, or the use of retrograde cardioplegia may be operative in the elevated incidence of adverse neurological events seen in the Emory series in addition to a relatively larger number of high-risk patients (female, elderly, and redo) in the Emory series.

Neurologic events after coronary bypass grafting: further observations with warm cardioplegia

Warm heart surgery has documented myocardial protection benefit, but with an added neurologic threat. It is hypothesized that moderately hypothermic aerobic heart surgery will maintain the myocardial protection and reduce neurologic risk. This study compared 493 patients undergoing coronary artery bypass graft operations with normothermic (35 degrees to 37% degrees C) continuous blood cardioplegia and normothermic perfusion to 379 coronary artery bypass grafting patients with hypothermic (33 degrees to 29 degrees C) continuous blood cardioplegia and hypothermic perfusion to test this hypothesis. There was no difference in age, sex, prior myocardial infarction, hypertension, prior neurologic event, congestive failure, or diabetes. The hypothermic group had more reoperations (24% versus 14%; p = 0.0002), class III/IV angina (83% versus 71%; p = 0.002), a trend to more triple-vessel (54% versus 47%; p = 0.10) and left main disease (18% versus 14%; p = 0.10), lower ejection fractions (0.52 +/- 0.15 versus 0.55 +/- 0.13), more grafts placed (3.6 +/- 1.1 versus 3.4 +/- 1.1; p = 0.04), but fewer internal mammary arteries (62% versus 78%; p < 0.0001). Postoperative myocardial infarction rate was 1.2% in the hypothermic group and 1.3% in the normothermic group (p = not significant). Intraaortic balloon pump requirement was 3.4% with hypothermic and 1.4% with normothermic groups (p = 0.05). The incidence of postoperative neurologic events was significantly higher in the normothermic group (4.7% versus 1.8%; p = 0.038). The multivariate correlates of stroke were older age and normothermic cardioplegia, whereas the only multivariate correlate of death was older age.(ABSTRACT TRUNCATED AT 250 WORDS)

Functional recovery after ischemia: warm versus cold cardioplegia

Warm continuous retrograde cardioplegia has been introduced for myocardial protection during cardiac operations, particularly in the setting of acute myocardial ischemia because of its theoretical advantage of producing arrest without ischemia. To investigate the ability of warm continuous retrograde cardioplegia to provide myocardial protection after acute global ischemia, versus the more commonly used cold intermittent antegrade cardioplegia, 12 dogs were subjected to 15 minutes of normothermic global myocardial ischemia on cardiopulmonary bypass followed by 75 minutes of protected cardioplegic arrest using either warm continuous retrograde cardioplegia or cold intermittent antegrade cardioplegia. Standard blood cardioplegia at clinically used volumes and flow rates was used. Warm continuous retrograde cardioplegia animals received 30 mL/kg antegrade to induce arrest followed by 1.5 to 1.8 mL.kg-1.min-1 retrograde at 37 degrees C, whereas cold intermittent antegrade cardioplegia animals received 30 mL/kg antegrade to induce arrest followed by 15 mL/kg antegrade every 15 minutes at 10 degrees C. Load-insensitive left ventricular systolic function, diastolic function, high energy nucleotides, and edema formation were assessed before and after ischemia. Results showed that myocardial preservation using clinically reported flow rates and volumes of warm continuous retrograde cardioplegia was significantly inferior to that provided by clinically used cold intermittent antegrade cardioplegia, as demonstrated by decreased preload recruitable stroke work slope (28 +/- 11 versus 71 +/- 6), increased alpha constant of the end diastolic stress-strain relationship (14.2 +/- 3.0 versus 3.6 +/- 1.0), decreased total nondiffusable nucleotides (40.7 +/- 2.3 versus 57.4 +/- 2.3 microM/g wet weight) and increased water content (82.2% +/- 0.4% versus 80.4% +/- 0.4%).(ABSTRACT TRUNCATED AT 250 WORDS)

Aerobic blood cardioplegia for revascularization of acute infarct: effects of delivery temperature

The effects of different cardioplegia temperatures on myocardial protection with continuous aerobic blood cardioplegia were studied in a canine model of acute regional injury after left anterior descending coronary artery occlusion and subsequent revascularization. Twenty-five animals underwent 90 minutes of occlusion followed by revascularization during 60 minutes of electromechanical arrest with continuous retrograde blood cardioplegia delivered at one of three temperatures: 18 degrees C (n = 8), 28 degrees C (n = 8), and 37 degrees C (n = 9). Left ventricular protection was assessed in a right heart bypass model in terms of the left ventricular pressure-volume relationships, myocardial oxygen consumption, regional myocardial blood flow, adenosine trisphosphate concentration, and water content. The preload recruitable stroke work relationship at 90 minutes after reperfusion was better in the 18 degrees C and 28 degrees C groups than that in the 37 degrees C group (18 degrees C, 85 +/- 14 erg x 10(3)/mL; 28 degrees C, 77 +/- 17 erg x 10(3)/mL; 37 degrees C, 58 +/- 13 erg x 10(3)/mL; p < 0.05). The maximum elastance and stress-strain relationships showed there were no significant differences between the groups at 90 minutes. The myocardial oxygen consumption was greatest in the 37 degrees C group during the first hour after reperfusion (18 degrees C, 5.4 +/- 1.4 mL O2.min-1.100 g-1; 28 degrees C, 4.7 +/- 1.1 mL O2.min-1.100 g-1; 37 degrees C, 6.3 +/- 1.6 mL O2.min-1.100 g-1; p < 0.05). The regional myocardial blood flow, adenosine triphosphate concentration, and myocardial water content were similar in the three groups.(ABSTRACT TRUNCATED AT 250 WORDS)