Warm heart surgery and results of operation for recent myocardial infarction

Novel Strategies to Improve the Cardioprotective Effects of Cardioplegia

The use of cardioprotective strategies as adjuvants of cardioplegic solutions has become an ideal alternative for the improvement of post-surgery heart recovery. The choice of the optimal cardioplegia, as well as its distribution mechanism, remains controversial in the field of cardiovascular surgery. There is still a need to search for new and better cardioprotective methods during cardioplegic procedures. New techniques for the management of cardiovascular complications during cardioplegia have evolved with new alternatives and additives, and each new strategy provides a tool to neutralize the damage after ischemia/reperfusion events. Researchers and clinicians have committed themselves to studying the effect of new strategies and adjuvant components with the potential to improve the cardioprotective effect of cardioplegic solutions in preventing myocardial ischemia/reperfusion-induced injury during cardiac surgery. The aim of this review is to explore the different types of cardioplegia, their protection mechanisms, and which strategies have been proposed to enhance the function of these solutions in hearts exposed to cardiovascular pathologies that require surgical alternatives for their corrective progression.

Theoretical and Practical Aspects in the Use of Bretschneider Cardioplegia

The race for an ideal cardioplegic solution has remained enthusiastic since the beginning of the modern cardiac surgery era. The Bretschneider solution, belonging to the “intracellular cardioplegic” group, is safe and practical in myocardial protection during ischemic time. Over time, some particular concerns have arisen regarding the effects on cardiac metabolism and postoperative myocardial functioning. This paper reviews the most important standpoints in terms of theoretical and practical analyses.

Myocardial protection in cardiac surgery: how limited are the options? A comprehensive literature review

For patients undergoing cardiopulmonary bypass, myocardial protection is a key for successful recovery and improved outcomes following cardiac surgery that requires cardiac arrest. Different solutions, components and modes of delivery have evolved over the last few decades to optimise myocardial protection. These include cold and warm and blood and crystalloid solution through antegrade, retrograde or combined cardioplegia delivery approach. However, each method has its own advantages and disadvantages, posing a challenge to establish a gold-standard cardioplegic solution with an optimised mode of delivery for enhanced myocardial protection during cardiac surgery. The aim of this review is to provide a brief history of the development of cardioplegia, explain the electrophysiological concepts behind myocardial protection in cardioplegia, analyse the current literature and summarise existing evidence that warrants the use of varying cardioplegic techniques. We provide a comprehensive and comparative overview of the effectiveness of each technique in achieving optimal cardioprotection and propose novel techniques for optimising myocardial protection in the future.

Optimal Conditions for Cardiopulmonary Bypass

There is no single optimal set of conditions for cardio pulmonary bypass. What is optimal is determined by patient factors, surgical need, and the mechanics of perfusion. Additionally, the best way to manage bypass typically varies over its course.

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 the Cobra catheter for targeted temperature management during cardiopulmonary bypass in swine

BACKGROUND

The purpose of this investigation was to determine whether temperatures of the aortic arch and descending aortic circulations could be controlled independently during cardiopulmonary bypass with a cannula possessing an endoaortic baffle (Cobra; Cardeon, Cupertino, Calif).

METHODS

After Institutional Animal Care and Use Committee approval, 12 pigs weighing 60 kg were started on bypass through a sternotomy. A dual-lumen endoaortic cannula with a deployable baffle was used for arterial cannulation. Bypass was initiated at 37 degrees C, and control measurements were obtained. The baffle was then inflated with saline solution, segmenting blood flow along the greater and lesser curvatures of the aortic arch. Parallel heat exchangers were used to independently control temperature of the arch and descending aortic perfusates. Cerebral and systemic temperatures were recorded continuously.

RESULTS

During cardiopulmonary bypass, mean flow and arterial pressure were maintained at 2.4 to 2.6 L x min(-1) x m(-2) and 60 to 70 mm Hg, respectively. With aortic flow distributed by the baffle, a 5 degrees C temperature differential between brain (30 degrees C) and body (35 degrees C) was established in a mean of 5 +/- 2 minutes. Mean brain and corporeal temperatures of 27 degrees C and 35 degrees C were then maintained over 60 minutes. Relative to control, internal jugular and inferior vena cava oxygen saturations increased during targeted temperature control with the device.

CONCLUSIONS

The Cobra cannula allows for independent control of brain and body temperature while providing satisfactory hemodynamics. Application of this temperature management strategy may offer cerebral protection and the advantages of warm systemic bypass temperature.

Differential perfusion: a new technique for isolated brain cooling during cardiopulmonary bypass

BACKGROUND

The purpose of this study was to determine the feasibility of differential perfusion of the aortic arch and descending aorta during cardiopulmonary bypass using a cannula designed for aortic segmentation.

METHODS

Pigs weighing 57 kg (n = 8), underwent cardiopulmonary bypass using the dual lumen aortic cannula. An inflatable balloon separated proximal (aortic arch) and distal (descending aorta) ports. During differential perfusion, the aorta was segmented and the arch and descending aorta perfused differentially using parallel heat exchangers. Ability to independently control brain and body temperature, cardiopulmonary bypass flow rate and mean arterial blood pressure was determined.

RESULTS

During differential perfusion cerebral hypothermia (27 degrees C) with systemic normothermia (38 degrees C) was established in 23 minutes. Independent control of arch and descending aortic flow and mean arterial blood pressure was possible. Analysis of internal jugular venous O2 saturation data indicated an increase in the ratio of cerebral O2 supply to demand during differential perfusion.

CONCLUSIONS

A cannulation system segmenting the aorta allows independent control of cerebral and systemic perfusion. This device could provide significant cerebral protection while maintaining the advantages of warm systemic cardiopulmonary bypass temperatures.

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.

Beyond hyperkalemia: beta-blocker-induced cardiac arrest for normothermic cardiac operations

BACKGROUND

Four experimental protocols were carried out to assess the ability of esmolol to induce and maintain reversible cardiac arrest under continuous normothermic (37 degrees C) perfusion.

METHODS AND RESULTS

In the first protocol, 8 perfused rat hearts were subjected to 20, 60, 90, and 120 minutes of esmolol arrest, after which positive and negative first derivative of pressure, heart rate, left ventricular developed pressure, and left ventricular end-diastolic pressure were evaluated. Arrest was achieved 45 to 60 seconds after beginning the infusion of esmolol. Mechanical arrest was achieved before electrical arrest. In the second protocol, dose-response curves were obtained using isolated (Langendorff) rat and rabbit (n = 6) hearts. The concentrations of esmolol varied from 0.084 to 6.7 mmol/L and from 0.12 to 1.45 mmol/L in the rat and rabbit heart experiments, respectively. In the third protocol, the effects of 20 minutes of normothermic (37 degrees C) ischemia on the function of isolated rat hearts perfused with esmolol-containing Krebs solution were compared with those using high-potassium (25 mmol/L) Krebs solution. Group A subjects (n = 9) received the ischemic injury after being perfused (and arrested) for 20 minutes with either esmolol or potassium (KCl, 25 mmol/L). Group B subjects (n = 10) received the same ischemic insult before being perfused with either esmolol or potassium. Esmolol-treated hearts showed better recovery than those receiving potassium, in terms of +/- dP/dt (p < 0.01), left ventricular systolic pressure (p < 0.01), and left ventricular developed pressure (p < 0.009). Finally, the fourth protocol was done to evaluate the effects of esmolol in a clinically relevant experimental model. Pigs were divided into esmolol (n = 6) and potassium (n = 5) groups and subjected to normothermic cardiopulmonary bypass and a 1-hour period of cardiac arrest. Twenty minutes after stopping infusion of the cardioplegic agents, all animals were weaned off bypass. There were no statistically significant differences between the groups.

CONCLUSIONS

Esmolol hydrochloride can be used as effectively as potassium for inducing and maintaining predictable and reversible cardiac arrest during normothermic cardiac operations.

The effects of cardiopulmonary bypass temperature on neuropsychologic outcome after coronary artery operations: a prospective randomized trial

The effect of systemic perfusion temperature on postoperative cognitive function was investigated in 96 adult patients undergoing elective coronary revascularization with cardiopulmonary bypass at 28 degrees C, 32 degrees C, or 37 degrees C. Neuropsychologic performance was assessed 1 day before the operation and 6 weeks after the operation. Five tests were adapted from the Wechsler Adult Intelligence Scale and two from the Wechsler Memory Scale.

RESULTS

No patients had major neurologic complications. Ninety-three patients completed the five Wechsler Adult Intelligence Scale tests, but only 70 went on to complete the Wechsler Memory Scale tests as well. In these, there was an effect of cardiopulmonary bypass temperature on the number of neuropsychologic tests in which there was a preoperative to postoperative deterioration (p = 0.021), the number with bypass at 37 degrees C being significantly greater than the number with bypass at 32 degrees C (p = 0.015). Subsidiary analyses using a multivariate linear model examined the effect of cardiopulmonary bypass temperature on the magnitude of change, with or without allowing for other possible confounding influences. There was an adverse effect of normothermic (37 degrees C) versus moderately hypothermic (32 degrees C) perfusion---more convincingly displayed in the analyses of all seven scores rather than just the Wechsler Adult Intelligence Scale scores. Further cooling to 28 degrees C conferred no additional benefit in terms of cognitive function. The importance of the deterioration is open to question.

Normothermic Cardiopulmonary Bypass

Normothermic cardiopuhnonary bypass avoids the detrimental systemic effects of hypothermia. It is a safe and effective technique of systemic perfusion during cardiopulmonaiy bypass. Myocardial preservation is not compromised when electromechanical quiescence is maintained. Cerebral protection is comparable to that of systemic hypothermia. Low vascular resistance is common and easily treated with higher perfusion flows or vasopressors during bypass and facilitates weaning from bypass. Duration of cardiopulmonary bypass is significantly shortened by the absence of systemic cooling and rewarming phases. Clinical outcomes of patients undergoing cardiac, surgery with normothermic bypass compare favorably with those receiving moderate hypothermia.

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.

Protective effect of nicorandil as an additive to the solution for continuous warm cardioplegia

Experiments were designed to assess whether (1) nicorandil given before global low-flow ischemia or (2) included in low-flow continuous cardioplegia improved the recovery of cardiac function in the isolated rat heart. The first investigated the effect of nicorandil (2, 10, or 100 mumol/L), given for 3 minutes before 30 minutes of normothermic global ischemia, on recovery after 30 minutes of reperfusion. In aerobically perfused hearts, doses of 10 and 100 mumol/L significantly increased coronary flow; the dose of 100 mumol/L exerted a negative inotropic effect. These doses shortened the time to contractile arrest (282 +/- 18 and 276 +/- 22 seconds versus 354 +/- 16 seconds in the control hearts with unmodified ischemia; p < 0.05 in both instances). Nicorandil also improved the postischemic recovery of coronary flow (79.1% +/- 1.7% and 78.0% +/- 1.6%, respectively, versus 71% +/- 1.8%; p < 0.05). However, there was no significant improvement in recovery of contractile function, creatine kinase leakage, or tissue adenosine triphosphate and creatine phosphate contents. Second, pretreatment with nicorandil (10 mumol/L) was shown to increase susceptibility of the hearts to reperfusion-induced ventricular fibrillation from 0% (n = 8) in control hearts to 50% in the drug-treated group (p < 0.05). Third, nicorandil (10 mumol/L) was added to cardioplegic and noncardioplegic solutions infused into the coronary tree throughout 100 minutes of low-flow (0.7 ml/min) ischemia: in eight of nine control hearts electrical activity was maintained throughout, whereas in all nicorandil-treated hearts electrical activity was suppressed for at least part of the time. Nicorandil also reduced the prevalence of ischemic contracture to 0% during continuous infusion of cardioplegic solution (compared with 30% in nicorandil-free control hearts) and improved the recovery of contractile function after 40 minutes of reperfusion. Thus, in the noncardioplegia groups, left ventricular developed pressure recovered to 77.8% +/- 4.0% versus 51.7% +/- 2.6% in control hearts (p < 0.05) and in the cardioplegia groups to 96.2% +/- 4.2% versus 79.7% +/- 5.5% (p < 0.05). Ventricular compliance (the ventricular volume required to achieve a left ventricular end-diastolic pressure of 4 mm Hg) was better preserved in the nicorandil-containing noncardioplegia group (133 +/- 6 microliters) than in the control group (88 +/- 10 microliters; p < 0.05). In conclusion, nicorandil has been shown to (1) reduce ischemic contracture, (2) lessen the effects of ischemic arrest, and (3) improve the postischemic recovery of contractile function. In this species and preparation it may, however, enhance vulnerability to reperfusion-induced arrhythmias.

Normothermic versus mild hypothermic retrograde blood cardioplegia: a prospective, randomized study

BACKGROUND

Continuous retrograde blood cardioplegia has been introduced as a promising alternative for myocardial protection during cardiac operations, although the optimal conditions for its delivery have been poorly studied.

METHODS

We randomized a prospective series of 101 patients to receive either retrograde warm (37 degrees C) or mild hypothermic (28 degrees to 29 degrees C) blood cardioplegia during elective coronary artery bypass grafting. Warm blood cardioplegia was delivered to the aortic root until the heart was arrested, after which the regimen was switched to retrograde and continued either as warm or mild hypothermic cardioplegia. Oxygen consumption and transcardiac pH differences during aortic cross-clamping were determined, and postoperative creatine kinase-MB efflux, hemodynamic recovery, and clinical complications monitored.

RESULTS

Clinical characteristics, cardioplegia delivery rates, aortic cross-clamp and cardiopulmonary bypass times, and the number of distal anastomoses were similar in both patient groups. Short intermissions in cardioplegia delivery during construction of distal anastomoses were allowed, the ischemia time in the mild hypothermic group being somewhat longer (8.3% +/- 1.1% versus 5.1% +/- 0.8% of cross-clamp time; p = 0.05). Myocardial oxygen consumption was lower in the mild hypothermic group (2.49 +/- 0.23 versus 3.93 +/- 0.33 mL/min at 30 minutes of cross-clamping; p < 0.01), and the transcardiac pH difference was smaller (0.05 +/- 0.01 versus 0.07 +/- 0.01 at 30 minutes of cross-clamping; p < 0.03). Postoperative creatine kinase-MB levels were higher in the normothermic group. Heart rate was higher and left ventricular stroke work index smaller in the warm group, but otherwise there were no major differences between the groups in hemodynamic recovery. The number of postoperative complications was also similar in both groups.

CONCLUSIONS

Although both normothermic (37 degrees C) and mild hypothermic (28 degrees to 29 degrees C) retrograde blood cardioplegia, when delivered in near-continuous fashion, will offer safe myocardial protection during coronary artery bypass grafting, mild hypothermia seemed to provide somewhat better protection under the conditions prevailing here. The effects of different cardioplegia temperatures should perhaps be tested further in patients with recent myocardial infarction, unstable angina, or severely depressed left ventricular function.

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.

The physiologic basis of warm cardioplegia

BACKGROUND

Advances in myocardial protection have been instrumental in making cardiac surgery safer. Debate exists over the optimal medium and the optimal temperature for cardioplegia. Currently blood cardioplegia is preferred over crystalloid; the optimal temperature, however, remains controversial.

METHODS

Both warm and cold blood cardioplegia use potassium-induced electromechanical arrest, thereby reducing oxygen consumption by 90% in the working heart. Hypothermic blood cardioplegia given every 15 to 30 minutes provides a bloodless operative field and reduces oxygen consumption an additional 5% to 20%. Continuous warm cardioplegia avoids the deleterious effects of hypothermic ischemia and minimizes reperfusion injury. Perfusion is often interrupted for 5 to 10 minutes to allow adequate visualization of the operative site. Both warm and cold cardioplegia can be given either antegrade or retrograde.

RESULTS

Retrospective studies from Toronto support the safety and efficacy of warm cardioplegia. Two large prospective, randomized trials of warm cardioplegia versus intermittent cold blood or cold crystalloid cardioplegia demonstrated equally low incidences of death, perioperative myocardial infarction, and need of intraaortic balloon pump support.

CONCLUSIONS

Warm blood cardioplegia represents the latest development in myocardial protection. Preliminary studies support its efficacy. Additional studies are needed to determine the ideal route of delivery and to identify any risks associated with the inherent warm cardiopulmonary bypass required.

Myocardial protection for coronary bypass grafting: the Toronto Hospital perspective

BACKGROUND

The contemporary results of coronary artery bypass grafting using a variety of myocardial preservation techniques are excellent. In recent years, the number of "high-risk" patients referred for operation has increased, thus necessitating continued advances in surgical myocardial protection.

METHODS

In this article, we review recent advances in clinical myocardial protective techniques and emphasize studies conducted at The Toronto Hospital. Further, on the basis of promising current research, we speculate on future prospects for myocardial protection.

RESULTS

At The Toronto Hospital, we converted from crystalloid to intermittent cold blood cardioplegia in 1985. We demonstrated that "continuous" cardioplegic strategies may help resuscitate the ischemic myocardium and reduce operative complications in high-risk patients. Further improvements in myocardial protection will require refinements in cardioplegic solution temperature, direction of delivery, and additives to "precondition" the myocardium against ischemic damage.

CONCLUSIONS

Major advances that meet the requirements of an increasingly high risk patient population have been made in surgical myocardial protection in recent years. The future is bright for continued progress in this area.

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.

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)

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

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

Is there a place for cold crystalloid cardioplegia in the 1990s?

New cardioplegic techniques have been advocated as advantageous when compared with previously accepted standard methods. This study assessed results of a recent cohort of 388 consecutive patients undergoing coronary artery bypass grafting between 1990 and 1992 using a standard cold crystalloid cardioplegia. The mean age of patients was 61.0 +/- 0.5 years; there were 324 male and 64 female patients. Risk factor distribution has not changed recently. Preoperative left ventricular dysfunction (grade III/IV) was significant in 35.1% of patients, and 63.3% had previous myocardial infarctions. Intraoperative cardiac arrest was achieved using an average of 1,254 +/- 14 mL of St. Thomas' solution in multiple doses. Patients had a mean of 3.1 +/- 0.04 grafts constructed, with 87.7% receiving at least one internal thoracic artery graft. Anoxia and total cardiopulmonary bypass times were 40.6 +/- 0.6 and 90.3 +/- 1.4 minutes, respectively. Perioperative myocardial infarction was identified in 5.7% of patients with elevated creatine kinase levels and electrocardiographic measurement changes, inotropic agents were required in 17.8%, and the intraaortic balloon was required in 3.6% of patients. Hospital stays averaged 11.2 +/- 0.5 days. Overall 30-day mortality was 1.0%, whereas those patients undergoing elective operation (n = 219) had a mortality of 0%. In conclusion, cold crystalloid cardioplegia has the advantages of being inexpensive and simple to use. These results suggest that coronary artery bypass grafting still may be performed very safely using this technique.

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)

Effects of cold and warm blood cardioplegia assessed by myocardial pH and release of metabolic markers

The optimal temperature of blood cardioplegia remains controversial. Interstitial myocardial pH was monitored online with a probe that was inserted in the anterior wall of the left ventricle. Venous pH, lactate production, and creatine kinase and troponin T release were measured in coronary sinus blood obtained in 14 dogs after ischemic arrest periods of 5, 10, 20, and 40 minutes with warm (n = 7; mean myocardial temperature, 35 degrees +/- 2 degrees C) and cold (n = 7; mean myocardial temperature, 12 degrees +/- 1 degree C) blood cardioplegic protection. Blood cardioplegic solution was delivered at a rate of 100 mL/min during the 10 minutes between each ischemic arrest. The interstitial myocardial pH decreased significantly (p < 0.05) from 7.1 +/- 0.3 to 6.53 +/- 0.3 after ischemia in animals perfused with warm blood cardioplegia and from 7.04 +/- 0.3 to 6.64 +/- 0.1 in those receiving cold blood cardioplegic protection; however, the difference between the groups was not significant (p > 0.05). Lactate production and creatine kinase and troponin T release increased significantly after ischemia, but there was no difference in the changes between the warm and cold blood cardioplegia groups. In conclusion, ischemia caused significant changes in all variables measured, and these changes were directly proportional to the duration of ischemia. However, there was no significant difference (p > 0.05) in the myocardial metabolic changes between the warm and cold blood cardioplegia groups in terms of the duration of ischemic arrest studied.(ABSTRACT TRUNCATED AT 250 WORDS)

Intermittent antegrade warm versus cold blood cardioplegia: a prospective, randomized study

A prospective, randomized study was performed in 200 patients undergoing coronary artery bypass grafting to compare the myocardial protection obtained with intermittent antegrade warm versus cold blood cardioplegia. Preoperative and surgical characteristics of the two cohorts were similar. Intermittent antegrade infusion of warm blood cardioplegia failed to achieve sustained electromechanical arrest of the heart in 13%. The only difference in clinical outcomes was the more frequent spontaneous return to sinus rhythm after the unclamping of the aorta in the warm group (88% versus 70%, p = 0.002). Mortality (1% each) and myocardial infarction (2% and 4%) rates were similar. Rates of increase in serum activity of the isoenzyme of creatine kinase (CK-MB), CK-MB mass concentration, and cardiac troponin-T level as well as total release of troponin T were significantly lower in the warm group, and fewer patients in this group had a clinically significant increase in serum CK-MB mass (20% versus 39%, p = 0.005) and troponin T (20% versus 56%, p = 0.00001). Thus, intermittent antegrade warm blood cardioplegia is appropriate and clinically safe; the lower release of biochemical markers of myocardial damage suggests improved protection during first-time coronary artery bypass grafting.

Stunned myocardium following prolonged cardiopulmonary bypass: effect of warm versus cold cardioplegia in the canine model

"Stunned myocardium" is defined as the prolonged but transient postischemic contractile dysfunction of viable myocardium that has been salvaged by reperfusion. This phenomenon, although first characterized in the experimental canine model of coronary artery occlusion/reperfusion, also occurs following transient global ischemia. Moreover, despite the superb cardioprotection conferred by administration of cold cardioplegia during aortic cross-clamping, stunned myocardium is a well-recognized sequela of prolonged cardiopulmonary bypass. Using the anesthetized open chest dog, we tested the concept that continuous retrograde infusion of warm blood cardioplegia would effectively prevent ischemia during prolonged aortic cross-clamping and thereby preclude the development of stunned myocardium following bypass. Thirteen dogs were placed on cardiopulmonary bypass and randomized to receive: (1) continuous retrograde administration of warm blood cardioplegia (n = 8); or (2) intermittent retrograde cold blood cardioplegia (n = 5) during a 3-hour cross-clamp period. Left ventricular (LV) systolic function (i.e., area LV ejection fraction and posterior LV free wall thickening assessed by two-dimensional echocardiography) and hemodynamic parameters were monitored at baseline and at 1 and 2 hours postbypass and, at the end of the protocol, transmural myocardial biopsies were obtained for electron microscopic analysis. All dogs in both treatment groups showed electron microscopic evidence of mild and reversible morphological injury indicative of stunned myocardium, with no difference between dogs that received warm versus cold cardioplegia. Direct comparison of LV function between the two groups was confounded by a profound decrease in afterload in dogs that received cold cardioplegia. However, incorporation of systemic vascular resistance as a covariate revealed that LV function following bypass was modestly depressed at approximately 85% of baseline values, and that continuous administration of warm cardioplegia did not prevent this hypokinesis. Thus, in our canine model: (1) morphological injury and LV dysfunction induced by 3 hours of aortic cross-clamping is subtle; and (2) continuous retrograde infusion of warm blood cardioplegia during the cross-clamp period failed to preclude myocardial stunning following prolonged cardiopulmonary bypass.

Stunned myocardium in warm and cold cardiac surgery

Stunned myocardium is known to occur after cardiac surgery. Although clinical data to date suggest that continuous normothermic blood cardioplegia does not result in more postoperative ventricular dysfunction, its superiority over hypothermic techniques remains controversial.

Revascularization for acute regional infarct: superior protection with warm blood cardioplegia

Continuous retrograde warm blood cardioplegia was compared with two widely used hypothermic myocardial protection techniques in a canine model of acute regional myocardial ischemia with subsequent revascularization. Animals (n = 30) underwent 45 minutes of left anterior descending coronary artery occlusion then cardioplegic arrest (60 minutes), followed by separation from cardiopulmonary bypass and data collection. The cold oxygenated crystalloid cardioplegia group (CC; n = 8) and the cold blood cardioplegia group (CC; n = 10) had cardiopulmonary bypass at 28 degrees C, antegrade arrest, and intermittent retrograde delivery. The warm blood cardioplegia group (WB; n = 12) had normothermic cardiopulmonary bypass, antegrade arrest, and continuous retrograde delivery. Overall ventricular function (preload recruitable stroke work relationship; ergs x 10(3)/mL) was significantly (p < 0.001) better for WB (WB, 80 +/- 11; CB, 67 +/- 13; CC, 57 +/- 12). Systolic function (maximum elastance relationship; mm Hg/mL) was also significantly (p < 0.001) better for WB (WB, 11.6 +/- 3.6; CB, 8.6 +/- 2.7; CC, 6.2 +/- 1.3). Diastolic function (stress-strain relationship; dynes x 10(3)/cm2) revealed significantly (p < 0.001) decreased compliance for CC (WB, 20 +/- 6; CB, 19 +/- 7; CC, 27 +/- 11). Left anterior descending coronary artery regional adenosine triphosphate/adenosine diphosphate ratios were significantly (p = 0.02) worse for CC (WB, 10.2 +/- 2.3; CB, 9.4 +/- 2.6; CC, 5.6 +/- 1.5). Myocardial edema significantly (p = 0.03) increased over time only in the CC animals (WB, 0.4% +/- 2.3%; CB, -0.3% +/- 3.6%; CC, 5.5% +/- 2.3%). In this model of acute regional myocardial ischemia and revascularization, continuous retrograde warm aerobic blood cardioplegia provided superior myocardial protection compared with cold oxygenated crystalloid cardioplegia with intermediate results for cold blood cardioplegia.

Surgical myocardial revascularization after acute infarction

The records of 288 patients undergoing isolated surgical myocardial revascularization between June 1989 and September 1992 were reviewed to determine the relative risk associated with surgery after an acute myocardial infarction (MI). A total of 73 patients (25 percent) were operated on within 30 days of an acute infarction while 215 patients (75 percent) had no history of recent infarction. Patients with an acute infarction were more likely to have regional wall motion abnormalities on ventriculography (mean wall score 6.7 vs 4.9, p = 0.001), require preoperative balloon pumping (15.1 percent vs 5.6 percent, p = 0.01), and have recent symptoms of congestive heart failure (23 percent vs 12 percent, p = 0.02). Patients with an acute MI also had higher NYHA functional classification and greater urgency of surgery. Despite these differences, overall mortality was lower in the acute MI group than in the control population (1.4 percent vs 2.3 percent, p = 0.623). Weaning from bypass was not appreciably more difficult in patients with an acute MI, nor were there differences in the mean number of hours of balloon pump or inotrope support.

Warm blood cardioplegia: superior protection after acute myocardial ischemia

Three myocardial protection techniques were studied in a canine model of acute myocardial ischemia with subsequent revascularization. Eighteen animals were randomly assigned to one of three treatment regimens: cold oxygenated crystalloid cardioplegia (CC), cold blood cardioplegia with modified reperfusate (CB), and continuous aerobic warm blood cardioplegia (WB) (n = 6 per group). Systemic hypothermic cardiopulmonary bypass (28 degrees C), antegrade arrest, and intermittent retrograde and antegrade delivery were used for the CC and CB groups. Systemic normothermic cardiopulmonary bypass, antegrade arrest, and continuous retrograde delivery were used for the WB group. Fifteen minutes of warm global ischemia was followed by occlusion of the left anterior descending coronary artery (15-minute duration) and simultaneous initiation of cardioplegic arrest (60-minute duration) to simulate clinical revascularization. After reperfusion, the animals were separated from cardiopulmonary bypass. Myocardial function, electrocardiogram, myocardial energetics, water content, histopathology, and defibrillation requirements were compared between groups. There was no significant difference in maximum elastance, myocardial oxygen consumption, myocardial edema, or histopathologic evidence of injury between groups. However, overall ventricular function, assessed by the slope of the preload recruitable stroke work relationship, was significantly better for the WB group (p = 0.04) (WB, 73 +/- 9; CB, 56 +/- 7; CC, 47 +/- 5). Diastolic function as assessed by the slope of the stress-strain relationship was significantly worse overall for the cold groups (p = 0.001) (WB, 20 +/- 2.2; CB, 39 +/- 1.3; CC, 37 +/- 3.1). Myocardial injury as assessed by ST segment elevation (millimeters) was less for the WB group (p = 0.03) (WB, 0.4 +/- 0.3; CB, 1.7 +/- 0.2; CC, 1.6 +/- 0.7). Countershocks necessary to restore sinus rhythm after cross-clamp removal were fewer in the WB group (p = 0.03) (WB, 0.8 +/- 0.3; CB, 4.0 +/- 1.2; CC, 5.5 +/- 1.5). In this model of acute global myocardial ischemia, continuous aerobic warm blood cardioplegia has important advantages over two widely used clinical hypothermic protection techniques.

Cold and warm blood cardioplegia

The present review concerns modern operative myocardial management strategies utilizing cold and warm blood cardioplegia. Both biological and surgical rationales toward providing optimal operative conditions in which to conduct complicated procedures are discussed. An alternative technique employing both cold and warm blood cardioplegia, as well as a cardioplegic formulary are proposed.