Technique and pitfalls of retrograde continuous warm blood cardioplegia

How to Protect Hypertrophied Myocardium? A Prospective Clinical Trial of three Preservation Techniques

Protection of the hypertrophied myocardium during heart surgery is still a controversial matter. We prospectively studied 3 currently available preservation techniques in 60 patients operated on for isolated aortic stenosis. Patients were randomly assigned to one of the following groups:

CWB: continuous warm blood cardioplegia

ICB: intermittent cold blood with warm blood controlled reperfusion

Cryst: intermittent cold crystalloid cardioplegia (SLF11, Biosédra Laboratory, Vernon, France).

All groups were matched for age, ejection fraction, NYHA class, aortic valve surface, and operative risk score. There were no deaths. No statistically significant difference was found among the groups in terms of ventilatory support time, ICU stay time, hospitalization or atrial fibrillation occurrence. Blood gases in the coronary sinus at the time of clamp release showed deep acidosis with crystalloid cardioplegia (pH = 7.11 vs 7.39 for CWB and 7.38 for UCB, p < 0.0001) associated with a higher lactate production than in the other groups (1.3 mmol vs 0.5 for CWB and 0.58 for ICB, p < 0.0001). Acidosis was corrected at the end of bypass with no significant differences among groups. CK-MB samples were taken on arrival in ICU, then 6 and 24 hours later. These samples showed much higher levels with cold blood (H6: 70 mcg/l vs 33 for CWB and 45 for Cryst, p = 0.0019). Although the 3 types of cardioplegia may be safely used for isolated aortic stenosis surgery, continuous warm blood cardioplegia appears to be the best choice.

Beating heart continuous coronary perfusion for valve surgery: what next for clinical trials?

Prior to the introduction of cardioplegia, beating heart continuous coronary perfusion (BHCCP) was the only available method of myocardial protection. Currently, cardiac surgery on cardiopulmonary bypass with cardioplegic arrest is the gold standard strategy. Cardioplegic arrest provides an easier and safer way to operate on a still heart. It enables the performance of a broader range of cardiac procedures, and avoids the potential difficulties of continuous perfusion on a beating heart. Despite the overall effectiveness and safety of cardioplegia, some adverse effects remain, mainly due to the insult of ischemia, which results in ischemic reperfusion injury. As a result BHCCP has seen a revival as an alternative to cardioplegia for performing complex valvular surgery. Increasing experience reporting safety and efficacy of BHCCP is being published. However, despite the reported advantages, current available evidence validating safety and efficacy of BHCCP is controversial. This article provides an overview of BHCCP highlighting the current best available evidence supporting this strategy, concerns, controversies and potential areas for further research.

Assessment of the position of retrograde cardioplegia catheter: comparison of hemodynamic versus manual evaluation in a prospective randomized trial

OBJECTIVE

To evaluate a hemodynamic method for the assessment of the position of the retrograde cardioplegia catheter (RCC) versus conventional Manual Assessment.

METHODS

We randomized 200 patients undergoing aortic valve surgery to Manual (n = 101) or Hemodynamic Assessment (n = 99). In the Hemodynamic group a 25% pressure increase at the tip of the RCC when a fistula with the ascending aorta was created via a luer-lock was considered indicative of correct RCC placement. Transesophageal echocardiography was used as a comparison evaluation method.

RESULTS

The Hemodynamic and Manual Assessment considered the RCC positioning successful in 89.9% versus 85.1% of cases. Echocardiography confirmed these results in Hemodynamic group but revealed 23 cases of misrecognized incorrect placement in the Manual group (p < 0.0001). Manual maneuvers resulted in 18 cases of secondary displacement and 19 cases of hemodynamic instability (p < 0.0001).

CONCLUSIONS

The Hemodynamic Method is quantitative, reproducible, highly reliable, and safer than palpation in the posterior atrioventricular groove.

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.

Does normothermic normokalemic simultaneous antegrade/retrograde perfusion improve myocardial oxygenation and energy metabolism for hypertrophied hearts?

BACKGROUND

Beating-heart valve surgery appears to be a promising technique for protection of hypertrophied hearts. Normothermic normokalemic simultaneous antegrade/retrograde perfusion (NNSP) may improve myocardial perfusion. However, its effects on myocardial oxygenation and energy metabolism remain unclear. The present study was to determine whether NNSP improved myocardial oxygenation and energy metabolism of hypertrophied hearts relative to normothermic normokalemic antegrade perfusion (NNAP).

METHODS

Twelve hypertrophied pig hearts underwent a protocol consisting of three 20-minute perfusion episodes (10 minutes NNAP and 10 minutes NNSP in a random order) with each conducted at a different blood flow in the left anterior descending coronary artery (LAD [100%, 50%, and 20% of its initial control]). Myocardial oxygenation was assessed using near-infrared spectroscopic imaging. Myocardial energy metabolism was monitored using localized phosphorus-31 magnetic resonance spectroscopy.

RESULTS

With 100% LAD flow, both NNAP and NNSP maintained myocardial oxygenation, adenosine triphosphate, phosphocreatine, and inorganic phosphate at normal levels. When LAD flow was reduced to 50% of its control level, NNSP resulted in a small but significant decrease in myocardial oxygenation and phosphocreatine, whereas those measurements did not change significantly during NNAP. With LAD flow further reduced to 20% of its control level, both NNAP and NNSP caused a substantial decrease in myocardial oxygenation, adenosine triphosphate, and phosphocreatine with an increase in inorganic phosphate. However, the changes were significantly greater during NNSP than during NNAP.

CONCLUSIONS

Normothermic normokalemic simultaneous antegrade/retrograde perfusion did not improve, but slightly impaired myocardial oxygenation and energy metabolism of beating hypertrophied hearts relative to NNAP. Therefore, NNSP for protection of beating hypertrophied hearts during valve surgery should be used with extra caution.

Management of catheter-related injuries to the coronary sinus

BACKGROUND

Although coronary sinus catheter-related injuries (CSCRIs) are rare, they are potentially lethal. The purpose of this study was to evaluate such injuries, the repair methods used, and to identify related risk factors for mortality.

METHODS

A retrospective review of 10,552 cardiac surgical procedures from 1995 to 2000 in which retrograde cardioplegia was used revealed 10 cases (n = 10) of CSCRIs (0.095%) at our center. These injuries occurred during coronary bypass, valve replacement, and combined procedures. Management included direct suture, vein patch, or pericardial "on-lay" patch repair.

RESULTS

Two deaths occurred (20% mortality) from failure of CSCRI repair; 8 of 10 injuries (80%) were successfully repaired. One patient had delayed, localized pericardial tamponade, which resolved spontaneously. Two patients had recurrent angina that was assessed 3 and 5 years later by coronary angiography; the coronary sinus was found to be patent in both cases. The remaining 6 patients have been asymptomatic.

CONCLUSIONS

Repair of CSCRIs can be challenging as it can be complicated by inadequate myocardial protection, inadvertent coronary artery injuries, and possibly, subsequent coronary sinus thrombosis. Repair of CSCRIs should be carried out on an arrested, well-protected heart providing secure hemostasis and coronary sinus patency.

Retrograde cardioplegia

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

The effects of retrograde cardioplegia technique on myocardial perfusion and energy metabolism: a magnetic resonance imaging and localized phosphorus 31 spectroscopy study in isolated pig hearts

OBJECTIVE

The present work was designed to study the myocardial perfusion and energy metabolism during retrograde cardioplegia performed with different methods, including deep coronary sinus cardioplegia, coronary sinus orifice cardioplegia, and right atrial cardioplegia.

METHODS

Isolated pig hearts were subjected to antegrade cardioplegia, right atrial cardioplegia, deep coronary sinus cardioplegia, and coronary sinus orifice cardioplegia in a random order. Cardioplegic distribution was assessed by T1-weighted magnetic resonance imaging in 1 group of hearts (n = 8). The flow dynamics of cardioplegia were assessed by T2*-weighted imaging in a second group of hearts (n = 8).

RESULTS

T1-weighted images revealed an apparent perfusion defect in the posterior wall of the left ventricle, the posterior portion of the interventricular septum, and the right ventricular free wall during deep coronary sinus cardioplegia. The perfusion defect observed in the first 2 regions with deep coronary sinus cardioplegia resolved with coronary sinus orifice cardioplegia. Right atrial cardioplegia provided the most homogeneous perfusion to all regions of the myocardium relative to the other 2 retrograde cardioplegia modalities. T2*-weighted images showed that the 3 retrograde cardioplegia modalities provided similar cardioplegic flow velocities. Localized phosphorus 31 spectroscopy showed that the levels of adenosine triphosphate and phosphocreatine were significantly lower in the posterior wall (adenosine triphosphate, 42.86% +/- 5.91% of its initial value; phosphocreatine, 11.43% +/- 11.3%) than the anterior wall (adenosine triphosphate, 89.19% +/- 8.83%; phosphocreatine, 59.54% +/- 12.58%) of the left ventricle during 70 minutes of normothermic deep coronary sinus cardioplegia.

CONCLUSIONS

Deep coronary sinus cardioplegia results in myocardial ischemia in the posterior wall of the left ventricle and the posterior portion of the interventricular septum, as well as in the right ventricular free wall. Coronary sinus orifice cardioplegia improves cardioplegic distribution in these regions. Relative to deep coronary sinus cardioplegia and coronary sinus orifice cardioplegia, right atrial cardioplegia provides the most homogeneous perfusion.

Effects of retrograde cardioplegia on myocardial perfusion and energy metabolism in immature porcine myocardium

OBJECTIVES

Retrograde cardioplegia has been widely used for the protection of adult hearts during cardiac operations. Its efficacy to protect immature myocardium is still unclear. This study was designed to assess the effects of retrograde cardioplegia on myocardial perfusion and energy metabolism in immature hearts.

METHODS

Piglet hearts were divided into 3 groups. Hearts in group 1 were used to assess myocardial perfusion of retrograde cardioplegia by means of magnetic resonance imaging. Hearts in groups 2 and 3 were used to assess the effects of retrograde cardioplegia on myocardial energy metabolism by use of phosphorus 31 magnetic resonance spectroscopy.

RESULTS

Magnetic resonance images showed that perfusion with retrograde cardioplegic solution was heterogeneous. A perfusion defect was noted during retrograde cardioplegia in the right ventricular wall and in a portion of the posterior wall of the left ventricle in 4 of 6 hearts. Phosphorus 31 spectra showed that at the end of 45-minute retrograde cardioplegia, myocardial intracellular pH was 6.83 +/- 0.17 and phosphocreatine was 53.5% +/- 27% of its prearrest value. The adenosine triphosphate level, however, remained normal throughout the retrograde cardioplegia period. Last, the hearts subjected to retrograde cardioplegia or antegrade cardioplegia showed similar and complete metabolic and functional recovery during reperfusion.

CONCLUSIONS

Retrograde cardioplegia provides heterogeneous perfusion. Its ability to protect the right ventricular myocardium is poor and varies between individuals. Myocardial perfusion provided by retrograde cardioplegia is slightly less than that needed to sustain normal myocardial energy metabolism under normothermic conditions.

Perspectives on myocardial protection: warm heart surgery

Continuous normothermic blood cardioplegia (CNBC), was recently introduced into clinical cardiac surgery and has generated great interest. CNBC represents the evolution of concepts which were initially described in the 1950s but which were forgotten as hypothermia became the main ingredient in all cardioplegic techniques and in heart surgery in general. The historical background to the development of CNBC is presented, as well as a review of the current state of knowledge about normothermic heart surgery. The limitations and pitfalls of the method are highlighted, along with future developments and perspectives.

Clamp for coronary artery operations

Aortocoronary bypass grafting is an accepted procedure for ischemic heart disease. Proper visualization of the coronary artery is mandatory for good surgical anastomosis. This is essential when a coronary operation is performed without cardioplegia or in surgical procedures without bypass support. For better visualization of a coronary artery, we are presenting a coronary artery clamp. We have used this clamp in minimally invasive coronary artery operations to achieve a bloodless field.

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.

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.

Is warm retrograde blood cardioplegia better than cold for myocardial protection?

BACKGROUND

This study tests the hypothesis that continuous normothermic retrograde blood cardioplegia is superior to cold intermittent blood cardioplegia in protecting the left and right side of the heart transmurally during an extended cross-clamping period.

METHODS

Twelve anesthetized, open chest dogs were placed on cardiopulmonary bypass and randomized to receive continuous warm (n = 6) or intermittent cold cardioprotection (n = 6) during a 3-hour aortic cross-clamp period. Transmural left ventricular muscle biopsy specimens were taken before the initiation of cardiopulmonary bypass and 90 and 180 minutes after cross-clamping. Right ventricular (RV) biopsy specimens were taken 180 minutes after aortic cross-clamping. Biopsy specimens were analyzed for adenosine triphosphate, creatine phosphate, and lactate levels and for morphologic changes via electron microscopy.

RESULTS

At the end of 180 minutes of cardiopulmonary bypass, the adenosine triphosphate contents of endocardial and epicardial halves of the left ventricular myocardium were only slightly degraded in both cardioplegia groups; a significantly greater reduction in adenosine triphosphate levels occurred in the RV of the warm compared with the cold group (p < 0.02). The difference in creatine phosphate values in the left ventricle between the cold group (35.2 +/- 23.4 nmol/mg cardiac protein) and the warm animals (64.4 +/- 24.9 nmol/mg cardiac protein) was not statistically significant, but the RV creatine phosphate stores were significantly better preserved in the warm compared with the cold cardioplegia group (p < 0.02). Lactate levels increased to a similar extent in both groups, but both values rose significantly over baseline (p < 0.03). Importantly the electron microscopic score of the left ventricle and RV indicated that cells were reversibly and not irreversibly damaged with both cardioplegic protections.

CONCLUSIONS

These results suggest the following: (1) Chemical arrest is a major contributor of myocardial preservation during diastolic arrest as used in clinical cardiac surgery. (2) Both methods preserve the ultrastructure of the myocytes transmurally during 3 hours of aortic cross-clamping. (3) Both techniques protect the RV and left ventricle; however, to provide optimal protection of the RV, alternated retrograde and antegrade perfusion might be beneficial over retrograde cardioplegia flow alone, in particular with warm cardioplegia.

Glucose level and myocardial recovery after warm arrest

BACKGROUND

During induced cold ischemia for cardiac operations, increasing glucose concentration is not thought to enhance myocardial protection and may detrimentally affect recovery. However, during "warm aerobic" arrest, increased glucose availability as substrate could enhance postischemic metabolic and functional recovery, as during and after ischemia, myocytes shift preference for substrate from fatty acids to glucose. Unfortunately, hyperglycemia may also increase patient susceptibility to neurologic injury.

METHODS

This experiment was designed to study the optimal dose of glucose and its effect on function during warm arrest. Isolated, retrograde-perfused rabbit hearts received multidose cardioplegia containing increasing concentrations of glucose, from 0 to 88 mmol/L, and underwent 120 minutes of "warm" 34 degrees C global ischemia. Osmolarities were adjusted equivalently.

RESULTS

After 34 degrees C ischemia, hearts treated with 5 to 88 mmol/L glucose showed significantly better functional recovery than those treated with 0 to 1 mmol/L glucose. However, the addition of 22 mmol/L glucose demonstrated optimal recovery with no further incremental enhancement with more glucose. Additional hearts receiving 0 or 22 mmol/L glucose had high-energy phosphates, lactate, CO2, and pH measured. The 22 mmol/L glucose hearts demonstrated active metabolism and significantly better recovery of high-energy phosphate levels than controls.

CONCLUSIONS

Increasing glucose level modestly during warm arrest enhanced recovery, but profound hyperglycemia did not incrementally improve this effect, mandating a cautious use of glucose.

Effect of the potassium-channel opener nicorandil as an adjunct to cardioplegia on myocardial preservation in isolated rabbit hearts

We studied the effect of nicorandil on the hemodynamic, biochemical, and ultrastructural changes in rabbit hearts (n = 50) rendered cardioplegic with a single injection of Bretschneider's HTK solution over 30 min or 60 min at 37 degrees C or 15 degrees C, followed by reperfusion at 37 degrees C for 60 min. Particular attention was focused on the aspects of dose-response relationship, temperature sensitivity, and ischemic tolerance. Isolated hearts were prepared for modified Langendorff circulation using modified Krebs-Henseleit bicarbonate solution bubbled with a 95% O2(-5)% CO2 gas mixture, to which nicorandil (0, 0.1, 1, and 5 mM) was added. The optimal concentration of nicorandil was 1mM, which increased the recovery of left ventricular (LV) function, affecting coronary flow and the myocardial cyclic adenosine monophosphate, but not the myocardial concentrations of adenine nucleotide compounds or total calcium. These effects were abolished by the addition of glibenclamide to the HTK, but they were not diminished by a high potassium (K+) concentration of 20mM. The addition of nicorandil 1mM to the HTK at 15 degrees C did not improve the recovery of LV function. Our result suggested that nicorandil used adjunctly prevents LV functional depression after 30min, and possibly 60min of cardioplegia at 37 degrees C, and that this effect is not disturbed by a high K+ concentration up to 20 mM. However, nicorandil has temperature sensitivity whereby it loses its efficacy at 15 degrees C.

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.

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.

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)

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)

Hemodynamic significance of the coronary vein valves

The incidence and morphology of one-way coronary vein valves were studied, together with their influence on the administration of retrograde cardioplegia. Calf, juvenile pig, and adult mongrel canine hearts (12 each) and human cadaver hearts (five adult and seven pediatric) were dissected. The pressure gradients between the coronary sinus and the posterior vein of the left ventricle were measured in 21 hearts during the retrograde administration of fluid. Species differences were noted, with apparently competent valves seen more frequently in calf hearts (mean, 1.33 valves +/- 0.22 [SEM] per heart) than in pig hearts (mean, 0.83 +/- 0.17 [SEM] per heart). In humans, more valves were seen in pediatric hearts (five valves in seven hearts) than in adult hearts (one valve in five hearts). No competent valves were found in dog hearts (chi 2 analysis; p < 0.0001). In calf hearts, a pressure gradient of 5 to 35.5 mm Hg was required before the valve opened. In pig hearts, these opening pressure gradients ranged from 0 to 19.5 mm Hg. The distribution of retrograde cardioplegia may be impaired in the presence of competent valves, particularly when low coronary sinus pressures are used.

Prospective, randomized trial of retrograde warm blood cardioplegia: myocardial benefit and neurologic threat

From March 1991 through July 1992, 1,001 patients having elective coronary artery bypass grafting were randomized to receive either continuous warm (> or = 35 degrees C) blood cardioplegia with systemic normothermia (> or = 35 degrees C) or intermittent cold (< or = 8 degrees C) oxygenated crystalloid cardioplegia and moderate systemic hypothermia (< or = 28 degrees C). Preoperative variables including age, sex, prior coronary bypass grafting, hypertension, prior myocardial infarction, diabetes, angina class, and preoperative heart failure class were similar in both groups, as were the intraoperative variables of number of coronary grafts, mammary artery use, and cardiopulmonary bypass time. Aortic cross-clamp time was significantly longer in the warm group (46 +/- 23 minutes versus 40 +/- 21 minutes). Most postoperative variables including mortality (warm, 1.0%, and cold, 1.6%), Q wave infarction (warm, 1.4%, and cold, 0.8%), and need of an intraaortic balloon pump (warm, 1.4%, and cold, 2.0%) were similar between groups. Total neurologic events (warm, 4.5%, and cold, 1.4%; p < 0.005) and perioperative strokes (warm, 3.1%, and cold, 1.0%; p < or = 0.02) were significantly higher in the warm group. Neurologic events included perioperative stroke (warm, 15 patients, and cold, 5 patients; p < 0.02), perioperative encephalopathy (warm, 2 patients, and cold, 1 patient), and delayed (> or = 3 in-hospital days) stroke (warm, 5 patients, and cold, 1 patient). All patients experiencing a stroke had a persistent neurologic deficit at the time of discharge. Encephalopathy resolved completely in all instances.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Retrograde cardioplegia: when and how. A review

With the introduction of balloon catheters enabling blind transatrial cannulation of the coronary sinus, retrograde cardioplegia is gaining increasing popularity. In several situations retrograde cardioplegia offers distinct technical advantages. Although not yet clinically documented, some patient subgroups with severe coronary stenoses/occlusion may probably benefit from retrograde cardioplegia. This technique is a valuable addendum to the technical repertoire of cardiac surgeons.

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.

Coronary sinus injuries during retrograde continuous normothermic blood cardioplegia

Injuries to the coronary sinus during cardioplegic arrest are rare but potentially lethal. We herein present case reports of injuries to the coronary sinus occurring during retrograde continuous normothermic blood cardioplegia, and emphasize preventive measures and treatment.

A randomized study of the systemic effects of warm heart surgery

The technique of warm heart surgery is defined as continuous warm blood cardioplegia and normothermic cardiopulmonary bypass. Although the systemic effects of traditional myocardial protection are well known, the effects of warm heart surgery are not. In a prospective trial, 204 patients undergoing coronary artery bypass grafting were randomized to the warm heart surgery technique (normothermic group) or traditional intermittent cold blood cardioplegia and cardiopulmonary bypass (hypothermic group). The groups had similar heparin sodium requirement, activated clotting times, urine output, hematocrit, and blood product utilization. There were no differences in hemodynamics immediately after cardiopulmonary bypass. The normothermic patients had a higher incidence of spontaneous defibrillation at cross-clamp removal (84%) than the hypothermic patients (33%) (p less than 0.01). An increase in the flow rate of low K+ cardioplegia was necessary to eradicate electrical activity during aortic occlusion more often in the normothermic patients (20%) than in the hypothermic patients (3%) (p less than 0.01). When low K+ cardioplegia was ineffective, high K+ cardioplegia was necessary to eradicate electrical activity in 31% of the normothermic patients compared with 10% of the hypothermic patients (p less than 0.05). The total cardioplegia volume delivered to the normothermic group (4.7 +/- 1.9 L) was higher than that delivered to the hypothermic group (2.6 +/- 0.8 L) (p less than 0.01). Although urine output was similar in both groups, the serum K+ levels were higher in the normothermic group (5.7 +/- 0.8 mmol/L) than in the hypothermic group (5.3 +/- 0.8 mmol/L) (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)