Beta-blockade as an alternative to cardioplegic arrest during cardiopulmonary bypass

Hyperkalemic cardioplegia for adult and pediatric surgery: end of an era?

Despite surgical proficiency and innovation driving low mortality rates in cardiac surgery, the disease severity, comorbidity rate, and operative procedural difficulty have increased. Today's cardiac surgery patient is older, has a "sicker" heart and often presents with multiple comorbidities; a scenario that was relatively rare 20 years ago. The global challenge has been to find new ways to make surgery safer for the patient and more predictable for the surgeon. A confounding factor that may influence clinical outcome is high K(+) cardioplegia. For over 40 years, potassium depolarization has been linked to transmembrane ionic imbalances, arrhythmias and conduction disturbances, vasoconstriction, coronary spasm, contractile stunning, and low output syndrome. Other than inducing rapid electrochemical arrest, high K(+) cardioplegia offers little or no inherent protection to adult or pediatric patients. This review provides a brief history of high K(+) cardioplegia, five areas of increasing concern with prolonged membrane K(+) depolarization, and the basic science and clinical data underpinning a new normokalemic, "polarizing" cardioplegia comprising adenosine and lidocaine (AL) with magnesium (Mg(2+)) (ALM™). We argue that improved cardioprotection, better outcomes, faster recoveries and lower healthcare costs are achievable and, despite the early predictions from the stent industry and cardiology, the "cath lab" may not be the place where the new wave of high-risk morbid patients are best served.

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.

Impact of Acute Myocardial Edema on Left Ventricular Function

Studies of the impact of myocardial edema on left ventricular (LV) systolic function show conflicting results. We sought to evaluate the impact of increased myocardial water content (MWC) on LV systolic and diastolic function. Anesthetized dogs (n = 12) were instrumented with myocardial ultrasonic crystals and an LV micromanometer. Systolic function was measured by preload recruitable stroke work (PRSW) and dP/dt(max). Diastolic function was measured by -dP/dt(max) and the isovolumic relaxation constant tau (t). Myocardial water content (MWC) was determined using microgravimetry. In six dogs (coronary sinus hypertension, CSH group) we produced myocardial edema by inflating a coronary sinus balloon for 2 h (30-40 mm Hg). In six other dogs (Plegisol, PLEG group) cardiopulmonary bypass (CPB) was initiated (12.3 +/- 0.8 min), the aorta was cross-clamped (117 +/- 19 s), and 700 mL 4 degrees C crystalloid, hyperkalemic cardioplegic solution (Plegisol) was administered into the aortic root (62 +/- 4 mm Hg). After declamping and reperfusion (7.2 +/- 1.0 min), the dogs were separated from CPB. Myocardial function parameters and MWC were measured for 2 h after edema generation. In the CSH group, MWC significantly increased from 75.9 +/- 0.3% to 77.6 +/- 0.3% (p < .05). In the PLEG group, MWC increased from 75.8 +/- 0.3% to 77.7 +/- 0.3% (p < .05). PRSW and dP/dt(max) did not decrease in either group. Diastolic parameters did not change significantly. We conclude that acute myocardial edema without myocardial injury does not impair LV function.

Exsanguination cardiac arrest in rats treated by 60min, but not 75min, emergency preservation and delayed resuscitation is associated with intact outcome

Emergency preservation and resuscitation (EPR) is a new approach for resuscitation of exsanguination cardiac arrest (CA) victims to buy time for surgical hemostasis. EPR uses a cold aortic flush to induce deep hypothermic preservation, followed by resuscitation with cardiopulmonary bypass (CPB). We previously reported that 20 min of EPR was feasible with intact outcome. In this report, we tested the limits for EPR in rats. Adult male isoflurane-anesthetized rats were subjected to rapid hemorrhage (12.5 ml over 5 min), followed by esmolol/KCl-induced CA and 1 min of no-flow. EPR was then induced by perfusion with 270 ml of ice-cold Plasma-Lyte to decrease body temperature to 15 degrees C. After 60 min (n=7) or 75 min (n=7) of EPR, resuscitation was attempted with CPB over 60 min, blood transfusion, correction of acid-base balance and electrolyte disturbances, and mechanical ventilation for 2h. Survival, overall performance category (OPC: 1=normal, 5=death), neurological deficit score (NDS), and histological damage score (HDS) were assessed in survivors on day 3. While all rats after 60 min EPR survived, only two out of seven rats after 75 min EPR survived (p<0.05). All rats after 60 min EPR achieved OPC 1 and normal NDS by day 3. Survivors after 75 min EPR achieved best OPC 3 (p<0.05 vs. 60 min EPR). HDS of either brain or individual viscera was not statistically different after 60 versus 75 min EPR, except for kidneys (0+/-0 vs. 1.9+/-1.3, respectively; p<0.05), with a strong trend toward greater injury in all extracerebral organs in the 75-min EPR group (p<0.06). Histological findings were dominated by cardiac lesions observed in both groups and acute renal tubular and liver necrosis in the 75-min EPR group. In conclusion, we have shown that 60 min of EPR after exsanguination CA is associated with survival and favorable neurological outcome, while 75 min of EPR results in significant mortality and neurological damage in survivors. Surprisingly, extracerebral lesions predominated at 75-min EPR group. This model should serve as a screening model both for testing new pharmacological adjuncts to improve survival after exsanguination CA, and for elucidating the underlying mechanisms of ischemia/reperfusion injury.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Myocardial fluid balance

Fluid accumulation in the cardiac interstitium or myocardial edema is a common manifestation of many clinical states. Specifically, cardiac surgery includes various interventions and pathophysiological conditions that cause or worsen myocardial edema including cardiopulmonary bypass and cardioplegic arrest. Myocardial edema should be a concern for clinicians as it has been demonstrated to produce cardiac dysfunction. This article will briefly discuss the factors governing myocardial fluid balance and review the evidence of myocardial edema in various pathological conditions. In particular, myocardial microvascular, interstitial, and lymphatic interactions relevant to the field of cardiac surgery will be emphasized.

Regional dependence of cerebral reperfusion after circulatory arrest in rats

The severity of neurologic dysfunction after circulatory arrest depends on cerebral reperfusion during and after resuscitation. The objective of current study was to investigate the temporal and spatial patterns of the cerebral perfusion immediately after resuscitation. Precise control of circulatory arrest was achieved in rats by combination of asphyxia and transient blockage of cardiac-specific beta-adrenergic receptors with esmolol, an ultra-short-acting beta-blocker. Animals were randomized into 3 groups with resuscitation starting 0.5 (sham group, no asphyxia, n = 5), 4 (Group 2, n = 5), or 12 minutes (Group 3, n = 8) later by retrograde intraarterial infusion of donor blood along with a resuscitation mixture. Cerebral perfusion was measured by magnetic resonance imaging (MRI) using arterial spin labeling. The average perfusion before arrest was 163 +/- 27 mL 100 g(-1) min(-1) under isoflurane anesthesia. Resuscitation led to transient perfusion increase, which started from thalamus and hypothalamus and later shifted to the cortex. Severe hypoperfusion to as low as 6% to 20% of the normal level developed in the first 10 to 20 minutes of reperfusion and lasted for at least 2 hours. On the fifth day after circulatory arrest, all animals showed a normal level of perfusion (159 +/- 57 mL 100 g(-1) min(-1) ) and minimal neurologic deficit. Nevertheless, histologic examination revealed extensive changes in the CA1 region of the hippocampus consistent with global ischemia and reperfusion damage. The combination of an improved circulatory arrest model and noninvasive MRI cerebral perfusion measurements provides a powerful tool for investigations of circulatory arrest and resuscitation, allowing for evaluation of therapies aimed at modulating cerebral reperfusion.

Myocardial protection: the efficacy of an ultra-short-acting beta-blocker, esmolol, as a cardioplegic agent

OBJECTIVE

During myocardial revascularization, some surgeons (particularly in the United Kingdom) use intermittent crossclamping with fibrillation as an alternative to cardioplegia. We recently showed that intermittent crossclamping with fibrillation has an intrinsic protection equivalent to that of cardioplegia. In this study we hypothesized that arrest, rather than fibrillation, during intermittent crossclamping may be beneficial. Because esmolol, an ultra-short-acting beta-blocker, is known to attenuate myocardial ischemia-reperfusion injury, we compared the protective effect of esmolol arrest with that of intermittent crossclamping with fibrillation and conventional cardioplegia (St Thomas' Hospital solution).

METHODS

Isolated rat hearts were Langendorff perfused at either constant flow (14 mL/min) or constant pressure (75 mm Hg) with oxygenated Krebs-Henseleit bicarbonate buffer (37 degrees C), and left ventricular developed pressure was assessed. In study 1 (constant flow perfusion) 8 groups (n = 6 hearts per group) were studied: (1) 40 minutes of global ischemia; (2) 2 minutes of St Thomas' Hospital infusion and 40 minutes of ischemia; (3) multidose (every 10 minutes) infusions of St Thomas' Hospital solution during 40 minutes of ischemia; (4) 2 minutes of esmolol infusion and 40 minutes of ischemia; (5) multidose (every 10 minutes) esmolol infusions during 40 minutes of ischemia; (6) continuous infusion of esmolol for 40 minutes during coronary perfusion; (7) intermittent (4 x 10 minutes) ischemia with ventricular fibrillation; and (8) intermittent (4 x 10 minutes) ischemia preceded by intermittent esmolol administration. All protocols were followed by 60 minutes of reperfusion. Further experiments (study 2) examined the esmolol administration method in hearts perfused by constant pressure.

RESULTS

An optimal arresting dose of 1.0 mmol/L esmolol was established. In study 1 recovery of left ventricular developed pressure (expressed as percentage of preischemic value) was 7% +/- 4%, 28% +/- 8%, 70% +/- 5%, 8% +/- 1%, 90% +/- 4%, 65% +/- 3%, 71% +/- 5%, and 76% +/- 5% in groups 1 to 8, respectively. Intermittent esmolol arrest with global ischemia provided equivalent myocardial protection to intermittent crossclamping with fibrillation, continuous esmolol perfusion, and multidose St Thomas' Hospital solution. Surprisingly, multidose esmolol infusion was more protective than all other treatments. In further experiments (study 2) optimal recovery was obtained with multiple esmolol infusions (by constant flow or constant pressure), but continuous esmolol infusion (at constant flow) was less effective than constant pressure infusion.

CONCLUSIONS

Intermittent arrest with esmolol did not enhance protection of intermittent crossclamping with fibrillation; however, multiple esmolol infusions during global ischemia provided improved protection. Administration (constant flow or constant pressure) of arresting solutions influenced outcome only during continuous infusion. Multidose esmolol arrest may be a beneficial alternative to intermittent crossclamping with fibrillation or conventional cardioplegia.

Ultra-short-acting cardioselective beta-blockade attenuates postischemic cardiac dysfunction in the isolated rat heart

OBJECTIVES

We sought to test the effectiveness of ultra-short-acting cardioselective beta-blockade, landiolol hydrochloride, for warm heart surgery.

METHODS

The isolated perfused rat heart preparation was used. After preischemic measurement of cardiac function, 3 min of coronary infusion of crystalloid cardioplegic solution (37 degrees C) with landiolol hydrochloride of various concentrations (1, 2.5, 5, and 10 mmol/l) or without it (control group) was performed, followed by 30 min of warm ischemic arrest. Finally, postischemic function was measured.

RESULTS

The percentage recoveries of heart rate in hearts receiving 0, 1, 2.5, 5, and 10 mmol/l landiolol hydrochloride were 89.4+/-3.4%, 90.9+/-1.7%, 89.6+/-1.8%, 83.4+/-3.3%, and 74.3+/-1.9% (P<0.05 vs. 0, 1, and 2.5 mmol/l groups), respectively. The percentage recoveries of aortic flow were 55.6+/-3.1%, 62.8+/-3.3%, 75.0+/-4.2% (P<0.05 vs. 0 and 10 mmol/l groups), 65.3+/-5.3%, and 51.6+/-4.0%, respectively. Similar recovery profiles were observed with the first derivative of the rise in aortic pressure, stroke volume and stroke work. The total amount of coronary effluent in the hearts receiving 5 or 10 mmol/l was lower than in the other groups.

CONCLUSIONS

Landiolol hydrochloride has the potential to enhance postischemic cardiac function after the warm cardioplegic arrest. The optimal concentration for maximum postischemic functional recovery was 2.5 mmol/l, and recoveries of aortic flow and heart rate decreased in hearts receiving 5 mmol/l or more.