The cardioplegic solution HTK: effects on membrane potential, intracellular K+ and Na+ activities in sheep cardiac Purkinje fibres

Heart preservation in HTK solution: role of coronary vasculature in recovery of cardiac function

BACKGROUND

Poor myocardial tolerance to prolonged cold ischemia remains a major concern in heart transplantation. In this study, we estimated superiority of Histidine-Tryptophan-Ketoglutarate (HTK) over University of Wisconsin (UW) as a cardiac preservation solution.

METHODS

Isolated rat hearts were mounted on a Langendorff apparatus to estimate the baseline cardiac function. The hearts were arrested and stored at 4 degrees C in UW and HTK solution for 8 hours, and then reperfused. The aortic flow, coronary flow, cardiac output, rate pressure product, and left ventricular dp/dt in the HTK group recovered significantly more than the UW group. The values of myocardial total adenine nucleotides and the adenosine triphosphate to adenosine diphosphate ratio were higher in the HTK than in the UW group. We also examined coronary vascular responsiveness using left coronary arteries dissected from the rat hearts before flushing, before storage, after storage, and after reperfusion.

RESULTS

The maximal relaxation response to acetylcholine was significantly higher in the HTK than in the UW group after reperfusion, although there were no significant differences at each stage before reperfusion. In addition, the endothelium-independent relaxation response to sodium nitroprusside in the HTK group was also well preserved after reperfusion.

CONCLUSIONS

These results indicate that HTK is superior to UW solution for cardiac preservation. HTK protects coronary vasculature during preservation, which together with reperfusion might lead to improved functional cardiac recovery following preservation.

Comparison of polarized and depolarized arrest in the isolated rat heart for long-term preservation

BACKGROUND

Hypothermic hyperkalemic cardioplegic solutions are currently used for donor heart preservation. Hyperkalemia-induced depolarization of the resting membrane potential (Em) may predispose the heart to Na+ and Ca2+ loading via voltage-dependent "window currents," thereby exacerbating injury and limiting the safe storage duration. Alternatively, maintaining the resting Em with a polarizing solution may reduce ionic movements and improve postischemic recovery; we investigated this concept with the reversible sodium channel blocker tetrodotoxin (TTX) to determine (1) whether polarized arrest was more efficacious than depolarized arrest during hypothermic long-term myocardial preservation and (2) whether TTX induces and maintains polarized arrest.

METHODS AND RESULTS

The isolated crystalloid-perfused working rat heart preparation was used in this study. Preliminary studies determined an optimal TTX concentration of 22 micromol/L and an optimal storage temperature of 7.5 degrees C. To compare depolarized and polarized arrest, hearts were arrested with either Krebs-Henseleit (KH) buffer (control), KH buffer containing 16 mmol/L K+, or KH buffer containing 22 micromol/L TTX and then stored at 7.5 degrees C for 5 hours. Postischemic recovery of aortic flow was 13+/-4%, 38+/-2%, and 48+/-3%* (*P<.05 versus control and 16 mmol/L K+), respectively. When conventional 3 mol/L KCl-filled intracellular microelectrodes were used, Em gradually depolarized during control unprotected ischemia to approximately -55 mV before reperfusion, whereas arrest with 16 mmol/L K+ caused rapid depolarization to approximately -50 mV, where it remained throughout the 5-hour storage period. In contrast, in 22 micromol/L TTX-arrested hearts, Em remained more polarized, at approximately -70 mV, for the entire ischemic period.

CONCLUSIONS

Blockade of cardiac sodium channels by TTX during ischemia maintained polarized arrest, which was more protective than depolarized arrest, possibly because of reduced ionic imbalance.

Prolonged hypothermic cardiac storage with histidine-tryptophan-ketoglutarate solution: comparison with glucose-insulin-potassium and University of Wisconsin solutions

BACKGROUND

The purpose of this study was to compare the efficacy of histidine-tryptophan-ketoglutarate (HTK) solution after prolonged cold storage with that of the conventional glucose-insulin-potassium (GIK) and University of Wisconsin (UW) solutions in experimental heart preservation. GIK solution was chosen as a control to mimic current clinical regimens. Variables of cardiac function, myocardial tissue water, and adenine nucleotide pool metabolites were used to assess prolonged myocardial preservation in the isolated rat heart model.

METHODS

Hearts isolated from male Wistar rats were mounted on a Langendorff apparatus to estimate baseline cardiac function. The hearts were divided into three groups (n=6 per group) according to each preservation solution used: group 1, GIK solution; group 2, UW solution; and group 3, HTK solution. The hearts were then arrested and stored in each solution for 6, 8, and 12 hr at 4 degrees C. After storage, the hearts were reperfused and recovery of cardiac function and myocardial tissue water content were evaluated. Myocardial adenylate contents just after storage in each group (n=5 hearts/group) were also measured.

RESULTS

The hearts stored in HTK solution showed maintenance of cardiac function at up to 8 hr of almost 80% of prepreservative baseline function; however, recovery of cardiac function of the hearts stored in UW solution revealed an initial loss of function at 6 hr of almost 60% and a decline to 50% at 8 hr. Furthermore, recovery of cardiac function of the hearts stored in GIK solution revealed a progressive loss of function at 6 hr of storage of almost 50% and a decline to 30% at 8 hr of storage. The myocardial ATP/ADP ratios after 6 hr of storage in HTK and UW solutions were significantly higher than the ratio found in GIK solution. Although the myocardial ATP/ADP ratio after 8 hr of storage in HTK solution was maintained above 50%, the ratios in GIK and UW solutions declined to 15%. In addition, the myocardial energy charge values of the hearts stored in HTK solution were sufficiently maintained until 8 hr of storage, whereas the values in UW and GIK solutions declined to below 50% at 6 hr of storage and 20% at 8 hr of storage. Although there were no significant differences in tissue water contents after 6 and 8 hr of storage among the three groups, the water contents of the hearts after 12 hr of storage in HTK and UW solutions were significantly lower than that of the hearts stored in GIK solution.

CONCLUSIONS

Our results suggest that HTK solution is much more effective than UW and GIK solutions for isolated rat heart preservation; however, successful cold storage of the heart is highly energy-dependent, and a dramatic breakdown of myocardial energy level, which causes a crucial decline in cardiac function, occurs between 8 and 12 hr of storage.

Sodium alterations in isolated rat heart during cardioplegic arrest

Triple-quantum-filtered (TQF) Na nuclear magnetic resonance (NMR) without chemical shift reagent is used to investigate Na derangement in isolated crystalloid perfused rat hearts during St. Thomas cardioplegic (CP) arrest. The extracellular Na contribution to the NMR TQF signal of a rat heart is found to be 73 +/- 5%, as determined by wash-out experiments at different moments of ischemia and reperfusion. With the use of this contribution factor, the estimated intracellular Na ([Na+]i) TQF signal is 222 +/- 13% of preischemic level after 40 min of CP arrest and 30 min of reperfusion, and the heart rate pressure product recovery is 71 +/- 8%. These parameters are significantly better than for stop-flow ischemia: 340 +/- 20% and 6 +/- 3%, respectively. At 37 degrees C, the initial delay of 15 min in [Na+]i growth occurs during CP arrest along with reduced growth later (approximately 4.0%/min) in comparison with stop-flow ischemia (approximately 6.7%/min). The hypothermia (21 degrees C, 40 min) for the stop-flow ischemia and CP dramatically decreases the [Na+]i gain with the highest heart recovery for CP (approximately 100%). These studies confirm the enhanced sensitivity of TQF NMR to [Na+]i and demonstrate the potential of NMR without chemical shift reagent to monitor [Na+]i derangements.

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.

Cardioprotective effect of nicorandil in histidine-tryptophan-ketoglurate solution during the cold storage of isolated hearts

We compared the efficacy of using histidine-tryptophan-ketoglurate (HTK) solution with that of University of Wisconsin (UW) solution for heart preservation in an isolated rat heart preparation. Nicorandil (NCR) exerts its action as an ATP-sensitive potassium channel opener at low extracellular potassium concentrations, and HTK solution has a low potassium concentration. Therefore, we also investigated the efficacy of using HTK solution with NCR following 12-hr preservation. Hearts isolated from male Wistar rats were mounted on a Langendorff apparatus to estimate baseline aortic flow (AF), coronary flow (CF), cardiac out-put (CO), heart rate (HR), systolic pressure (SP), aortic mean pressure, and the rate-pressure product (RPP). The hearts were divided into four groups: group 1, 8-hr storage in UW solution; groups 2 and 3, 8- or 12-hr storage in HTK solution, respectively; and group 4, 12-hr storage in HTK solution with NCR. They were arrested and stored at 4 degrees C in each preservation solution. Following storage, they were reperfused and postpreservative function was measured to assess cardiac functional recovery. Concentrations of creatine phosphokinase, troponin-T, and lactate in the coronary perfusate were measured. Frozen tissue samples from groups 3 and 4 were analyzed for adenylate content and cGMP. The myocardial water content was also measured. The recovery of AF, CF, CO, SP, and RPP in group 2 was significantly improved compared with that in group 1 (P<0.05). The recovery of AF, CF, CO and HR in group 4 was significantly better than that in group 3 (P<0.05). Creatine phosphokinase leakage in group 2 and troponin-T leakage in group 4 were significantly reduced (P<0.05 vs. groups 1 and 3, respectively). Total adenine nucleotides and the adenylate energy charge in group 4 were well sustained (P<0.05 vs. group 3). These results suggest that HTK solution is more effective than UW solution for cardiac preservation, and that NCR provides still better protection.

The contraction state of myofibrils during global ischemia and after reperfusion following different forms of cardiac arrest. Correlation with metabolic parameters in the canine heart

This study was undertaken in order to obtain information on the mode of reaction of the contractile apparatus after different forms of cardiac arrest, global ischemia and reperfusion, as well as on possible correlations between the contraction state of myofibrils and biochemical parameters. During the survival time, before the level of 3 mumol/gww creatine phosphate (CP) is reached, the contraction state shows only minor changes. During the revival time in which ATP tissue concentrations decay to 4 mumol/gww, the contribution of ATP, lactate, anorganic phosphate (Pa) and acidosis to the degree of relaxation depends on the method of cardiac arrest. At defined biochemical values, the degree of relaxation is comparable after aortic cross clamping (ACC) and St. Thomas perfusion, but significantly different compared to HTK perfusion. Thus, during the revival time, the relaxation of sarcomeres depends predominantly on the composition of the solutions used for cardiac arrest. The re-entry of contraction below 3 mumol/gww ATP is correlated with the ATP concentration, independent of the form of cardiac arrest. Reperfusion after HTK or St. Thomas cardioplegia and reversible ischemia leads to the focal formation of contraction bands, which do not occur during ischemia. This contraction state is significantly more pronounced after reperfusion of St. Thomas arrested hearts. Thus, the contraction state of myofibrils is influenced not only by alterations in metabolite concentrations, but also by the composition of cardioplegic solutions and by the characteristic conditions (sufficient energy, oxygen and Calcium) during reperfusion.

Extended cardiopulmonary preservation: University of Wisconsin solution versus Bretschneider's cardioplegic solution

Application of the University of Wisconsin cold storage solution has rapidly expanded to include medium-term to long-term preservation of virtually all intraabdominal organs. Its use in intrathoracic organ transplantation has also been suggested. We therefore examined the efficacy of the University of Wisconsin solution in a primate allotransplantation model for preservation of hearts, and as a simple single-solution system for static preservation of heart-lung blocks, for periods of ischemia ranging from 6 to 24 hours. For comparison, we employed the histidine-tryptophane-ketoglutarate cardioplegic solution of Bretschneider. University of Wisconsin solution provided superior results with regard to clinical outcome and hemodynamic recovery of hearts after ischemic periods of up to 16 hours. This was in contrast to Bretschneider's solution, which allowed storage of hearts for periods of only up to 10 hours. Heart-lung blocks were equally well preserved with either University of Wisconsin or Bretschneider's solution after 6 to 12 hours, although the University of Wisconsin solution group exhibited a more notable increase in pulmonary water content. This was in accordance with histological data, which suggested that, although hemodynamic recovery of hearts stored for periods longer than 10 hours was poor, preservation of pulmonary ultrastructure was far superior using Bretschneider's solution as compared with University of Wisconsin solution after an ischemic period of up to 16 hours.