The role of cardioplegic solution buffering in myocardial protection

St. Thomas and del Nido cardioplegia are superior to Custodiol cardioplegia in a rat model of donor heart

OBJECTIVES

Cardiac transplantation is an effective treatment for advanced heart disease and protection of the donor organ is directly associated with post-transplantation outcomes. Cardioplegic strategies intend to protect the donor heart against ischemic injury during transplantation procedures. In our study, the effects of three different cardioplegia solutions were evaluated in a rat heart donor model in terms of cellular base. Design. Cardioplegia solutions as St. Thomas, del Nido or Custodiol were administered to male Wistar albino rats until cardiac arrest. Arrested hearts were excised and incubated in cold cardioplegia solutions for 4 h. Organ bath experiments were performed using the right ventricular free wall strips of the heart tissues. ATP, sialic acid, TNF-α levels and MMP-9 activities were measured in heart tissues. Incubation media were also used to measure TNF-α and troponin-I levels following organ baths experiments. Results. Custodiol administration led to reduced myocardial contraction (p < .05), decreased ATP levels (p < .001) and increased both TNF-α levels (p < .05), and MMP-9 activity (p < .05). Additionally, troponin-I and TNF-α levels in media were significantly increased (p < .05), TNF-α levels were positively correlated with MMP-9 activities (r = .93, p = .007) and negatively correlated with ATP levels (r = -.91, p = .01) in the Custodiol group. Also, MMP-9 activities were negatively correlated with ATP levels (r = -.90, p = .01) Conclusion. Custodiol cardioplegia cannot prevent functional and cellular damage in donor heart tissue. St. Thomas or del Nido cardioplegia could result in superior functional and biochemical improvement during transplantation procedures. In this respect, these cardioplegic solutions may be more advantageous as cellular and functional.

WITHDRAWN: Surgically induced myocardial ischemia: How best to mitigate the injury

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Comparing del Nido and Conventional Cardioplegia in Infants and Neonates in Congenital Heart Surgery

BACKGROUND

The aim of this study was to evaluate outcome measures after the use of del Nido (dN) cardioplegia compared with conventional multidose high-potassium (non-dN) cardioplegia in neonates and infants.

METHODS

We retrospectively analyzed data in patients, aged younger than 1 year, undergoing cardiopulmonary bypass (CPB) from January 2012 to August 2015. We changed our cardioplegia protocol from non-dN to dN administered in a single or infrequently dosed strategy in September 2013. The outcomes of the dN group (n = 107) are compared with the non-dN group (n = 118). We analyzed variables for demographic, intraoperative, early postoperative, and discharge variables.

RESULTS

The two groups were similar in age, weight, height, CPB, and cross-clamp time; preoperative and postoperative echocardiographic systolic functions; first 24-hour postoperative urine output and inotropic score; length of stay; and mortality rate. The Society of Thoracic Surgeons/European Association for Cardio-Thoracic Surgery Congenital Heart Surgery (STAT) mortality category was significantly higher in the dN group (p = 0.03). The cardioplegia dosing interval was lower for the non-dN group (p < 0.001). The volume and doses of cardioplegia per patient were significantly higher in the non-dN group (p < 0.001). In a subanalysis, when the Norwood patients were excluded from both groups, the overall STAT mortality category difference was no longer significant. The demographic, early postoperative, and discharge variables still showed no significant difference when the two groups were compared.

CONCLUSIONS

Similar outcomes can be achieved with less frequent interruption of the operation and lower volume of cardioplegia when using dN cardioplegia solution compared with conventional cardioplegia. The dN cardioplegia with extended ischemic interval can be used as an alternative strategy in the neonatal and infant population during cardiac operations.

Noteworthy Literature Published in 2016 for Cardiac Surgery

Cardiac surgical care of patients continued to evolve rapidly in 2016. In this article, 3 topics of considerable change are discussed based on recent publications. The first topic reviews the potential risks and benefits of newly instituted low-risk percutaneous aortic valve replacement. The second topic reviews the increasing utilization of more extensive arch replacements in acute type A dissection. The final topic reviews current trends and justification for changes in patterns of use of cardioplegia options. The topics discussed are contemporary issues facing cardiac surgery, so they should serve to address the reasoning for changes in contemporary practice in 2016.

Histidine-tryptophan-ketoglutarate solution decreases mortality and morbidity in high-risk patients with severe pulmonary arterial hypertension associated with complex congenital heart disease: an 11-year experience from a single institution

Cardioplegic reperfusion during a long term ischemic period interrupts cardiac surgery and also increases cellular edema due to repeated solution administration. We reviewed the clinical experiences on myocardial protection of a single perfusion with histidine-tryptophan-ketoglutarate (HTK) for high-risk patients with severe pulmonary arterial hypertension associated with complex congenital heart disease. This retrospective study included 101 high-risk patients undergoing arterial switch operation between March 2001 and July 2012. We divided the cohort into two groups: HTK group, myocardial protection was carried out with one single perfusion with HTK solution; and St group, myocardial protection with conventional St. Thomas' crystalloid cardioplegic solution. The duration of cardiopulmonary bypass did not differ between the two groups. The mortality, morbidity, ICU stay, post-operative hospitalization time, and number of transfusions in HTK group were lower than those in St group (P<0.05). Univariate and multivariate analysis showed that HTK is a statistically significant independent predictor of decreased early mortality and morbidity (P<0.05). In conclusion, HTK solution seems to be an effective and safe alternative to St. Thomas' solution for cardioplegic reperfusion in high-risk patients with complex congenital heart disease.

Feasibility and safety of continuous retrograde administration of Del Nido cardioplegia: a case series

Background

Del Nido (DN) cardioplegia, a calcium-free, hyperkalemic solution containing lidocaine and magnesium has been developed to help reduce intracellular calcium influx and the resulting myocyte damage in the immediate postischemic period following cardiac arrest. DN cardioplegia has been used for pediatric cardiac surgery but its use in complex reoperative surgery has not been studied. We specifically report the outcomes of patients undergoing reoperative cardiac surgery after previous coronary artery bypass grafting with a patent internal mammary artery (IMA).

Methods

Patients undergoing reoperative cardiac surgery with prior coronary bypass grafting surgery were studied between 2010 and 2013. Fourteen patients were identified who required continued retrograde cardioplegia administration. In all cases, an initial antegrade dose was given, followed by continuous retrograde administration. Demographics, co-morbidities, intra-operative variables including cardioplegia volumes, post-operative complications, and patient outcomes were collected.

Results

The mean age of all patients was 73.3+/−6.7 years, and 93 % were male. Aortic cross clamp time and cardiopulmonary bypass times were 81+/−35 and 151+/−79 mins, respectively. Antegrade, retrograde and total cardioplegia doses were 1101+/−398, 3096+/−3185 and 4367+/−3751 ml, respectively. An average of 0.93+/−0.92 inotropes and 1.50+/−0.76 pressors were used on ICU admission after surgery. ICU and total hospital lengths of stay were 5.5+/−7.4 and 9.6+/−8.0 days, respectively. Complications occurred in two patients (14 %) (pneumonia and prolonged mechanical ventilation) and new arrhythmias occurred in five patients (36 %) (four new-onset atrial fibrillation and one pulseless electrical activity requiring 2 min of chest compression). No perioperative myocardial infarctions were noted based on electrocardiograms and cardiac serum markers. Postoperatively, left ventricular function was preserved in all patients whereas two patients (14 %) had mild decrease in right ventricular function as assessed by echocardiography. No mortality was observed.

Conclusion

Del Nido cardioplegia solution provides acceptable myocardial protection for cardiac surgery that requires continuous retrograde cardioplegia administration. DN cardioplegia’s administration in a continuous retrograde fashion with a patent IMA is believed to provide adequate myocardial protection while avoiding injuring the IMA through dissection and clamping.

Evidence-based medicine and myocardial protection — where is the evidence?

Objective:

Myocardial protection with cardioplegia is an integral component of most cardiac surgical procedures, providing protection of the heart by limiting metabolic activity and increasing the myocardium’s capacity to withstand ischemia for prolonged periods of time. Cardioplegia has greatly affected the landscape of cardiothoracic surgery since its introduction in the 1960s, but, to this day, there continues to be a debate over what the ideal cardioplegic solution should be. The goal of this analysis is to describe current practices in cardioplegia and to point out the lack of quality human research and subsequent publications that prevent best practices from being utilized.

Methods:

This study is a systematic review of journal publications pertaining to the composition of commonly used cardioplegic solutions. Four main types of cardioplegia were assessed to give a narrower field of examination; specifically, microplegia, del Nido, Custodiol HTK, and 4:1 blood cardioplegia. Other combinations of cardioplegia, including St. Thomas’s Solution and the University of Wisconsin (UW) Solution, were considered when applicable according to the context of the publication being reviewed. Factors being assessed consisted of scientific validity, nature of the test subject (isolated organ vs. animal vs. human studies), experimental setup (retrospective trials vs. randomized clinical trials) and patient outcomes.

Results:

There are very few randomized clinical trials with human subjects comparing commonly used cardioplegic solutions. Numerous retrospective studies exist, but often show similar intraoperative and postoperative outcomes between the solutions. Some solutions, del Nido cardioplegia in particular, were found to have few or no significant human trials to back the rigor required in such a highly specialized field as cardiovascular surgery. A wide variation in the types of surgeries and primary outcomes were included in the publications, so it is difficult to perform an accurate systematic review of the topic.

Conclusion:

Uniform variables among different studies would be preferable for analysis of this topic; thus, it is the researchers’ recommendation that the collection of multicenter data be undertaken in order to more fully answer this research question. Comparative effectiveness studies to associate commonly used solutions are needed. Without this research, surgeon preference remains the primary determining factor for deciding which cardioplegic solution to use. Cardioplegia selection should rely more on higher scientific research, using evidenced-based medicine and ranking of clinical studies.

Custodiol versus blood cardioplegia in complex cardiac operations: an Australian experience

OBJECTIVES

A single or dual-dose strategy for myocardial protection is attractive in long operations, in avoiding the need to interrupt the procedure to re-administer cardioplegia. We hypothesized that a single administration of Bretschneider histidine-tryptophan-ketoglutarate (HTK) crystalloid solution (Custodiol) offers myocardial protection comparable with repeated tepid blood cardioplegia.

METHODS

We reviewed a prospectively compiled single-centre database containing all adult cardiac procedures performed from January 2005 to January 2011. Preoperative demographic and investigative data, operative variables and postoperative (30-day) mortality and morbidity were compared between the Custodiol and blood cardioplegia groups. The study primary endpoints were 30-day mortality, return to the operating theatre, myocardial infarction, stroke, postoperative requirement for an intra-aortic balloon pump, new renal failure, prolonged ventilation and re-admission to hospital within 30 days. Propensity score matching was performed to correct for any bias that may have been associated with the usage of Custodiol.

RESULTS

A total of 1900 cardiac surgical procedures were identified of which 126 (7%) utilized Custodiol and 1774 (93%) used blood cardioplegia as the primary cardioplegic agent. After propensity-score matching, we were able to match 71 Custodiol cases one-to-one to those receiving blood cardioplegia. There were no statistically significant differences noted for any of the endpoints studied after propensity-score matching. In particular, the proportion of mortality (blood cardioplegia: 1 vs Custodiol 4%, P = 0.63) any mortality/morbidity (blood cardioplegia: 35 vs Custodiol: 39% P = 0.46) was similar between the groups.

CONCLUSIONS

The use of Custodiol is convenient, simple and at least as safe as tepid blood cardioplegia for myocardial protection in complex cardiac operations. A randomized prospective comparison of myocardial protection strategies is warranted.

Single dose myocardial protection technique utilizing del Nido cardioplegia solution during congenital heart surgery procedures

BACKGROUND

The single dose cardioplegia technique for myocardial protection during congenital heart surgery is a viable alternative to multidose protocols.

METHODS

Thirty-four pediatric patients with aortic cross clamp times greater than 90 minutes were grouped by modified adult (MA) multidose solution or del Nido (dN) single dose solution. Also, data from eight patients where the cross clamp times were greater than two hours on one dose of dN solution were included.

RESULTS

In the 90-minute plus arm of the study, there were no significant differences between the groups when comparing the risk adjustment for congenital heart surgery (RACHS) (p=0.6), cardiopulmonary bypass times (CPB) (p=0.5), aortic cross camp times (p=0.5), weights (p=0.7) and number of intraoperative exogenous blood units (p=0.5). There were significant differences between the groups (p<0.05) in the number of cardioplegia doses and with perioperative glucose levels. In the greater than two hours group, the incidence of complete heart block (CHB) was 0.125% and there were no deaths or mechanical circulatory support (MCS) devices used.

CONCLUSION

del Nido cardioplegia solution is a reasonable tool for myocardial protection during congenital heart surgery that significantly decreased the number of cardioplegic interventions and perioperative glucose values in our study groups.

Histidine-tryptophan-ketoglutarate or celsior: which is more suitable for cold preservation for cardiac grafts from older donors?

BACKGROUND

The growing number of patients awaiting heart transplantation, coupled with the worldwide donor shortage, has led to increased use of marginal organs, specifically hearts from older donors. This study compared the protective effects of two widely used preservation solutions, histidine-tryptophan-ketoglutarate (HTK) and Celsior (CEL; Sangstat Medical, Menlo Park, CA), for ischemia-reperfusion injury using a rat heterotopic heart transplantation model with older donors.

METHODS

The hearts were excised from 16- and 80-week-old Lewis donor rats, stored in HTK, CEL, or saline for 6 hours and heterotopically transplanted into syngenic young Lewis recipients. Serum troponin I and creatine phosphokinase, graft infiltrating cells, graft apoptosis, graft proinflammatory messenger ribonucleic acid levels, and adenosine monophosphate-activated protein kinase phosphorylation were analyzed 3, 6, and 12 hours after reperfusion as markers of graft injury. Tissue adenosine triphosphate levels were measured after cold storage for 0, 6, 12, and 18 hours.

RESULTS

The HTK and CEL reduced injury comparably in grafts from young donors. The recipients of grafts from older donors and stored in HTK for 6 hours had lower levels of serum troponin I and creatine phosphokinase, less upregulation of the messenger ribonucleic acid for interleukin-6, intercellular adhesion molecule-1, and tumor necrosis factor-α, fewer infiltrating cells, less apoptosis, and less phosphorylated adenosine monophosphate-activated protein kinase than recipients of grafts stored in CEL. Adenosine triphosphate levels in the hearts stored in HTK were significantly higher than those stored in CEL or saline.

CONCLUSIONS

Cold storage in HTK exhibited superior protective effects against ischemia-reperfusion injury of hearts from older donors in this rat transplantation model.

The myocardial protection of HTK cardioplegic solution on the long-term ischemic period in pediatric heart surgery

Cardioplegic reperfusion during a long term ischemic period interrupts cardiac surgery and also increase cellular edema due to repeated administration. We reviewed the clinical experiences on myocardial protection of one single perfusion with histidine-ketoglutarate-tryptophan (HTK) for infants. This retrospective study included 118 infants who underwent open-heart surgery between January 2004 and December 2007. We divided the entire cohort into two groups: In group H (n = 63), myocardial protection was carried out with one single perfusion with HTK solution, and in group S (n = 55) with conventional St. Thomas crystalloid cardioplegia. The duration of cardiopulmonary bypass (CPB) did not differ between these two groups, but the duration of aortic cross-clamping time in group H was significantly shorter than that in group S (p < 0.05). During reperfusion, the spontaneous re-beating rate was higher in group H (p < 0.05). There were no differences in doses of inotropic agent and creatinekinase (CK) values on postoperative day 1 between these two groups, but the level of CK in group H was significantly less than that in group S on postoperative day 2 (p < 0.01). The mortality in group H was lower than in group S (p < 0.05). The HTK group had shorter cross-clamping time and more frequent spontaneous defibrillation than St. Thomas group. We propose that HTK is valid for some complicated cardiac surgeries with long term cross-clamping time.

Does the degree of cyanosis affect myocardial adenosine triphosphate levels and function in children undergoing surgical procedures for congenital heart disease?

OBJECTIVE

The outcome of children with cyanosis after cardiac surgical procedures is inferior to that of children who are acyanotic. Animal studies indicated detrimental effects of chronic hypoxia on myocardial metabolism and function. We studied whether the presence or the degree of cyanosis adversely affected myocardial adenosine triphosphate, ventricular function, and clinical outcome in children.

METHODS

Forty-eight children who underwent repair of tetralogy of Fallot were divided according to their preoperative saturation: group I, 90% to 100% (n = 14 patients); group II, 80% to 89% (n = 16 patients); and group III, 65% to 79% (n = 18 patients). Adenosine triphosphate was measured from right ventricular biopsy specimens taken before ischemia, at 15 minutes of ischemia, at end-ischemia, and at 15 minutes of reperfusion. Ejection fraction was measured by echocardiography.

RESULTS

Even before surgical ischemia, compared with groups I and II, group III had lower preoperative ejection fraction (59% +/- 2.9% vs 67% +/- 1.7% and 68% +/- 1.0%; P <.01) and lower preischemic adenosine triphosphate levels (15.1 +/- 2.1 vs 19.1 +/- 1.9 and 21.4 +/- 1.5 micromol/g dry weight; P <.01). After 15 minutes of ischemia, group III had lower adenosine triphosphate levels (11.2 +/- 1.8 vs 14.77 +/- 2.3 and 17. 6 +/- 3.1 micromol/g dry weight; P <.01). With reperfusion, both cyanotic groups lost further adenosine triphosphate compared with partial recovery in the acyanotic group (-22% +/- 3.8%, -20% +/- 3. 1% vs +18% +/- 1.8%; P <.01). Children in group III had a more complicated postoperative course as evidenced by longer ventilatory support (85 +/- 25 hours vs 31 +/- 15 and 40 +/- 21 hours; P =.07), inotropic support (86 +/- 23 hours vs 38 +/- 12 and 36 +/- 4 hours; P <.01), and intensive care unit stay (160 +/- 35 hours vs 60 +/- 10 and 82 +/- 18 hours; P =.02).

CONCLUSIONS

The degree of cyanosis adversely affects myocardial adenosine triphosphate, function, and clinical outcome of children who undergo cardiac operation. Children with cyanosis should be identified as a higher risk group that could be targeted for supportive interventions.

Prolonged preservation of the blood-perfused canine heart with glycolysis-promoting solution

BACKGROUND

Prolonged ischemia and inadequate myocardial preservation remain significant perioperative risk factors in cardiac transplantation. Long-term preservation techniques that have been effective in small rodent hearts have not been as effective in larger animal models or in clinical studies. We developed a cardioplegia solution formulated to promote high-energy phosphate production from glycolysis and determined its efficacy in a blood perfused canine heart model subjected to 24 hours of ischemia.

METHODS

Hearts harvested from adult dogs (n = 6 per group) were flushed with a histidine-buffered cardioplegia solution containing glucose or University of Wisconsin solution. The hearts were maintained at 4 degrees C for 24 hours then reperfused with autologous blood. After reperfusion, left ventricular pressures were measured with an intracavitary balloon at varying balloon volumes and compared with control nonischemic hearts. Predicted stroke volume and ejection fraction were calculated at an end-systolic pressure of 70 mm Hg and end-diastolic pressure of 15 mm Hg.

RESULTS

Developed pressure was better preserved in the hearts that received histidine-buffered solution (93+/-9 versus 38+/-7 mm Hg, p<0.05), along with a higher end-diastolic volume at 15 mm Hg (31+/-3 versus 22+/-2 mL histidine-buffered versus University of Wisconsin solutions, respectively, p<0.05). Stroke volume and ejection fraction were also higher in the histidine group (17+/-2.5 versus 2.3+/-1.2 mL and 50%+/-3.5% versus 9% +/-4.5%, respectively) in the presence of dobutamine.

CONCLUSIONS

The highly buffered glycolysis-promoting cardioplegia solution provided effective preservation of the blood perfused canine heart with superior recovery of pump performance after 24 hours of hypothermic ischemia compared with University of Wisconsin solution in this model.

Comparison of clinical outcome between histidine-triptophan-ketoglutalate solution and cold blood cardioplegic solution in mitral valve replacement

BACKGROUND

This study was conducted to compare the effect of histidine-triptophan-ketoglutalate solution (HTK) with that of cold blood cardioplegic solution (CBC) in mitral valve surgery.

METHOD

Forty-six patients who underwent mitral valve replacement between January 1994 and December 1996 were enrolled in this study. Twenty patients received HTK (HTK group), while 27 patients had CBC (CBC group) as myocardial protection. HTK was given as a single high dose, whereas CBC was used in the usual multidose format.

RESULT

The doses of inotropic agent at the end of extracorporeal circulation did not differ between the HTK group and the CBC group. Creatine kinase values (units) on day 1 and day 2 were 1140+/-412, 921+/-436 for the HTK group and 904+/-335, 816+/-420 for the CBC group, respectively (p = NS). Spontaneous defibrillation occurred in 26% of the CBC group and 90% of the HTK group (p < 0.05). Pacing was temporarily used in 20% of the HTK group and 44% of the CBC group after extracorporeal circulation (p < 0.05).

CONCLUSIONS

These results suggest that HTK provided more adequate myocardial protection in mitral valve surgery.

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.

Clinical assessment of prolonged myocardial preservation for patients with a severely dilated heart

BACKGROUND

The purpose of this study was to compare the myocardial protective effect of histidine-tryptophan-potassium and glucose-insulin-potassium cardioplegic solutions in patients with a dilated heart (left ventricular diastolic diameter > 55 mm, left ventricular systolic diameter > 45 mm) associated with prolonged cross-clamp time (longer than 200 minutes).

METHODS

We selected 20 patients with dilated hearts due to severe aortic regurgitation. Glucose-insulin-potassium cardioplegia was used in 11 patients and histidine-tryptophan-potassium cardioplegia was used in 9 patients.

RESULTS

After operation, the cardiac index was significantly increased in the histidine-tryptophan-potassium group (p < 0.05). Postoperative percent fractional shortening was 13.4% +/- 3.1% in the glucose-insulin-potassium group and 23.6% +/- 2.6% in the histidine-tryptophan-potassium group (p < 0.05). Creatine kinase levels were significantly lower in the histidine-tryptophan-potassium group than that in the glucose-insulin-potassium group (p < 0.05). The incidence of ventricular arrhythmia (higher than Lown's grade 2) was lower in the histidine-tryptophan-potassium group.

CONCLUSIONS

These data support the superiority of the histidine-tryptophan-potassium method over the glucose-insulin-potassium method for protection of the dilated heart during prolonged ischemia in open heart operations.

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.

Interstitial pH during myocardial preservation: assessment of five methods of myocardial preservation

We investigated changes in myocardial pH during cardioplegic arrest with five methods of preservation at 15 degrees +/- 1 degree C. Twenty-five dogs were subjected to cardiopulmonary bypass for 150 minutes. Group I (control) had hypothermia only. Group II received THAM-buffered blood cardioplegia, group III a bicarbonate-buffered blood cardioplegic solution, group IV infusions of hyperkalemic blood, and group V oxygenated St. Thomas 2 solution. After 120 minutes of ischemia, interstitial pH in group I was markedly depressed (6.4 +/- 0.07; p < 0.01). The pH in groups II and IV was well maintained (7.23 +/- 0.05 and 7.27 +/- 0.07) and differed significantly (p < 0.05) from that of the remaining groups. The pH in groups III and V was less well maintained (7.14 +/- 0.02 and 7.01 +/- 0.05), with no significant difference (p > 0.05) between these two groups. Postreperfusion functional recovery after 45 minutes was 24% +/- 6% in group I, 92% +/- 3% in group II, 82% +/- 5% in group III, 84% +/- 4% in group IV, and 66% +/- 6% in group V. Creatine kinase levels were significantly (p < 0.01) increased and ultrastructural damage was more prominent in group I compared with the remaining groups. Myocardial water content significantly increased in all groups. We conclude that a strongly buffered blood-based cardioplegic solution is more effective in preventing interstitial acidosis during moderate hypothermia and that maintenance of an optimal tissue pH plays an important role in postischemic functional recovery.

Oxygenation of cardioplegic solutions: a note of caution

The merits of oxygenated crystalloid cardioplegic solutions have been well established in experimental animals. The positive effects of oxygenation of Plasmalyte B (Sabax Ltd) and St. Thomas Hospital solution (Plegisol) were achieved by gassing with 95% O2/5% CO2 and 100% O2, respectively. In view of the marked pH differences induced by these gas mixtures, we evaluated the effect of mode of oxygenation on myocardial recovery during reperfusion after hypothermic cardioplegic arrest. Oxygenation with 100% O2 of Plasmalyte B containing high K+ levels caused marked deterioration in myocardial recovery, whereas the mode of oxygenation did not affect recovery after arrest with St. Thomas Hospital solution. Because the major differences between these solutions reside in their respective K+, Mg2+, and HCO3- contents, the effects of variations in the levels of these ions were investigated. The results showed that oxygenation with 100% O2 was deleterious only in the presence of high K+ (29 mmol/L), low Mg2+ (3 mmol/L), and high NaHCO3 (28 mmol/L) levels. The marked decline in mechanical recovery during reperfusion was associated with significant changes in myocardial adenosine triphosphate and intracellular Ca2+ levels. Although an explanation for these findings is not readily available, it is suggested that complex ionic interactions and possibly oxygen free radical generation may lead to intracellular Ca2+ overload, depression in mitochondrial adenosine triphosphate generation, and, hence, deterioration in mechanical recovery.

Upgrading acellular to sanguineous cardioplegic efficacy

To determine which biochemical entity of the red cell is responsible for preventing augmented postischemic myocardial oxygen consumption (MVO2), 28 canine hearts instrumented with ultrasonic dimension crystals underwent simultaneous determination of stroke work (SW) and MVO2 during incremental volume loading on right heart bypass before and 30 min after 2 hr of 10 degrees C cardioplegic arrest with unmodified oxygenated crystalloid cardioplegia (OC), OC with histidine of equal buffering capacity as 18% hematocrit blood (OC + H), or OC with 200 units/ml of superoxide dismutase and catalase (OC + SOD/C). In all groups, the slope of the linear SW vs end-diastolic volume relationship, Mw, and the slope of the linear SW vs MVO2 relationship, Me, were unchanged after cardioplegic arrest. The intercept of the SW vs MVO2 relationship, Eo, was augmented an average of 22.2% in the OC group, but both OC + H and OC + SOD/C prevented this subtle expression of ischemic injury. The characteristic of the red cell most likely responsible for the myoprotective efficacy of blood cardioplegia is buffering capacity; however, since the effects of tissue acidosis are partially mediated by free radicals, the use of free radical scavengers can also ameliorate ischemic damage incurred during cardioplegic arrest.

Myocardial salvage with trolox and ascorbic acid for an acute evolving infarction

Both Trolox (a water-soluble analogue of alpha-tocopherol) and ascorbic acid were more effective than superoxide dismutase or catalase in protecting myocyte cell cultures from free radical attack (induced by hypoxanthine and xanthine oxidase). In a canine model of two hours of left anterior descending coronary artery occlusion followed by four hours of reperfusion, Trolox and ascorbic acid reduced the area of infarction within the area at risk. The Trolox group received 500 mL of deoxygenated saline solution containing 2.0 g of Trolox, 3.0 g of ascorbic acid, and 18 mg of EDTA (ethylenediaminetetraacetic acid) infused into the ascending aorta 30 seconds before and four minutes after reperfusion. Saline controls received 500 mL of deoxygenated saline solution containing 18 mg of EDTA. The angioplasty group had unmodified reperfusion by simple release of the occlusion. The area at risk and the area infarcted were estimated with Evans blue and triphenyl tetrazolium hydrochloride stains, respectively. The ratio of the area infarcted to the area at risk was significantly lower with Trolox (angioplasty, 30.4% +/- 5.1%; saline, 20.8% +/- 2.9%; and Trolox, 8.7% +/- 4.0%; p less than 0.01). In summary, the antioxidants Trolox and ascorbic acid effectively reduced myocardial necrosis after ischemia.

Quantitation of postischemic skeletal muscle necrosis: histochemical and radioisotope techniques

Skeletal muscle necrosis will result from prolonged periods of ischemia. The purpose of this study was to develop a method to estimate the extent of necrosis using nitroblue tetrazolium staining and technetium scanning. The bilateral canine gracilis muscle preparation with total vascular isolation was exposed to 4 hr of complete normothermic ischemia followed by reperfusion. After 45 hr of reperfusion 99mTc pyrophosphate (PYP) was injected and 3 hr later the muscles were harvested, cut into six slices, and stained with nitroblue tetrazolium. Biopsies were taken from tetrazolium-positive and -negative areas for electron microscopy to confirm the ability of the stain to distinguish viable from necrotic muscle. Computerized planimetry of the staining pattern was used to estimate the extent of necrosis as a percentage of the total muscle. Electron microscopy confirmed the validity of nitroblue tetrazolium to discriminate between viable and necrotic skeletal muscle in this experimental model. After 4 hr of ischemia the percentage necrosis was 30.2 +/- 6.1% (mean +/- SEM, n = 12), there was no difference in the extent of necrosis in left vs right paired muscles, using tetrazolium staining or technetium PYP uptake. There was a statistically significant correlation between the percentage necrosis and the density of 99mTc PYP uptake per muscle (r = 0.83, P less than 0.001) and per slice (r = 0.94, P less than 0.001). This study demonstrates the ability of tetrazolium staining to accurately differentiate between viable and necrotic skeletal muscle and provides a reproducible method for estimating the extent of necrosis in the gracilis muscle model.