Transmural Left Ventricular Biopsy Research Articles

Acute stimulation of the soluble guanylate cyclase does not impact on left ventricular capacitance in normal and hypertrophied porcine hearts in vivo.

Experimental data indicate that stimulation of the nitric oxide-soluble guanylate cyclase(sGC)-cGMP-PKG pathway can increase left ventricular (LV) capacitance via phosphorylation of the myofilamental protein titin. We aimed to test whether acute pharmacological sGC stimulation with BAY 41-8543 would increase LV capacitance via titin phosphorylation in healthy and deoxycorticosteroneacetate (DOCA)-induced hypertensive pigs. Nine healthy Landrace pigs and 7 pigs with DOCA-induced hypertension and LV concentric hypertrophy were acutely instrumented to measure LV end-diastolic pressure-volume relationships (EDPVRs) at baseline and during intravenous infusion of BAY 41-8543 (1 and 3 μg·kg-1·min-1 for 30 min, respectively). Separately, in seven healthy and six DOCA pigs, transmural LV biopsies were harvested from the beating heart to measure titin phosphorylation during BAY 41-8543 infusion. LV EDPVRs before and during BAY 41-8543 infusion were superimposable in both healthy and DOCA-treated pigs, whereas mean aortic pressure decreased by 20-30 mmHg in both groups. Myocardial titin phosphorylation was unchanged in healthy pigs, but total and site-specific (Pro-Glu-Val-Lys and N2-Bus domains) titin phosphorylation was increased in DOCA-treated pigs. Bicoronary nitroglycerin infusion in healthy pigs ( n = 5) induced a rightward shift of the LV EDPVR, demonstrating the responsiveness of the pathway in this model. Acute systemic sGC stimulation with the sGC stimulator BAY 41-8543 did not recruit an LV preload reserve in both healthy and hypertrophied LV porcine myocardium, although it increased titin phosphorylation in the latter group. Thus, increased titin phosphorylation is not indicative of increased in vivo LV capacitance. NEW & NOTEWORTHY We demonstrate that acute pharmacological stimulation of soluble guanylate cyclase does not increase left ventricular compliance in normal and hypertrophied porcine hearts. Effects of long-term soluble guanylate cyclase stimulation with oral compounds in disease conditions associated with lowered myocardial cGMP levels, i.e., heart failure with preserved ejection fraction, remain to be investigated.

Metabolismo miocárdico após cardioplegia sangüínea hipotérmica retrógrada contínua com indução anterógrada normotérmica

OBJECTIVE: To determinate the alterations suffering by myocardium in the hypothermic retrograde continuous blood cardioplegia with antegrade warm cardioplegic induction. METHOD: A metabolic analysis of hypothermic retrograde continuous blood cardioplegia with antegrade warm cardioplegic induction was performed in a prospective study of 15 patients scheduled for elective coronary artery bypass grafting. Arterial and coronary sinus blood samples were simultaneously taken: before establishing cardiopulmonary bypass, after anterograde warm cardioplegic induction, when the aortic clamp was removed and 10, 30 and 60 minutes after reperfusion to analyze the oxygen content and lactate concentration. Four transmural left ventricular biopsy samples were obtained: before aortic clamping, immediately after the initial cardioplegia bolus, immediately before aortic declamping and 30 minutes after reperfusion to analyze the levels of ATP, ADP, AMP and lactate in the myocardium. The CK-MB isoenzyme was analysed in venous blood samples. RESULTS: There were no mortalities in the group. Inotropic support was not necessary in any patients and no peri- or post-operative myocardial infarction was detected. There was a decrease in the arterial-venous extraction of oxygen and lactate in the heart during reperfusion, a partial recovery occurred at 60 minutes of reperfusion. The levels of ATP and the other nucleotides in the myocardium were maintained during aortic clamping, but these levels decreased during the first 30 minutes of reperfusion. The lactate accumulated in the heart muscle during aortic clamping with a decrease occurring during reperfusion. CONCLUSIONS: From a metabolic point of view the method could not avoid an anaerobic metabolism during cross-clamping and only after 60 minutes of reperfusion there was a satisfactory metabolic recovery. These alterations are probably a reflection of cellular ischemic injury that occurs during cross-clamping and they seem to be of transitory effect. A better myocardium protection was observed with the addiction of anterograde warm induction cardioplegia.

Myocardial apoptosis prevention by radical scavenging in patients undergoing cardiac surgery

BackgroundReactive oxygen-derived species, including those generated during myocardial ischemia and reperfusion induced by cardioplegia, have been suggested to be involved in myocardial apoptosis induction. The purpose of our study was to investigate (1) whether cardioplegic arrest initiates apoptosis in the hearts of cardiac surgery patients and (2) whether reactive oxygen-derived species scavenging with N-acetylcysteine attenuates myocardial apoptosis initiation. MethodsIn transmural left ventricular biopsy samples collected before and at the end of cardiopulmonary bypass, we densitometrically determined cardiac myocyte staining intensity for active caspases-3 and -7, the apoptosis signal pathway central effector enzymes. The left ventricular biopsy samples had been obtained from 36 coronary artery bypass graft patients randomized in a double-blind fashion to receive either N-acetylcysteine (100 mg/kg into cardiopulmonary bypass prime followed by infusion at 20 mg · kg−1 · h−1; n = 18) or placebo (n = 18). ResultsThe change in left ventricular cardiac myocyte staining (end of cardiopulmonary bypass minus before cardiopulmonary bypass) differed significantly between groups for both measures: caspase-3, −3.1 ± 4.5 gray units (mean ± SD; N-acetylcysteine group) versus 7.1 ± 8.1 gray units (placebo); 95% confidence interval, 6.4 to 14.4; P < .0001; caspase-7, −5.1 ± 6.1 gray units (N-acetylcysteine) versus 5.1 ± 5.7 gray units (placebo); 95% confidence interval, 6.3 to 15.0; P < .0001. Clinical outcome did not differ between N-acetylcysteine and placebo. ConclusionsOur data show that cardioplegic arrest initiates the apoptosis signal cascade in human left ventricular cardiac myocytes. This apoptosis induction can effectively be prevented by N-acetylcysteine.

N-acetylcysteine prevents reactive oxygen species–mediated myocardial stress in patients undergoing cardiac surgery: results of a randomized, double-blind, placebo-controlled clinical trial

Objective Reactive oxygen species have been shown to contribute to myocardial stress in patients undergoing cardiac surgery, as demonstrated by myocardial 8-iso-prostaglandin-F 2α and nitrotyrosine formation. We hypothesized that the reactive oxygen species scavenger N-acetylcysteine attenuates reactive oxygen species–mediated myocardial stress in patients undergoing cardiac surgery. Methods Forty patients undergoing coronary artery surgery (mean age ± SD, 66 ± 9 years; 9 women and 31 men) were randomized to receive either N-acetylcysteine (100 mg/kg into cardiopulmonary bypass prime followed by infusion at 20 mg · kg −1 · h −1, n = 20) or placebo (n = 20). Patients and clinical staff were blinded to group assignment. Transmural left ventricular biopsy specimens collected before and at the end of cardiopulmonary bypass were subjected to immunocytochemical staining against 8-iso-prostaglandin-F 2α (primary measure) as an indicator for reactive oxygen species–mediated lipid peroxidation and nitrotyrosine (coprimary measure) as a marker for peroxynitrite-mediated tissue injury. Cardiomyocyte staining was quantitatively determined by using densitometry (in gray units). Global left ventricular function was measured on the basis of fractional area of contraction by using transesophageal echocardiography. Results Patient characteristics in both groups were comparable. The change in left ventricular cardiomyocyte staining (end of cardiopulmonary bypass − before cardiopulmonary bypass) differed significantly between groups for both primary measures: 8-iso-prostaglandin-F 2α, −1.8 ± 7.5 gray units (mean ± SD, N-acetylcysteine group) versus 5.0 ± 4.1 gray units (placebo group; 95% confidence interval, 2.6-11.0, P = .003); nitrotyrosine, −6.4 ± 10.0 gray units ( N-acetylcysteine group) versus 9.2 ± 8.4 gray units (placebo group; 95% confidence interval, 9.4-21.7, P < .001). Hemodynamics and clinical outcomes were comparable in both groups. Conclusions Reactive oxygen species scavenging with N-acetylcysteine attenuates myocardial oxidative stress in the hearts of patients subjected to cardiopulmonary bypass and cardioplegic arrest.

Nitrotyrosine and 8-isoprostane formation indicate free radical-mediated injury in hearts of patients subjected to cardioplegia

Objective: Myocardial ischemia and reperfusion induced by cardioplegic arrest subjects the heart to free radical-mediated stress. The purpose of our study was to investigate the effect of cardioplegia-induced ischemia and reperfusion on myocardial formation and distribution of (1) nitrotyrosine as an indicator for peroxynitrite-mediated tissue injury resulting from increased nitric oxide release and (2) 8-isoprostane as an indicator for oxygen-derived free radical-mediated lipid peroxidation. Methods: In 10 patients undergoing coronary artery operations (64 ± 6 [mean ± SD] years, 3 women and 7 men) subjected to cardiopulmonary bypass and intermittent cold blood cardioplegia, we collected transmural left ventricular biopsy specimens before and at the end of cardiopulmonary bypass. Specimens were cut at 10 μm and subjected to immunocytochemical staining against the nitric oxide-producing enzyme constitutive nitric oxide synthase, cyclic guanosine monophosphate (intracellular second messenger of nitric oxide), nitrotyrosine, and 8-isoprostane by using polyclonal antibodies. For global left ventricular function determination, we measured the fractional area of contraction using transesophageal echocardiography. Results: Nitric oxide synthase activity in cardiac myocytes increased from 34 ± 10 gray units before cardiopulmonary bypass to 47 ± 12 gray units at the end of bypass (P =.015), and all hearts showed increased cyclic guanosine monophosphate content in both myocytes and endothelial cells at the end of bypass. The number of nitrotyrosine-positive capillaries increased from 36 ± 29/mm2 before bypass to 82 ± 47/mm2 at the end of bypass (P =.012), and 8-isoprostane-positive capillaries increased from 92 ± 72/mm2 before bypass to 209 ± 108/mm2 at the end of bypass (P =.005). The fractional area of contraction was 53% ± 12% before bypass and 56% ± 12% after bypass (P =.47) but was slightly decreased to 45% ± 14% at 4 hours after bypass (P =.121). Conclusions: Our data show that cardioplegia-induced myocardial ischemia and reperfusion is associated with nitrotyrosine and 8-isoprostane formation mainly in the coronary endothelium, indicating injury mediated by both peroxynitrite and oxygen-derived free radicals. Because nitric oxide synthase activation was accompanied with increased cyclic guanosine monophosphate, these data suggest that direct effects of nitric oxide on cardiac myocytes, as well as nitric oxide-mediated coronary endothelial injury, might contribute to injury associated with cardioplegia and cardiopulmonary bypass.J Thorac Cardiovasc Surg 2003;125:178-83

Variations in collagen content of asynergic left ventricular segments in explanted hearts of men with ischemic cardiomyopathy

Transmural left ventricular (LV) biopsies obtained at the time of coronary artery surgery have been used to evaluate the histomorphologic features of viable myocardium in patients with ischemic cardiomyopathy. 1–16 Usually, 1 or 2 biopsies are obtained from the center of the LV region supplied by the left anterior descending coronary artery. The biopsy specimens (1.2 to 1.5 mm in diameter) are subsequently used for quantifi cation of collagen using grids with visual point counting. 1–16 The degree of myocardial fi brosis in these biopsy samples has been correlated with the results of various noninvasive tests used for assessment of preoperative regional myocardial viability. However, it is unclear whether the data obtained from these transmural biopsy samples would uniformly refl ect the overall histomorphologic features of the entire LV region as evaluated by noninvasive imaging techniques. In this study, we determined the extent of variation in volume fraction of collagen of 2-mm-wide (biopsy-equivalent) consecutive transmural sections of mid-LV anterior wall from explanted hearts of men with chronic ischemic heart disease. Moreover, we examined the variability of fi brosis in normal, ischemic, and scarred myocardium as assessed by thallium.  The 13 men with ischemic cardiomyopathy awaiting cardiac transplantation were prospectively enrolled in a study determining the relation of thallium uptake to myocardial fi brosis. 17 Patients’ ages ranged from 41 to 62 years (mean 54). All patients had severe (New York Heart Association functional class III to IV) heart failure and/or angina pectoris and multivessel coronary artery disease, and were listed as stable outpatients at the time of enrollment. Patients with recent acute myocardial infarction or unstable angina were excluded from the study. Cardiac transplantation was performed at a mean of 6 2 months after the nuclear imaging studies. The explanted hearts were fi rst fi xed in formaldehyde. The left ventricle was then sliced transversely at a mean thickness of 8 mm/slice from apex to base. A mid-LV slice was divided into 8 large segments. The 2 large segments representing the anterior wall were then embedded in paraffi n, cut at a thickness of 5 m and stained with picrosirius red. These segments were further divided into consecutive 2-mmwide transmural sections. Percent collagen was then quantifi ed using a computerized image analysis system (Quantimet 520, Cambridge, Massachusetts) in the large segments and in each small section, as previously described. 18 All patients underwent stress-redistribution-reinjection thallium single-photon emission computed tomography. Short-axis tomograms at the mid left ventricle, corresponding to that used for the histomorphologic study, from the 3 sets of thallium images (stress, redistribution, and reinjection) were analyzed objectively, using a semiautomated quantitative circumferential profi le as previously described. 19 Briefl y, for each patient, an operator-defi ned region of interest was drawn around the LV activity of each short-axis slice on the corresponding stress, redistribution, and reinjection images. As with the histologic assessment, the myocardial activity was divided into 8 segments of equal arcs, beginning at the center of the anterior LV wall and proceeding clockwise. Mean counts per pixel within the 2 anterior wall segments (anteroseptal and anterolateral) on stress, redistribution, and reinjection images were computed. The myocardial segment with the highest thallium activity on the stress tomogram was used as the normal reference segment. The same segment in redistribution and reinjection thallium

Myocardial ischemic injury and purine metabolism in patients undergoing coronary artery bypass.

High-energy phosphates and their catabolic products were determined in myocardium during coronary artery bypass surgery with blood cardioplegic reperfusion in order to evaluate the effects of aortic cross-clamping and reoxygenation on myocardial purine metabolism. Transmural left ventricular biopsy specimens were taken with ITu-Cut biopsy needles, before aortic cross-clamping, before cross-clamp removal and after 30' of reperfusion; perchloric extracts of the material were analyzed for nucleotide content by capillary zone electrophoresis (CZE). The CZE procedure used separates the complete spectrum of purine metabolites in myocardial extracts obtained from 0.6-8.6 mg biopsy material. The basal values of ATP/ADP ratio and energy charge were low, IMP content was high. After the ischemic period, ATP levels further decreased and IMP, nucleosides and bases accumulated. After reperfusion, nucleoside and base basal levels, but not energy charge, were restored to some extent. The study arises the problem of myocardial preservation during heart surgery. In this investigation, capillary electrophoresis was an extremely adaptable technique for the evaluation of ischemic injury and could be useful in studying the effects of cardioplegic solutions.

Relation between left ventricular function and oxidative stress in patients undergoing bypass surgery

ObjectiveTo determine whether preoperative left ventricular ejection fraction (LVEF) is related to the degree of myocardial oxidative stress during bypass surgery in man.DesignObservational study.SettingTertiary care centre.Patients and interventions31 patients (LVEF...

Phosphorylation of Tyrosine 182 of p38 Mitogen-activated Protein Kinase Correlates with the Protection of Preconditioning in the Rabbit Heart

p38 mitogen-activated protein kinase (MAPK) is known to be activated after exposure to endotoxin, osmotic and environmental stress, and, most recently, during ischemia/reperfusion. We investigated whether ischemic preconditioning also causes phosphorylation of the activation sites on p38 MAPK. Three groups of isolated rabbit hearts were studied. Control hearts experienced 30 min of ischemia only. The second group was preconditioned with 5 min of global ischemia and 10 min of reperfusion. Group 3 was also ischemically preconditioned, but in the presence of 100μm8-(p-sulfophenyl)theophylline (SPT). Transmural left ventricular biopsies were taken before and during the long ischemic period. Western blot analysis with either p38 MAPK or phospho-specific p38 MAPK (Tyr-182) antibodies showed a decreased phosphorylation during ischemia in non-preconditioned hearts, but phosphorylation was enhanced several fold after 10 and 20 min of ischemia in preconditioned hearts. Furthermore, when protection from ischemic preconditioning was blocked by SPT, increased phosphorylation of p38 MAPK during ischemia was not present. Therefore the phosphorylation of p38 MAPK at tyrosine 182, which is required for the kinase's activation, occurred during ischemia only when protection from preconditioning was evident. In a second study, changes in osmotic fragility were measured during simulated ischemia in rabbit cardiomyocytes. Reduced fragility in ischemically preconditioned myocytes could be completely abolished by the specific p38 MAPK inhibitor SB-203580. In contrast, anisomycin, an activator of p38 MAPK and JUN kinase pathways, was found to be as protective as ischemic preconditioning. We conclude that p38 MAPK phosphorylation correlates with preconditioning's protection, and that its activation may be an important step in the signal transduction cascade of ischemic preconditioning.

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. (Ann Thorac Surg 1997;63:98–104)

Cardioprotective Effects of Carnitine in Extensive Aortocoronary Bypass Grafting

The cardioprotective effects of carnitine were tested in patients undergoing multiple aortocoronary bypass grafting. Intermittent aortic cross-clamping at 28 degrees C was used. Mean total cross-clamping time was 30 +/- 11 min. Patients were randomized into three groups: a control group receiving placebo (group 1), a group pretreated with 3 g carnitine intravenously before cardiopulmonary bypass (CPB) (group 2), and a group pretreated with 6 g carnitine intravenously (group 3). The markers of myocardial ischemia included levels of adenosine triphosphate, its catabolites, and creatine phosphate in transmural left ventricular biopsy specimens taken at the beginning and end of CPB, as well as hemodynamic recovery during weaning from CPB and for the next 24 h. The intravenous infusion of carnitine (3 or 6 g) had no hemodynamic effect. At the end of CPB myocardial tissue levels of adenosine triphosphate and creatine phosphate did not differ significantly among the groups (P greater than 0.05). Recovery of cardiac function during weaning from CPB and for the following 24 h was similar in all three groups (P greater than 0.05). It is concluded that pretreatment with carnitine neither facilitates weaning from cardiopulmonary bypass in patients undergoing aortocoronary bypass surgery nor favorably affects hemodynamic function during the next 24 h.

Accelerated transmural gradients of energy compound metabolism resulting from left ventricular hypertrophy

Eighteen dogs underwent transmural left ventricular biopsies for adenosine triphosphate and suturing of the noncoronary cusp, creating valvular aortic stenosis. Three months after aortic stenosis and the subsequent development of left ventricular hypertrophy, animals underwent repeat transmural left ventricular biopsies followed by total myocardial ischemia at 37 degrees C. Left ventricular tissue samples for adenosine triphosphate and lactate levels were determined at 15-minute intervals and compared with 15 control animals. No significant difference between subendocardial and subepicardial adenosine triphosphate levels was found between left ventricular samples taken before left ventricular hypertrophy and 3 months after left ventricular hypertrophy. Significant differences in adenosine triphosphate utilization occurred between subendocardial and subepicardial layers in control and left ventricular hypertrophy myocardium, however. The gradient between the subendocardium and the subepicardium was significantly increased by left ventricular hypertrophy (p less than 0.05). Significant differences also occurred within the same layer when left ventricular hypertrophy and control groups were compared. During total ischemia, lactate concentration was significantly greater within the subendocardium than within the subepicardium in left ventricular hypertrophy. The onset of ischemic contracture was 48.2 +/- 2.1 minutes in left ventricular hypertrophy versus 62.3 +/- 1.8 minutes in control hearts (p less than 0.01). Subendocardial intramyocardial pressure increased significantly earlier than subepicardial in both left ventricular hypertrophy and control hearts. Adenosine triphosphate was used, and lactate accumulated more rapidly in animals with a more pronounced hemodynamic gradient. These data show that after left ventricular hypertrophy, adenosine triphosphate stores in the subendocardium and the subepicardium are unchanged from control values, yet the rates of adenosine triphosphate utilization and lactate accumulation during total ischemia are significantly increased. Furthermore, the subendocardial to subepicardial gradient of adenosine triphosphate utilization during ischemia found in normal hearts is markedly increased by left ventricular hypertrophy.

Nifedipine as an adjunct to St. Thomas’ Hospital cardioplegia: A double-blind, placebo-controlled, randomized clinical trial

The cardioprotective effect of the addition of the slow calcium-channel blocker nifedipine to cardioplegic solution was tested in two double-blind placebo controlled randomized studies. The first study included 24 patients undergoing aortic-coronary bypass grafting, and the second included 24 patients undergoing aortic valve replacement. Nifedipine at a dose of 200 micrograms/L or placebo was added to St. Thomas' Hospital cardioplegic solution. The following markers of ischemia were used: adenosine triphosphate and its catabolites, creatine phosphate and inorganic phosphate, determined in transmural left ventricular biopsy specimens taken before, at the end of, and after aortic cross-clamping; hemodynamic recovery 15 minutes after cessation of cardiopulmonary bypass; clinical outcome in terms of the incidence of arrhythmias, low cardiac output, positive inotropic support immediately after operation, and follow-up at 15 months. The main difference between the two studies was that myocardial temperature during cross-clamping remained constant at 14 degrees C in coronary bypass grafting but increased to 25 degrees C in valve operations despite the application of the same amounts of cardioplegic solutions. This lower temperature resulted in better preservation of high-energy phosphates in coronary bypass operations as compared to the placebo group having valve replacement operations. According to analysis of variance, a drug effect could be demonstrated only in the aortic valve replacement study: Accumulation of breakdown products of the adenine nucleotide pool was less in the nifedipine group than in the placebo group (p less than 0.05). Adenosine triphosphate decreased only to 84% in the nifedipine group and to 72% in the placebo group. Despite this adenosine triphosphate-sparing effect, weaning from cardiopulmonary bypass was more difficult in the nifedipine group. Left ventricular stroke work index 15 minutes after bypass was decreased to 72% of the prebypass value in the nifedipine group (t test, p less than 0.01) and only to 86% in the placebo group (p = NS). In contrast, after the patients were admitted to the intensive care unit, the incidence of low cardiac output tended to be lower in the nifedipine group than in the placebo group: 33% versus 58% (p = NS). In conclusion, ischemia-induced degradation of nucleotides as it occurs when myocardial cooling is inadequate can be prevented by the addition of nifedipine to the St. Thomas' Hospital cardioplegic solution. This effect, however, is not associated with an improved clinical outcome.

Ultrastructural Myocardial Preservation During Coronary Artery Surgery: A Controlled, Prospective, Randomized Study in Humans

Potassium cardioplegia was compared with normothermic, intermittent ischemic arrest in 30 patients undergoing multiple coronary artery bypass grafts. Group 1 comprised 15 patients in whom cold potassium cardioplegia with St. Thomas' Hospital solution was used. In Group 2 were 15 patients who underwent intermittent ischemic arrest during the construction of the distal anastomoses. Two myocardial transmural left ventricular biopsies were done in each patient. There was no operative mortality. Electron microscopical examination showed normal myocardial ultrastructure in both groups. In particular, mitochondria were well preserved in all samples. The postoperative electrocardiogram demonstrated a new Q wave in 1 patient in Group 2 whose level of the myocardial isoenzyme of creatine phosphokinase (CPK-MB) was within the normal range. The peak CPK-MB release in Group 1 was 23.2 ± 20.1 IU and in Group 2, 19.9 ± 15.1 IU. This difference was not statistically significant. The mean period of anoxic arrest in Group 1 was 49.5 ± 15 minutes and in Group 2, 25.5 ± 8 minutes ( p < 0.001). Total cardiopulmonary bypass time in Group 1 was 114.5 ± 20 minutes and in Group 2, 90.2 ± 16 minutes ( p < 0.01). It is concluded that both techniques can preserve myocardial subcellular architecture during multiple coronary artery bypass grafting in patients with normal left ventricular function.

Intermittent aortic cross-clamping versus St. Thomas’ Hospital cardioplegia in extensive aorta-coronary bypass grafting: A randomized clinical study

Myocardial preservation was assessed in 72 patients undergoing extensive myocardial revascularization. The patients were allocated at random to three surgical techniques: Group 1, intermittent aortic cross-clamping at 32 degrees C; Group 2, intermittent aortic cross-clamping at 25 degrees C; and Group 3, St. Thomas' Hospital cardioplegia. As intraoperative markers of ischemic damage, adenosine triphosphate, creatine phosphate, and glycogen contents were determined in transmural left ventricular biopsy specimens taken at the beginning and at the end of cardiopulmonary bypass. Ultrastructure was studied in a similar pair of biopsy specimens. Release of myocardium-specific creatine kinase isoenzyme was determined intraoperatively and postoperatively. Functional recovery was assessed before and after weaning from cardiopulmonary bypass. The incidence of low cardiac output, myocardial infarction, and rhythm disturbances was compared between groups. Finally, actuarial survival and event-free curves were studied after 18 months' follow-up. The results show a better preservation of high-energy phosphates, glycogen, and ultrastructure in the cardioplegia group as compared to the two cross-clamp groups. However, severe myocardial damage was never observed. Release of MB creatine kinase isoenzyme was the same in all three groups. Functional recovery of the hearts immediately after cessation of cardiopulmonary bypass was better in the cardioplegia group, but the incidence of rhythm disturbances (atrioventricular conduction problems) was higher in the cardioplegia group than in the other two groups (p less than 0.05). Clinical outcome in terms of incidence of perioperative infarction, survival, and event-free follow-up was not different between groups. It is concluded that both techniques (aortic cross-clamping at 32 degrees C or 25 degrees C and St. Thomas' Hospital cardioplegia) offer good myocardial protection in extensive aorta-coronary bypass operations. St. Thomas' cardioplegia, however, in contrast to intermittent aortic cross-clamping, prevents the onset of ischemia-induced deterioration of cardiac metabolism, i.e., destruction of the adenine nucleotide pool.

Cardioprotective effects of lidoflazine in extensive aorta-coronary bypass grafting

The cardioprotective effects of lidoflazine, a calcium entry blocker, were tested in patients undergoing multiple aorta-coronary bypass grafting (at least four grafts). Intermittent aortic cross-clamping at 25 degrees to 28 degrees C was used. Mean cross-clamp time was 11 minutes for one distal anastomosis. Patients were randomized into three groups: a control group (I), a group (II) pretreated with 0.5 mg . kg-1 lidoflazine intravenously before cardiopulmonary bypass (CPB), and a group (III) pretreated with 1 mg . kg-1 lidoflazine intravenously. The following markers of ischemia are used: (1) adenosine triphosphate (ATP), creatine phosphate (CP) and glycogen determined in transmural left ventricular biopsy specimens taken at the beginning and end of CPB; (2) ultrastructure in a similar pair of specimens; and (3) hemodynamic recovery 15 minutes after cessation of CPB. At the end of the intervention, ATP decreased to 73% in Group I but remained unchanged in Groups II (98%) and III (88%). CP decreased to 82% in Group I and remained unaltered in Groups II (100%) and III (110%). Glycogen decreased in Group I (to 44%) and in Group II (78%) but remained unchanged in Group II (138%). Ultrastructural study showed better preservation of the glycocalyx and sarcolemma in Group III than in Group I. Left ventricular stroke work index remained unaltered after CPB in Group III but decreased in Groups I and II to about 60% of its initial value. Thus lidoflazine pretreatment protects the myocardium in a dose-dependent manner against deterioration of myocardial function and structure.

Preservation of Myocardial ATP: Comparison of Blood vs Crystalloid Cardioplegia

Preservation of myocardial high-energy phosphates correlates with the heart's ability to resume normal function following aortic crossclamping (AXC). The ability of the canine myocardium to synthesize and maintain ATP during 180 minutes of AXC was evaluated in 12 hearts subjected to either blood or crystalloid cardioplegic arrest. Group 1 hearts were arrested by infusion of 750 ml of blood potassium cardioplegia (BKC) solution into the aortic root initially and every 30 minutes, as were group 2 (six) hearts but with a crystalloid cardioplegia (CC) solution. Transmural left ventricular biopsy specimens were obtained for ATP analysis prior to AXC (control), before and after cardioplegia injections 2, 4, and 6, prior to unclamping (180 minutes of AXC), and 30 minutes following reperfusion. ATP levels increased significantly above control (p less than 0.005) during the 180 minutes of AXC immediately following infusion of BKC. At the end of 180 minutes of AXC and following 30 minutes of reperfusion, ATP was noted to be normal in this group (p = NS). In contrast, ATP levels fell significantly (p less than 0.005) during the period of aortic cross-clamping in the crystalloid cardioplegia group and did not return to normal even after 30 minutes of reperfusion (p less than 0.005). We concluded that BKC, by presenting the arrested myocyte with adequate oxygen and substrate, allows for synthesis and preservation of myocardial ATP during periods of AXC as long as three hours. In this respect, it should be regarded as superior to CC, which permits a statistically significant depletion of ATP (p less than 0.005) uncorrected, even after 30 minutes of reperfusion in the beating, nonworking state.

Depressed high-energy phosphate content in hypertrophied ventricles of animal and man: the biologic basis for increased sensitivity to ischemic injury.

It is frequently stated that hypertrophied ventricles tolerate ischemia less well than nonhypertrophied ventricles. The authors' earlier studies in a rat supravalvular aortic stenosis model and canine valvular aortic stenosis model, both with concentric left ventricular hypertrophy, disclosed accelerated rates of ischemic contracture and diminished basal myocardial high energy phosphate stores. These studies have been extended to ten patients with severe left ventricular hypertrophy caused by valvular aortic stenosis and normal coronary arteries. ATP (endocardial and epicardial) from transmural left ventricular biopsies taken at operation before aorta cross-clamping, and frozen immediately in liquid nitrogen, were compared with similar biopsies from patients with nonhypertrophied myocardium supplied by normal coronary arteries. The subendocardial high energy phosphate levels in the nonhypertrophied myocardium was greater than high energy phosphate levels in the subepicardium of nonhypertrophied ventricles (ATP-micromoles/gram-protein, epi = 36.8 +/- 3.3, endo = 37.7 +/- 3.3) (p = NS). However, in the hypertrophied myocardium the subendocardium consistently showed significantly depressed high-energy phosphate levels when compared with subepicardial levels (ATP-hypertrophied myocardium, epi = 31.5 +/- 1.6, endo = 25.9 +/- 1.7) (p less than 0.05). This uniform depression of ATP stores, greatest in the subendocardium, in left ventricular hypertrophy suggests a common biologic mechanism for the enhanced sensitivity to ischemia. Of importance for patients may be the prior observation in rats that repletion of ATP( stores before ischemia eliminates the accelerated rate to ischemic contracture. Diminished subendocardial ATP stores appear to be an intrinsic property of severely hypertrophied myocardium and probably contribute to its enhanced sensitivity to ischemia.

Characterization of the lateral interface between normal and ischemic tissue in the canine heart during evolving myocardial infarction

A new nonrotating multiple biopsy device has been developed to allow the rapid, simultaneous and contiguous sampling of cardiac muscle in the large mammalian heart. Each cutter obtains 40 adjacent transmural left ventricular biopsy samples, each of 4 mm section. The epicardial 1.8 mm of each biopsy section was analyzed for flow, adenosine triphosphate, adenosine diphosphate, adenosine monophosphate, creatine phosphate and lactate. Use of this procedure in the dog heart 30 minutes after coronary arterial ligation permitted characterization of the nature of flow and metabolic gradients as the sampling site moved from the core of an area of regional ischemia to the surrounding normal tissue. These studies of metabolic and flow geometry in the lateral plane Indicate the existence of a sharp interface of flow and metabolism between normal and ischemic tissue. The absence of intermediate levels of flow and metabolism indicate that, in the lateral plane at least, a quantitatively significant and spatially identifiable “border zone” region does not exist. However, these findings, do not preclude the existence of such a zone of jeopardized tissue in the transmural plane or the occurrence of a temporal border zone to which interfaces of flow and metabolism may migrate with time.

St. Thomas Cardioplegia Versus Topical Cooling: Ultrastructural and Biochemical Studies in Humans

Transmural left ventricular biopsies were studied from 28 patients undergoing cardiopulmonary bypass with anoxic cardiac arrest. The myocardium was protected by topical cooling (20° C) (Group 1, 15 patients) or by cardioplegia with St. Thomas' solution (Group 2, 13 patients). Biopsies were taken at the start of bypass and 3 to 5 minutes after unclamping of the aorta. Mean cross-clamp time was not significantly different between the groups (50 minutes for Group 1 and 53 minutes for Group 2; p > 0.05). The ultrastructural changes induced by ischemia and subsequent reperfusion were almost exclusively related to the mitochondria. The degree of mitochondrial damage was evaluated by a semiquantitative analysis based on mitochondrial fine structure. The frequency of severe postischemic mitochondrial damage was significantly higher in Group 1 (20.1% verus 2.7% in Group 2; p < 0.05). Biochemical analysis of the biopsies indicates that the myocardial concentration of creatine phosphate decreases by about 50% after topical cooling ( p < 0.05). With St. Thomas cardioplegia, no significant change in the tissue level of this high-energy phosphate takes place. The results show evidence of the superiority of the St. Thomas cardioplegia to topical cooling alone.