Quantitative evaluation of myocardial ultrastructure following hypothermic anoxic arrest

Successful cardiac presrevation for 12 hours using nondepolarizing cold cardioplegia. A canine model

Isolated canine hearts were preserved for 12 h at 5 degrees C followed by normothermic reperfusion for 2 h. Dogs were divided into two groups: group 1 (n = 7) received a nondepolarizing preservation solution in multidose, and group 2 (n = 6) received single-flushed University of Wisconsin (UW) solution, both administered in multidose fashion. At the end of reperfusion, the myocardial adenosine triphosphate concentration and left ventricular systolic and diastolic function were preserved better in groupl than in group 2. Myocardial mitochondrial ultrastructural integrity was identical in the two groups. These results suggested that in a 12-h heart preservation, nondepolarizing solution administered in multidose fashion protects the myocardium from the deleterious effects of hypothermia and cardioplegia better than UW solution.

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.

Effect of pinacidil on rat hearts undergoing hypothermic cardioplegia

We studied the effect of pinacidil, a potassium-channel opener, on the hemodynamic, biochemical, and ultrastructural changes in rat hearts undergoing hypothermic cardioplegia. Fifty-four male Wistar rats weighing 250 to 300 g were used. Isolated hearts were prepared for modified Langendorff circulation in the working mode using modified Krebs-Henseleit bicarbonate solution bubbled with a 95% O2 and 5% CO2 gas mixture. Eighty minutes of cardioplegia at 25 degrees C was followed by normothermic reperfusion for 30 minutes. Pinacidil, 5, 10, or 50 mumol/L added to the cardioplegic solution, did not affect heart rate, but is significantly improved the recovery of aortic flow as compared with controls (88.1% +/- 4.3 [5 mumol/L]; 83.2% +/- 8.5% [10 mumol/L]; 90.3% +/- 5.3% [50 mumol/L] compared with 55.6 +/- 4.3% [control]; p < 0.05). Administration of pinacidil during reperfusion did not further enhance the recovery of aortic flow. The dose-response curve of aortic flow to the pinacidil concentrations was flat from 5 to 50 mumol/L. However, preservation of myocardial adenosine triphosphate and calcium concentrations and mitochondrial morphology suggested that the optimal concentration of pinacidil cardioplegia is 10 mumol/L.

The effects of a temperature below 15 degrees C on the myocardial calcium and ultrastructure in donor heart preservation in a canine model

The effects of 6-h hypothermic cardioplegic arrest on myocardial biochemical, morphologic, and functional recovery were investigated in two groups of dogs. Group 1 (n = 6) was subjected to hypothermia of 15 degrees C and group 2 (n = 6) was subjected hypothermia of 5 degrees C. Although the myocardial calcium (Ca) concentration was significantly higher at the end of reperfusion in group 2 compared to group 1, the MB-fraction of creatine kinase, mitochondrial aspartate aminotransferase, recovery of left ventricular systolic function, and mitochondrial morphologic integrity were better in group 2 than in group 1. These findings suggest that hypothermia of 5 degrees C in 6-h cardioplegia is not necessarily coupled with interference in myocardial contractility, despite the Ca overload that occurs during reperfusion.

The effect of betamethasone on myocardial viability during cold cardioplegia in canine donor heart preservation

This study examined the effect of betamethasone on myocardial viability of reperfused isolated canine hearts following a 6-h hypothermic cardioplegia. The dogs were divided into two groups: group I (n = 9) received nondepolarizing cardioplegia containing betamethasone 250 mg/l while group II (n = 7) was administered cardioplegia without betamethasone. The myocardial concentrations of calcium, ATP, ADP, total adenine nucleotide, cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) were identical in the two groups throughout the experiment. The coronary sinus plasma concentrations of MB fraction of creatine kinase (MB-CK), cAMP and cGMP after 2h of reperfusion were significantly lower in group I than in group II. The myocardial mitochondrial ultrastructure, as assessed by semiquantitative morphometry, was found to be significantly better preserved in group I than in group II at the end of both preservation and reperfusion. In addition, the left ventricular end-systolic pressure volume relation (ESPVR) showed a higher slope and lower intercept in group I than in group II. These results suggest that the addition of betamethasone to nondepolarizing cold cardioplegia enhances myocardial protection via membrane stabilization without affecting the adenine nucleotide metabolism.

Effects of catecholamines on myocardial viability in early reperfusion following hypothermic global ischemia in dogs--comparison between epinephrine and dobutamine

Attempts were made to define the effects of epinephrine and dobutamine on the myocardium during early reperfusion for 60 minutes following hypothermic global ischemia at a myocardial temperature of 28 degrees C for 60 minutes under cardiopulmonary bypass. Ischemia was induced by cross-clamping the dog aorta. Epinephrine (0.1 microgram/kg/min) and dobutamine (5 micrograms/kg/min) were given throughout the reperfusion period by intravenous drip infusion, a control group was treated with saline infusion. Comparison of hemodynamic parameters was made before cardiopulmonary bypass, and at 30 and 60 minutes of reperfusion. Epinephrine and dobutamine significantly increased stroke volume index, left ventricular stroke work index and tissue calcium content compared with saline, however, myocardial water content was only slightly higher in the group given saline, compared with the other two groups. Myocardial mitochondrial membranes and cristae were slightly damaged and creatine phosphate content was reduced. Ultrastructural integrity was related to myocardial tissue calcium content, with a significant negative correlation. These results suggest that epinephrine (0.1 microgram/kg/min) will improve stroke volume index and left ventricular stroke work index, as does dobutamine (5 micrograms/kg/min), however, both agents had a minimal effect on reducing myocardial morphological and biochemical integrity, although catecholamines have detrimental effects on the myocardium in early reperfusion following ischemia.

Comparison of the effectiveness of myocardial preservation in right atrium and left ventricle

Ten patients underwent cardiac operations during which myocardial preservation was provided by systemic hypothermia, topical cardiac cooling, and cold blood cardioplegia. The duration of ischemia ranged from 45 to 142 minutes (mean, 84.2 +/- 36.2 minutes). Two serial specimens (preischemic and ischemic) were obtained from the right atrium and the left ventricle, respectively; thus, a total of 40 biopsy specimens was obtained from these 10 patients. A combination of grading of ischemic injury and stereological morphometric measurement of mitochondria was performed to assess the effectiveness of myocardial preservation. Our findings from the mitochondrial score studies (grading of ischemic injury) were as follows. In the right atrium, the average mitochondrial score rose from 0.337 +/- 0.235 in the preischemic stage to 1.969 +/- 0.492 in the ischemic stage. In contrast, the average mitochondrial score for the left ventricle was only elevated from 0.380 +/- 0.161 to 1.353 +/- 0.396. The difference between preischemia of the right atrium and left ventricle is not statistically significant, but the difference between ischemia of these chambers is significant (p less than 0.01). Our stereological morphometric studies revealed that in the left ventricle, the average mitochondrial surface area was 0.316 +/- 0.046 micron 2 in the preischemic stage and 0.347 +/- 0.073 micron 2 in the ischemic stage, a 9.8% increase in mitochondrial size (not significant). In contrast, the mitochondrial surface area of the right atrium showed a mean increase of 65.8%, from 0.231 +/- 0.038 micron 2 in the preischemic stage to 0.383 +/- 0.057 micron 2 in the ischemic stage (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Intramyocardial temperature following various cooling procedures

In 12 dogs on cardiopulmonary bypass, the intramyocardial temperatures in the anterior and the posterior wall of the left ventricle and in the septum were measured with microthermoelectrodes when different cooling procedures were used during 60 min of anoxic cardiac arrest. External cooling with 4 degrees C glucose (5.5%) solution dripping into the pericardial sac did not lower the temperature in the septum or in the posterior wall. Packing the heart in slushed ice after injection of the same glucose solution into the coronary tree reduced the septum and posterior wall temperature to around 30 degrees C. This cooling procedure, in combination with general moderate hypothermia, lowered the temperature to about 20 degrees C in these parts of the heart. Only when combined with general hypothermia did local cooling achieve low temperatures in all regions of the myocardium.

Superior action of magnesium-lidocaine-1-aspartate cardioplegia to glucose-insulin-potassium cardioplegia in experimental myocardial protection

The effect of 2 hours of hypothermic Mg-lidocaine cardioplegia upon left ventricular function, myocardial high-energy stores, edema, and ultrastructure was studied as compared to glucose-insulin-potassium (GIK) cardioplegia in 12 mongrel dogs. The myocardial temperature recorded in the ventricular septum was kept at 20 degrees C during the cardioplegia. The heart was re-warmed up to 37 degrees C by the support of cardiopulmonary bypass, then, observations were made during a 60 minutes reperfusion. Left ventricular function was preserved at a more physiological level in cases of Mg-lidocaine cardioplegia. Myocardial ATP as preserved at significantly higher levels following Mg-lidocaine cardioplegia than in cases of GIK cardioplegia (p < 0.05). However, content of myocardial creatine phosphate was higher in the GIK cardioplegia group than that in Mg-lidocaine group in the subendocardium and the ventricular septum. Myocardial edema was significantly suppressed following Mg-lidocaine cardioplegia, and such was significantly lower than in cases of GIK cardioplegia (p < 0.05). The myocardial ultrastructure was protected from ischemic insult in the Mg-lidocaine cardioplegia group. These data suggest that Mg-lidocaine-1-aspartate solution is superior to GIK solution as a cardioplegic solution, and that such will feasibly provide myocardial protection for 2 hours of hypothermic cardiac arrest, in an experimental reperfused model.

Electrolyte versus blood cardioplegia: randomized clinical and myocardial ultrastructural study

In 40 consecutive patients undergoing coronary artery bypass, one of two solutions for cardioplegia, each containing 30 mEq/L of K+ was used randomly. The groups were comparable except for intramyocardial temperature. With electrolyte solution (Group A), it was 16.5 degrees +/- 0.34 degrees C, while with blood from the pump-oxygenator (Group B) it was 20.3 degrees +/- 0.41 degrees C (p less than 0.001). After bypass left atrial pressure (LAP) was 11.9 +/- 0.67 torr in Group A and 8.1 +/- 0.49 torr in Group B (p less than 0.001). CPK-MB was elevated in 45% of Group A patients versus 15% in Group B (p less than 0.05). No patient died. Two myocardial infarctions occurred in Group A and one in Group B. Stereological morphometric electron microscopy was performed on biopsy specimens taken from the left ventricle (1) before perfusion, (2) after cardioplegia, and (3) 30 minutes after reperfusion. Group A showed marked intracellular edema, mitochondrial swelling, pronounced depletion of glycogen stores, and focal myofibrillary disorganization. Group B showed near normal myocardial ultrastructure with increased glycogen stores and minimal mitochondrial swelling. Morphometric analysis revealed a statistically significant increase in the degree of mitochondrial swelling (51%) in Group A compared with Group B after reperfusion (p less than 0.001). Thus, blood K+ cardioplegia resulted in better preservation of myocardial ultrastructure, lower ventricular filling pressure, and lesser CPK-MB release compared with this particular electrolyte cardioplegia.

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 degrees 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 greater than 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% versus 2.7% in Group 2; p less than 0.05). Biochemical analysis of the biopsies indicates that the myocardial concentration of creatine phosphate decreases by about 50% after topical cooling (p less than 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.

Isolated viable rat cardiac myocytes as a tool for evaluating histochemical methods for diagnosis of myocardial ischemia. I. Mitochondria-bound oxidoreductases--a preliminary report

A pilot study has been performed to evaluate the usefulness of isolated viable rat cardiac myocytes in the evaluation of histochemical oxidoreductase methods for estimating cellular anoxic damage. Data are presented in support of the use of succinate dehydrogenase and beta-hydroxybutyrate dehydrogenase for evaluating different degrees of cellular damage. It appears that upon anoxia biochemical signs of membrane leakage do occur earlier than positive histochemical reactions. However, trypan blue staining occurs at a later time point. Probably the histochemical reaction-rates are limited by the penetration of both the substrate and the electron acceptor, in this case nitro blue tetrazolium, into the cells and the mitochondria.

A study of the subendocardial ultrastructural changes in the volume-overloaded left ventricular hypertrophy: a comparison of the effects of aortic and mitral regurgitation

Ultrastructural changes of the subendocardial layer of the volume-overloaded left ventricle were studied in patients who underwent open heart surgery for chronic aortic valve disease (4 patients) and mitral valve disease (6 patients). Patients in these two entities were estimated to be in the same level of hemodynamic functional capacity. In aortic valve disease, the subendocardial layer of the hypertrophied left ventricle showed degeneration of cardiac muscle cells. Conversely, degeneration of cardiac muscle was rarely observed in those with mitral valve disease. Numerous small and medium sized mitochondria were observed in the subendocardial layer of the left ventricle in aortic valve and mitral valve diseases and suggested that the patients in both groups were well compensated at the time of surgery. Moderate to severe dilatation of tubules of the sarcoplasmic reticulum was observed with significantly higher incidence in the case of aortic valve disease. The hypertrophied myocardium as a result of aortic valve disease showed more ischemic damage than that due to mitral regurgitation, even with the same levels of hemodynamic functional capacity. These data suggest that the myocardium in cases of mitral regurgitation tolerates open heart surgery to a much greater extent and that the prognosis is better.