Acceleration of recovery of mitochondrial function after coronary reperfusion by various coronary dilating drugs in canine hearts

Nicardipine or nitroglycerin in patients with failed percutaneous coronary angioplasty: effect on myocardial diastolic function

OBJECTIVE

To evaluate whether intracoronary vasodilators can improve diastolic function in 32 patients with failed percutaneous transluminal coronary angioplasty (PTCA).

DESIGN

Clinical trial.

SETTING

Single-institution, academic hospital.

PARTICIPANTS

Failed PTCA patients undergoing emergency coronary artery bypass grafting surgery.

INTERVENTIONS

Patients were divided into 2 groups: group A received 0.1 mg of intracoronary nicardipine, and group B received 20 microg of intracoronary nitroglycerin. Both drugs were administrated via a coronary dilatation perfusion catheter inserted in the catheterization laboratory by the cardiologist. Subsequently, they were continuously infused via the side port of the introducer of the pulmonary artery catheter and titrated to keep systolic blood pressure at about two thirds of the control value. Transesophageal echocardiography (Power Vision/6000, 9-mm 5MHZ Probe; Toshiba, Elmsford, NY) was used in this study.

MEASUREMENTS AND MAIN RESULTS

Left ventricular ejection fraction, cardiac index, tissue Doppler imaging velocity of the left ventricle and mitral annulus, and troponin levels were measured before and after administration of the 2 vasodilators and after cardiopulmonary bypass. Diastolic dysfunction was found preoperatively in all the patients and responded only to intracoronary nicardipine. Ea of mitral annulus velocity significantly increased in group A patients from 7.5 +/- 0.02 to 11.8 +/- 0.01 (p < 0.005) and decreased in group B patients from 8.0 +/- 0.03 to 7.5 +/- 0.02 after nicardipine or nitroglycerin administration. Left ventricular ejection fraction and cardiac index increased significantly (p < 0.005) only after nicardipine administration. Troponin levels were significantly lower in group A than in group B patients (p < 0.005).

CONCLUSION

Intracoronary nicardipine improves diastolic function and myocardial flow velocity in patients with failed PTCA undergoing emergency coronary artery bypass graft surgery.

Haemodynamic and energetic properties of stunned myocardium in rabbit hearts

OBJECTIVE

To amplify the description of myocardial stunning.

DESIGN

Control versus 30 min after a 20 min no flow ischaemia.

EXPERIMENTAL ANIMALS

15 isolated rabbit hearts perfused with erythrocyte suspension.

MAIN OUTCOME MEASURES

Left ventricular systolic function in terms of aortic flow, peak systolic pressure (LVPmax), dP/dtmax, and the end systolic pressure-volume relation (ESPVR); early relaxation from dP/dtmin and rate of left ventricular pressure decay (tau). Passive properties: ventricular and myocardial stiffness. Coronary resistance from coronary blood flow and perfusion pressure. Total myocardial oxygen consumption (MVo2tot). Total mechanical energy via pressure-volume area (PVA). Contractile efficiency (Econ) and MVo2 of the unloaded contracting heart (MVo2unl). External mechanical efficiency (Eext) from stroke work and MVo2tot.

RESULTS

Systolic variables in stunned myocardium were significantly decreased (mean (SD)): aortic flow: 38 (13) v 9 (11) ml/min; LVPmax: 112 (19) v 74 (18) mm Hg; dP/dtmax: 1475 (400) v 1075 (275) mm Hg/s. ESPVR was not significantly decreased, at 138 (73) v 125 (58) mm Hg/ml, but the volume axis intercept was shifted rightward: 0.30 (0.37) v 0.65 (0.25) ml. Likewise, early relaxation was impaired: dP/dtmin (-1275 (250) v -975 (250) mm Hg/s) and tau (37 (7) v 46 (10) ms). LVPed was significantly decreased at 19 (12) v 12 (7) mm Hg, and both the ventricular (end diastolic pressure-volume relation) and the myocardial stiffness (constant k) were increased by 75% and 31%, respectively. Coronary resistance increased non-significantly from 0.83 (0.31) to 1.04 (0.41) mm Hg/(ml/min/100 g). Decreases in PVA (570 (280) v 270 (200) mm Hg.ml/100 g), MVo2tot (40 (9) v 34 (8) microliters/beat/100 g), and MVo2unl (26 (9) v 22 (6) microliters/beat/100 g) did not reach significance, in contrast to significant decreases in Econ (31 (18) v 14 (7)%) and Eext (0.75 (0.29) v 0.18 (0.25) arbitrary units).

CONCLUSIONS

Ventricular systolic function is decreased after brief episodes of ischaemia. The decrease in diastolic function probably amplifies the systolic deterioration during myocardial stunning. Passive diastolic properties are also changed, shown by increases in both ventricular and myocardial stiffness. The increase in coronary resistance indicates stunning at the vascular level which could limit oxygen supply. With maintained MVo2tot during stunning, external efficiency is decreased. Possible candidates for this metabolic stunning are inadequate excitation-contraction coupling and disturbed O2 utilisation by the contractile apparatus.

Electrophysiologic effects of potassium channel openers

Potassium-channel openers or activators have been introduced as a new class of antihypertensive and antianginal agents that act by increasing membrane conductance to potassium, mainly through augmentation of the ATP-sensitive potassium current. Recent in vitro studies have shown that K(+)-channel openers exert concentration-dependent effects on cardiac electrophysiology. A shortening of the cardiac action potential by acceleration of repolarization has been reported in multicellular preparations as well as in isolated myocytes. However, drug concentrations that affect the action potential duration of myocardial cells are considerably higher (10- to 100-fold) than those needed for effects on vascular smooth muscle cells. Studies in which mostly high concentrations of K(+)-channel openers were used have demonstrated that these drugs may accelerate automaticity and may promote reentrant activity. Particular interest has focused on the question whether opening of potassium channels may be potentially arrhythmogenic in the setting of acute myocardial ischemia. On the other hand, recent studies have shown that K(+)-channel openers are effective in suppressing polymorphic ventricular tachyarrhythmias induced by early afterdepolarizations and triggered activity in vivo. The clinical relevance of these experimental studies to the clinical situation is still unclear. Some K(+)-channel openers have been shown to produce electrocardiographic T-wave changes in patients in whom their effectiveness as antihypertensives was tested. However, this effect was not associated with adverse effects and has not been demonstrated for all compounds.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of prostaglandin E1 on the recovery of ischemia-induced liver mitochondrial dysfunction in rats with cirrhosis

Interruption of hepatic blood supply for 60 min deteriorated liver mitochondrial respiratory functional indices--that is, respiratory control index (RCI) and the rate of oxygen consumption in state-III respiration (ST III O2). Recovery of ischemia-induced decreases in these functional indices in a saline-administered cirrhotic liver group was retarded compared with that in a normal liver group, and significantly low RCI and ST III O2 persisted 15 min after reperfusion. Prostaglandin E1 (PGE1) did not improve ischemia-induced decreases in RCI and ST III O2 but accelerated the recovery of mitochondrial respiratory function after reperfusion. Adenosine triphosphate (ATP) levels were markedly decreased during ischemia, and retardation of ATP recovery was also observed in rats with cirrhosis. PGE1 improved the recovery of ATP level in rats with cirrhosis. Liver blood flow in the cirrhotic liver was significantly lower than that of the normal liver. PGE1 enhanced liver blood flow. These results indicate that retardation of the recovery of RCI and ST III O2 in the cirrhotic liver might be based on the decrease in tissue blood flow and that agents increasing tissue blood flow might contribute to the acceleration of the recovery of mitochondrial respiratory function.

Protection of regional mechanics and mitochondrial oxidative phosphorylation by amlodipine in transiently ischemic myocardium

The effects of amlodipine (0.3 mg/kg administered intravenously, n = 5) and placebo (n = 5) on recovery of myocardial function and respiration of isolated mitochondria were examined in "stunned" myocardium of normotensive pentobarbital-anesthetized dogs. Measures of myocardial wall motion, using sonomicrometers, and tissue blood flow, by radioactive microspheres, were obtained at baseline, 15 minutes after administration of amlodipine or placebo, after 10 minutes of left circumflex artery ligation and at 60 minutes of reperfusion. Mean aortic pressure decreased from 115 +/- 6 to 101 +/- 5 mm Hg after administration of amlodipine and remained decreased throughout the experiment. Heart rate was not significantly affected at any time. Both groups showed similar degrees of ischemia: elevation of ST segment to 4.7 +/- 1.4 vs 6.2 +/- 1.9 mV; reduction of ischemic zone shortening fraction to 0.6 +/- 1.9 vs -3.4 +/- 2.7%; and reduction of epicardial and endocardial blood flows (epicardial = 40 +/- 13 vs 43 +/- 13 ml/100 g/min; endocardial = 7 +/- 4 vs 13 +/- 6 ml/100 g/min [values for amlodipine vs placebo]). Mitochondrial state 3 rate of respiration and respiratory control index indicative of rate of adenosine triphosphate synthesis and membrane integrity in myocardial samples taken after 10 minutes of ischemia were significantly reduced in the placebo but not in the amlodipine group. Myocardial function showed significantly greater improvement in amlodipine vs placebo at 60 minutes of reperfusion as indicated by shortening fraction (17.7 +/- -1.4 vs 5.8 +/- -3.5%, amlodipine vs placebo), which may have been related to increased myocardial blood flow and decreased blood pressure during reperfusion. Thus, amlodipine pretreatment prevented mitochondrial dysfunction during ischemia and accelerated recovery of both myocardial mechanical function and blood flow when compared with placebo.