Influence of nifedipine on collateral blood flow during acute ischemia in the dog

Protective effect of collateral vessels during coronary angioplasty

To assess the potential protective role of collateral vessels 27 patients undergoing angioplasty of the left anterior descending coronary artery were studied by intravenous digital subtraction left ventriculography. Fifteen patients had no collateral vessels (group 1) and 12 had some degree of collateral supply (group 2). During balloon inflation ST segment elevation in group 1 (4.9 mm) was significantly greater than that in group 2 (0.9 mm). Similarly the reduction in left ventricular ejection fraction was significantly greater in group 1 (24%) than in group 2 (12%). Both the size of ST segment elevation and the fall in ejection fraction correlated inversely with the extent of the collateral supply (r = -0.680 and r = -0.446 respectively). During balloon occlusion of the anterior descending coronary artery the percentage shortening of the anterior and apical segments fell in both groups but apical shortening fell to a lesser extent in group 2. An additional reduction in anterobasal contraction was confined to group 1. Electrocardiographic and ventriculographic manifestations of ischaemia produced by balloon inflation during angioplasty are less pronounced when collateral vessels are present. This suggests that the collateral circulation can protect myocardium at risk of ischaemia after coronary occlusion.

Determinants of collateral filling observed during sudden controlled coronary artery occlusion in human subjects

Higher grades of collateral circulation limit the extent of myocardial ischemia observed during balloon inflation in patients with single vessel coronary disease undergoing coronary angioplasty. However, the grade of collateral filling during sudden coronary occlusion varies from patient to patient. To assess which characteristics may predict a high grade of collateral filling, baseline clinical and angiographic variables were correlated with the grade of filling during coronary occlusion in 67 patients (whose angina ranged from 1 week to 36 months in duration) undergoing left anterior descending or right coronary artery angioplasty. A second contralateral arterial catheter was used to assess the collateral filling that reached the vessel dilated before and during transient total occlusion by the angioplasty balloon. Thirty-six patients had a proximal stenotic lesion ranging in severity from 65 to 99%. On a 0 to 3 scale, mean collateral filling grade before inflation was 0.4 versus 1.8 during inflation (p = 0.001). All 19 patients with 95 to 99% stenosis had at least grade 2 collateral filling during inflation. In contrast, 18 of 21 patients with less than or equal to 80% stenosis had only grade 0 or 1 collateral filling during inflation. There were significant positive correlations between collateral grade during inflation and 1) baseline lesion severity (r = 0.76), 2) baseline collateral filling grade (r = 0.50), and 3) vessel dilated. There was no relation between collateral filling during inflation and age, gender, risk factors, duration of angina or proximal versus distal location of the lesion. Lesion severity was the only independent variable associated with collateral filling grade.(ABSTRACT TRUNCATED AT 250 WORDS)

Limitation of myocardial necrosis with verapamil during sustained coronary occlusion in the closed-chest dog

Studies were undertaken to determine whether cardioprotection afforded by verapamil could be sustained in the dog heart during permanent coronary artery occlusion. In 48 dogs a coronary artery was occluded for 24 or 48 hours using a closed-chest embolization procedure. Dogs were assigned to either untreated control or to verapamil-treated (200 micrograms/kh, intravenous bolus within 5 minutes after coronary occlusion and then 5 micrograms/kg/min as a continuous intravenous infusion for 24 or 48 hours) groups. After 24 or 48 hours of permanent coronary occlusion, tissue necrosis was evaluated using tetrazolium staining and was related to the major baseline predictors of infarct size including anatomic risk zone (radiolabeled microsphere autoradiography) and coronary collateral flow. The correlation between infarct size and subepicardial coronary collateral flow was calculated in untreated control dogs (r = -0.91 and -0.80 for 24 and 48 hour controls, respectively); analysis of covariance indicated that verapamil treatment shifted this relation downward in both the 24- and 48-hour drug treatment groups. The equation of this regression was used to calculate the size of the infarct that would have occurred in treated dogs if drug treatment had not been initiated. The ratio of observed and calculated infarct size provides a "salvage index." In conclusion, verapamil was able to limit the extent of tissue necrosis and this cardioprotection appears to be sustained during 48 hours of permanent coronary occlusion.

Total ischemic burden: effect of vasoactive agents

Treatment of the total ischemic burden is dependent on adequate documentation of both painful and painless episodes of myocardial ischemia, an understanding of the pathophysiologic mechanisms involved, and knowledge of prognosis for affected patients. Because a vasoconstrictive component appears to be an important element in the genesis of many episodes of myocardial ischemia, those vasoactive drugs that produce increased flow in the coronary circulation should be clinically useful. Nitrates and calcium blockers--especially nifedipine--have been found to be particularly valuable in this regard in both experimental and clinical trials.

Effects of nifedipine on collateral blood flow at the lateral border of the acutely ischemic myocardium

In open-chest dogs (n = 5) the effects of nifedipine (25 micrograms/kg infused over a period of 15 min) on the collateral blood flow after left anterior descending coronary artery (LAD) ligation were separated from those on heterogeneous blood supply, i.e. flow of collateral origin plus flow in non-ischemic myocardium projecting into the ischemic area. This separation was possible using a technique based on microspheres, allowing analysis of perfusion via the left anterior descending coronary artery (LAD). Secondary effects on the ischemic heart induced by the hypotensive effect of nifedipine per se were minimized by counterbalancing the blood pressure change with an intra-aortic balloon. Nifedipine increased non-ischemic myocardial blood flow in the subendocardium from 1.11 +/- 0.10 to 2.71 +/- 0.17 (p less than 0.001) and in the subepicardium from 1.12 +/- 0.08 to 3.95 +/- 0.49 (p less than 0.001) (ml/min/g, mean +/- SE). Collateral blood flow in the centre of the ischemic area was not affected by nifedipine. In the subendocardium, it was 0.12 +/- 0.05 before and 0.09 +/- 0.09 after nifedipine, and in the subepicardium, the corresponding values were 0.31 +/- 0.10 and 0.29 +/- 0.04, respectively. At the lateral ischemic border, the nifedipine-induced increase in myocardial blood flow was only directed to the admixed normal tissue. When the blood flow was corrected for this overlapping non-ischemic tissue, no significant effect of nifedipine was measurable in the subendocardial blood flow, which was 0.12 +/- 0.03 before and 0.18 +/- 0.04 ml/min/g after drug administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Efficacy and safety of nicardipine for chronic, stable angina pectoris: a multicenter randomized trial

Nicardipine, a new calcium channel blocking drug of the dihydropyridine family, was administered to 63 patients at a dose of 30 or 40 mg 3 times daily in a multicenter, randomized, double-blind, placebo-controlled, crossover trial. Nicardipine midly increased heart rate (HR) at rest and midly decreased the blood pressure (BP) at rest. When generally similar responses to the 30- and 40-mg doses were averaged, nicardipine produced a 7% increase in peak exercise HR, which was balanced by a 6% decrease in peak exercise BP. Thus, no change occurred in the exercise HR-BP product. With nicardipine, treadmill exercise duration increased 9%, time to angina increased 15%, time to 1-mm ST-segment depression increased 16%, and oxygen consumption at peak exercise increased 13%. Mean anginal frequency declined, as did mean weekly sublingual nitroglycerin consumption, but not significantly. There were more cardiovascular side effects with nicardipine than with placebo, with at least 3 patients having increased angina judged by investigators as probably related to the drug. Vasodilatory side effects were also more frequent with nicardipine, but were generally mild and well tolerated; the drug had to be discontinued in only 1 patient, because of vasodilatory effects. Nicardipine is effective and generally well tolerated in patients with chronic stable angina.

Limitation of myocardial ischemia by collateral circulation during sudden controlled coronary artery occlusion in human subjects: a prospective study

We have shown improvement in collateral filling immediately after sudden controlled coronary occlusion in human subjects undergoing elective coronary angioplasty. It has been suggested but not proved that collateral circulation can limit myocardial ischemia. We prospectively studied 23 patients with isolated left anterior descending (n = 14) or right coronary (n = 9) disease and normal left ventriculograms during elective coronary angioplasty. A second arterial catheter was used for injection of the contralateral artery to assess collateral filling before balloon placement and during coronary occlusion by balloon inflation. Left ventriculography was performed during another inflation. Grading of collateral filling was as follows: 0 = none, 1 = filling of side branches only, 2 = partial filling of the epicardial segment, 3 = complete filling of the epicardial segment. Indexes of myocardial ischemia included percent of the left ventricular perimeter showing new hypocontractility and the sum of ST segment elevation measured on a simultaneous 12-lead electrocardiogram recorded during each inflation. Collateral filling during balloon occlusion and indexes of ischemia were assessed at 30 to 40 sec into inflation. Aortic pressure and heart rate did not correlate with the percent hypocontractile perimeter nor the sum of ST segment elevation. There was a significant correlation between the grade of collateral filling during inflation and both percent hypocontractile perimeter (r = -.85) and the sum of ST segment elevation (r = -.87). Anginal pain occurred in all patients with grade 0 or 1 collateral filling but in only 36% of patients with grade 2 or 3 collaterals. In conclusion, collateral circulation limits myocardial ischemia as assessed by the extent of new ventricular asynergy and electrocardiographic changes during coronary occlusion in patients.

Disparity of reperfusion arrhythmias after reversible myocardial ischemia in open chest and conscious dogs

Myocardial reperfusion after brief, reversible ischemia is frequently associated with malignant arrhythmias in experimental animals. These observations have been extrapolated to humans despite being restricted to anesthetized, open chest preparations. No data are available regarding the incidence of reperfusion arrhythmias after reversible (less than 20 minutes) ischemia in the conscious state. Thus, reperfusion arrhythmias after a 15 minute occlusion of the left anterior descending coronary artery were compared in 24 open chest dogs (17 anesthetized with pentobarbital and 7 with chloralose plus urethane) and 25 conscious, unsedated, trained dogs. The incidence of all rhythm disorders (single premature ventricular complexes, pairs, ventricular tachycardia and fibrillation) was markedly and significantly lower in conscious than in either pentobarbital- or chloralose-anesthetized dogs. The disparity was not accounted for by differences in coronary collateral flow, coronary reactive hyperemia or occluded bed size. The conscious animals, however, exhibited lower heart rates and arterial pressures during reperfusion than did the open chest dogs, suggesting a lower level of adrenergic stimulation, which might have contributed to the reduced incidence of reperfusion arrhythmias. Coronary reperfusion after 15 minutes of occlusion is unlikely to precipitate ventricular tachyarrhythmias in the conscious, trained dog, even after severe ischemia. The occurrence of these rhythm disorders in anesthetized models may reflect the influence of surgical trauma or excessive adrenergic activity, or both. Reperfusion arrhythmias after reversible ischemia may be considerably less common in the clinical setting than previously postulated on the basis of open chest animal experiments.

Relation between left ventricular global and regional function and extent of myocardial ischemia in the canine heart

To develop a quantitative relation between the overall severity of acute ischemia and left ventricular global and regional function, two minor axis internal diameters and myocardial wall thickness were determined using ultrasonic crystals in 10 open chest dogs with carotid-left anterior descending artery cannulation. The overall extent of ischemia produced by graded stenosis of the cannulation system was estimated by total myocardial blood flow deficit, calculated using radioactive microspheres and a balloon-reservoir perfusion technique permitting precise separation of ischemic from nonischemic tissue. Although cardiac output and left ventricular stroke work were maintained through chamber enlargement until total myocardial blood flow deficit was about 10%, ejection indexes of left ventricular function decreased progressively with increasing ischemia and correlated inversely with total myocardial blood flow deficit (r = -0.55 to -0.73). Ejection indexes of left ventricular global function correlated directly with regional function in the ischemic zone (r = 0.67 to 0.83), although global function decreased at a far slower rate than regional contraction during progressive coronary stenosis with an ischemic region comprising about 25% of total left ventricular weight. During myocardial ischemia, regional dysfunction resulted in progressive global contractile dysfunction; left ventricular hemodynamic status was maintained until ischemia was severe.

Nicardipine for stable angina pectoris

Nicardipine, 30 and 40 mg thrice daily, was administered to 66 patients with stable angina pectoris in a multicentre, randomised, double-blind, cross-over trial. With nicardipine therapy, duration of exercise and cumulative oxygen consumption increased, while times to onset of angina and 1 mm ST segment depression were prolonged. Anginal frequency and nitroglycerin consumption declined with use of nicardipine, but this did not reach statistical significance. Resting heart rate increased slightly and resting blood pressure decreased. Two patients on nicardipine and one on placebo sustained acute infarction. Otherwise, side effects were generally mild and transient.