Can unstable angina pectoris be due to increased coronary vasomotor tone?

Response of coronary arteries to nitrates, the EDRF-donor SIN-1, and calcium antagonists

Intracoronary drug administration is an important tool to study coronary effects without interaction of systemic effects. The difficult methodological aspects and the results of clinical trials in which the effects of vasodilating drugs were evaluated with respect to coronary dilatation are reviewed. Major (coronary substrate, study design) and minor (measuring devices, methods of evaluation) methodological problems make it difficult to precisely evaluate pharmacological effects such as dose-response relationship, duration of action, and selective responses, and to compare the effects of different drugs. From a clinical point of view, knowledge of the maximal effect (EDmax) in coronary stenoses and the duration of action is essential. NO-donors tend to act stronger than CA-channel blockers which may be attributable to their different modes of action. Among those NO-donors investigated, SIN-1 showed stronger effects than nitroglycerin. Only with SIN-1 were maximal effects obviously achieved. The additional administration of nitroglycerin or nisoldipine never led to a more prominent dilatation. In coronary stenoses, the underlying morphology causes a wider range of responses than is seen in normal segments: deendothelialized stenoses with high coronary tone show a larger dilatation, while fully sclerotic stenoses may not react.

Coronary vasodilatory action after nicorandil: a quantitative angiographic study

Vasodilatory effects of nicorandil on major coronary arteries were investigated in 22 patients undergoing cardiac catheterization. Nicorandil, 20 mg, was administered sublingually to 11 consecutive patients and 40 mg to 11 others. Systemic blood pressure decreased significantly without affecting the heart rate. A total of 103 selected coronary artery segments, including 17 stenotic segments, were analyzed quantitatively using a computer-assisted coronary angiographic analysis system. After administration of 20 or 40 mg of nicorandil, a significant increase of the mean diameter was observed in the proximal (+9% and +7%), midportion (+10% and +11%) and distal (+15% and +13%) parts of the left anterior descending coronary artery. Corresponding values for the proximal (+13% and +10%) and distal (+10% and +15%) segments of the circumflex artery were observed. An increase in the obstruction diameter was also observed in all but 3 of the analyzed stenotic segments. The results demonstrate that nicorandil, in the route and doses used, causes significant vasodilatation in the normal epicardial coronary segments as well as in most of the stenotic segments.

Initial and late results of coronary angioplasty for early postinfarction unstable angina

Unstable angina that occurs in the early postinfarction period is associated with an increased incidence of unfavorable cardiac events despite aggressive medical therapy. We examined the results of coronary angioplasty in 47 consecutive patients with postinfarction unstable angina who were referred for the procedure 12.9 +/- 7 days following myocardial infarction, 14 of which were Q wave and 33 of which were non-Q-wave. Coronary angioplasty was performed on a total of 55 arteries with a mean predilatation stenosis of 95 +/- 8%. These included 46 infarct-related arteries and nine noninfarct arteries. Double-vessel angioplasty was performed in eight patients. Successful coronary angioplasty (greater than 30% reduction of predilatation stenosis) was achieved in 43 patients (91%), with a mean residual stenosis of 33 +/- 28%. There was one in-hospital death, one patient required emergency bypass surgery, and two patients had early reocclusion resulting in myocardial infarctions. The 39 patients who had successful angioplasty procedures and who were discharged from the hospital without an unfavorable outcome were followed for 16.3 +/- 7 months, and repeat coronary angioplasty was required in five patients from 45 to 105 days after the initial procedure. Two patients had subsequent elective bypass surgery, one had a recurrent myocardial infarction, and one patient had a noncardiac death. For selected patients with suitable coronary anatomy, coronary angioplasty appears to offer an efficacious therapeutic option for early postinfarction unstable angina.

Calcium antagonists for Prinzmetal's variant angina, unstable angina and silent myocardial ischemia: therapeutic tool and probe for identification of pathophysiologic mechanisms

The calcium antagonists provide a unique tool to reduce myocardial oxygen demand and prevent increases in coronary vasomotor tone. For patients with Prinzmetal's variant angina, diltiazem, nifedipine and verapamil are extremely effective in preventing episodes of coronary vasospasm and symptoms of ischemia. Unstable angina pectoris is a more complex pathophysiologic syndrome with episodes of ischemia due to increases in coronary vasomotor tone, intermittent platelet aggregation or alterations in the underlying atherosclerotic plaque. Each of the calcium antagonists is effective as monotherapy in decreasing the frequency of angina at rest. Nifedipine is the only calcium antagonist that has been studied in a combination regimen with beta blockers and nitrates for patients with unstable angina, and control of angina is better with the combination regimen than with either form of therapy alone. Although symptoms of myocardial ischemia in unstable angina are reduced by calcium antagonists, these agents do not seem to decrease the incidence of adverse outcomes. Antiplatelet therapy appears to improve morbidity and mortality in patients with unstable angina, suggesting that thrombus formation may play a central role in that disorder. Episodes of silent or asymptomatic myocardial ischemia, identified by ST-segment monitoring, occur in a variety of disorders of coronary disease. Among patients with Prinzmetal's variant angina and unstable angina, episodes of silent ischemia appear to be as frequent as episodes of angina and the calcium antagonists are effective in decreasing episodes of ischemia regardless of the presence or absence of symptoms. Persisting episodes of silent ischemia among patients with unstable angina despite maximal medical therapy identify patients at high risk for an early unfavorable outcome. Among patients with stable exertional angina, episodes of silent ischemia may be up to 5 times as frequent as episodes of angina, and may be due to increases in coronary vasomotor tone, transient platelet aggregation or increases in myocardial oxygen demand. Preliminary experience suggests that calcium antagonists and beta blockers are effective in decreasing episodes of silent ischemia in patients with stable exertional angina and that a combination regimen may be more effective than either form of therapy alone.

The haemodynamic effects of nifedipine, verapamil and diltiazem in patients with coronary artery disease. A review

Of the 3 most widely used calcium antagonists--nifedipine, verapamil and diltiazem--nifedipine is the most potent arterial vasodilator. Increases in cardiac output and coronary blood flow following nifedipine administration result in part from the afterload reduction. Reflex adrenergic stimulation produces an increase in heart rate and masks a direct inhibitory effect on myocardial contractility. The negative inotropic action of nifedipine is observed during intracoronary administration or may be made apparent by concurrent beta-blocker therapy. While verapamil is also a potent vasodilator, negative inotropic and dromotropic properties are more apparent in therapeutically used dosages. Reflex sympathetic activation is also triggered by verapamil, with an offsetting of the negative inotropic effects such that little change in cardiac output results. A decrease in myocardial oxygen consumption, with or without a decrease in coronary sinus blood flow, has regularly been observed following verapamil administration. Reduced oxygen demand appears to be a major mechanism of its antianginal effect. The heart rate X systolic pressure product is decreased both by the fall in arterial pressure and, particularly after oral administration, by a decrease in heart rate. Diltiazem produces similar haemodynamic and electrophysiological effects to those of verapamil but has less potency in inducing arterial dilatation and more of a tendency to slow the heart rate. Diltiazem does not appear to cause significant increases in coronary blood flow or bring about improvement in ejectional and isovolumic indices of myocardial contraction - evidence of its intrinsic negative inotropic effect.

Effects of nifedipine on left ventricular performance in unstable angina pectoris during a follow-up of 48 hours

In 1981, a large, double-blind, randomized, multicenter trial was started in The Netherlands to evaluate the therapeutic effects of nifedipine or metoprolol in patients with unstable angina. This study, called the Holland Interuniversity Nifedipine Trial (HINT), included several hundred patients to establish potential therapeutic effects. From December 1982 until January 1984 the effects of nifedipine on left ventricular (LV) performance in a subgroup of 37 HINT patients were studied using radionuclide techniques. All patients (18 treated with nifedipine, 19 with placebo) underwent radionuclide angiography and 33 underwent thallium-201 scintigraphy just before and 48 hours after the start of treatment with the experimental medication. Radionuclide angiographic studies were also performed 1 hour (29 patients) and 4 hours (31 patients) after the start of treatment. The thallium-201 images showed defects in 24 (73%) of the baseline images and in 21 (64%) of the 48-hour images. No significant differences were seen between patients receiving nifedipine or placebo in the incidence of new defects or in the disappearance of defects at 48 hours. Changes in thallium-201 images were not related to recurrence of myocardial ischemia or the development of acute myocardial infarction. Nineteen of the 37 patients (51%) with baseline blood pool images had a reduced LV ejection fraction (EF) (38 +/- 10%) and 18 patients (49%) had a normal LVEF of 56 +/- 5%. LVEF improved after 48 hours in 8 patients receiving nifedipine and in only 1 patient receiving placebo (p less than 0.02). This effect was not present at 1 and 4 hours after treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Emergency coronary angioplasty in refractory unstable angina

We performed percutaneous transluminal coronary angioplasty as an emergency procedure in 60 patients with unstable angina pectoris that was refractory to treatment with maximally tolerated doses of beta-blockers, calcium antagonists, and intravenous nitroglycerin. The initial success rate for angioplasty was 93 per cent (56 patients). There were no deaths related to the procedure, although total occlusion occurred in four patients. Despite emergency bypass grafting, all four sustained a myocardial infarction. All the patients were followed for at least six months. Late cardiac death occurred in one patient, whereas eight had recurrent angina pectoris. There was no progression to myocardial infarction. The restenosis rate was 28 per cent (13 of 46) in the patients with initially successful coronary angioplasty who had repeat angiography. Improved cardiac functional status after sustained successful coronary angioplasty was demonstrated by an almost normal capacity on bicycle exercise testing and the absence of ischemia during thallium isotope studies in 80 per cent. We conclude that emergency percutaneous transluminal coronary angioplasty may be useful for the treatment of selected patients with unstable angina pectoris who are unresponsive to intensive pharmacologic treatment.

No adverse effects from high doses of felodipine to patients with coronary heart disease

Although vasodilators may be of value in treating hypertension and heart failure, excessive vasodilation may worsen poststenotic myocardial perfusion in patients with coronary artery disease. In this study, 11 patients with ischemic heart disease were given 0.010, 0.015, and 0.025 mg/min of felodipine, a potent arteriolar dilator, and hemodynamics and myocardial lactate extraction were measured. Plasma concentrations at the three dose levels (D1, D2, and D3) were 11 +/- 4, 22 +/- 5, and 40 +/- 8 nmol/l, respectively. Mean heart rate rose from 61 +/- 13 to 79 +/- 10 beats/min at D3 (p less than 0.01) and mean arterial pressure was reduced from 113 +/- 25 to 86 +/- 13 mmHg (p less than 0.01). There was a marked increase in cardiac index at all three dose levels (p less than 0.05 to p less than 0.01). The systemic vascular resistance was reduced by 47% at D3 and coronary vascular resistance by 44% (both p less than 0.01). Myocardial oxygen consumption was not changed by felodipine. There were three patients with myocardial lactate production both before and after drug administration, but there were no ST-segment shifts or chest pain in any patient. In conclusion, felodipine seems to be a potent vasodilator and deterioration of myocardial metabolic function occurs infrequently. Our results suggest that felodipine can be safely administered even in high doses to patients with severe coronary artery diseases.

Quantitative angiography of the left anterior descending coronary artery: correlations with pressure gradient and results of exercise thallium scintigraphy

To evaluate, during cardiac catheterization, what constitutes a physiologically significant obstruction to blood flow in the human coronary system, computer-based quantitative analysis of coronary angiograms was performed on the angiograms of 31 patients with isolated disease of the proximal left anterior descending coronary artery. The angiographic severity of stenosis was compared with the transstenotic pressure gradient measured with the dilation catheter during angioplasty and with the results of exercise thallium scintigraphy. A curvilinear relationship was found between the pressure gradient across the stenosis (normalized for the mean aortic pressure) and the residual minimal area of obstruction (after subtracting the area of the angioplasty catheter). This relationship was best fitted by the equation: normalized mean pressure gradient = a + b . log [obstruction area], r = .74. The measurements of the percent area of stenosis (cutoff 80%) and of the transstenotic pressure gradient (cutoff 0.30) obtained at rest correctly predicted the occurrence of thallium perfusion defects induced by exercise in 83% of the patients.

Blockade of coronary reactions to arachidonic acid by glyceryl trinitrate and tranylcypromine

Isolated perfused hearts of rats or guinea pigs reacted to bolus doses of arachidonic acid (AA) with a coronary constriction followed by a protracted vasodilatation phase. Glyceryl trinitrate (GTN; 55-95 microM) produced coronary dilatation during which the AA-induced constriction remained unaltered, or even enhanced. After 'acute tolerance' developed by sustained GTN infusion, the constrictor phase of AA was inhibited while the vasodilatation continued unaltered or slightly enhanced. Nitroprusside (Np; 5-56 microM) determined a coronary vasodilatation that persisted throughout its administration and appeared to be associated with an inhibition of the AA-induced coronary constriction. While withdrawal of Np resulted in an immediate recovery of coronary flow levels and of the reactions to AA, the blockade of AA-coronary constriction continued after GTN withdrawal. Tranylcypromine (TRC) infusion did not alter the basal coronary flow, but it produced a specific inhibition of the AA-induced coronary vasodilatation. We postulated that the blockade of the coronary constriction exerted during GTN acute tolerance would result from an inhibition of the synthesis of a constrictor metabolite (thromboxane-like substance?) formed in the coronaries through the cyclooxygenase metabolic pathway of AA.

Intracoronary infusion of small doses of nifedipine lowers regional myocardial O2-consumption without altering regional myocardial function

Intracoronary infusion of low doses (0.1-0.3 microgram X kg-1) of nifedipine caused dose-dependent decreases in regional myocardial O2-consumption, without significant changes in any of its major global hemodynamic determinants: heart rate, left ventricular systolic and end-diastolic pressure and maxLVdP/dt. Furthermore, regional myocardial function was unaltered. It is suggested that nifedipine decreased myocardial O2-consumption by a direct effect on myocardial metabolism. Some of the possible mechanisms involved are discussed.