Effects of nitroglycerin on regional myocardial blood flow in coronary artery disease

Vasodilator Therapy: Nitrates and Nicorandil

Nitrates have been used to treat symptoms of chronic stable angina for over 135 years. These drugs are known to activate nitric oxide (NO)-cyclic guanosine-3',-5'-monophasphate (cGMP) signaling pathways underlying vascular smooth muscle cell relaxation, albeit many questions relating to how nitrates work at the cellular level remain unanswered. Physiologically, the anti-angina effects of nitrates are mostly due to peripheral venous dilatation leading to reduction in preload and therefore left ventricular wall stress, and, to a lesser extent, epicardial coronary artery dilatation and lowering of systemic blood pressure. By counteracting ischemic mechanisms, short-acting nitrates offer rapid relief following an angina attack. Long-acting nitrates, used commonly for angina prophylaxis are recommended second-line, after beta-blockers and calcium channel antagonists. Nicorandil is a balanced vasodilator that acts as both NO donor and arterial K(+) ATP channel opener. Nicorandil might also exhibit cardioprotective properties via mitochondrial ischemic preconditioning. While nitrates and nicorandil are effective pharmacological agents for prevention of angina symptoms, when prescribing these drugs it is important to consider that unwanted and poorly tolerated hemodynamic side-effects such as headache and orthostatic hypotension can often occur owing to systemic vasodilatation. It is also necessary to ensure that a dosing regime is followed that avoids nitrate tolerance, which not only results in loss of drug efficacy, but might also cause endothelial dysfunction and increase long-term cardiovascular risk. Here we provide an update on the pharmacological management of chronic stable angina using nitrates and nicorandil.

Role of short-acting nitroglycerin in the management of ischemic heart disease

Nitroglycerin is the oldest and most commonly prescribed short-acting anti-anginal agent; however, despite its long history of therapeutic usage, patient and health care provider education regarding the clinical benefits of the short-acting formulations in patients with angina remains under-appreciated. Nitrates predominantly induce vasodilation in large capacitance blood vessels, increase epicardial coronary arterial diameter and coronary collateral blood flow, and impair platelet aggregation. The potential for the prophylactic effect of short-acting nitrates remains an under-appreciated part of optimal medical therapy to reduce angina and decrease myocardial ischemia, thereby enhancing the quality of life. Short-acting nitroglycerin, administered either as a sublingual tablet or spray, can complement anti-anginal therapy as part of optimal medical therapy in patients with refractory and recurrent angina either with or without myocardial revascularization, and is most commonly used to provide rapid therapeutic relief of acute recurrent angina attacks. When administered prophylactically, both formulations increase angina-free walking time on treadmill testing, abolish or delay ST segment depression, and increase exercise tolerance. The sublingual spray formulation provides several clinical advantages compared to tablet formulations, including a lower incidence of headache and superiority to the sublingual tablet in terms of therapeutic action and time to onset, while the magnitude and duration of vasodilatory action appears to be comparable. Furthermore, the sublingual spray formulation may be advantageous to tablet preparations in patients with dry mouth. This review discusses the efficacy and utility of short-acting nitroglycerin (sublingual spray and tablet) therapy for both preventing and aborting an acute angina attack, thereby leading to an improved quality of life.

Intravenous vasodilator therapy in congestive heart failure

The prevalence of congestive heart failure (CHF) is increasing in the US and worldwide, partly because patients are living longer. Treatment of CHF is mostly on an outpatient basis, but inpatient care is required for decompensated CHF, acute CHF or poor response to outpatient treatment. Control of symptoms is usually achieved by diuresis. Intravenous (IV) vasodilators are an important adjunct to the inpatient treatment of CHF. They work mainly by reducing the afterload on the myocardium although preload reduction also occurs. After clinical stabilisation, the goal is to switch to a maintenance oral regimen to be continued as outpatient therapy. The range of IV vasodilators available for inpatient treatment of CHF includes nitrates, phosphodiesterase inhibitors, dobutamine, morphine, ACE inhibitors, B-type natriuretic peptides and endothelin receptor antagonists. As each agent may have a different mechanism or site of action, each agent may affect preload, contractility or afterload to a different extent and it may be desirable to choose one over the other in a particular clinical setting. Examples of standard therapy include dobutamine, milrinone and nitroglycerin. Nesiritide, a B-type natriuretic peptide, is a newer vasodilator and US FDA approved for use in acute CHF. However, most studies with this agent have been in small numbers of patients with anecdotal findings. Larger studies are warranted to pinpoint the efficacy and adverse effects of this agent. It is primarily used to reduce the acuity of decompensated CHF on admission to hospital.Endothelin receptor antagonists show promise in the management of acute CHF, but continue to be investigational. Long-term data on their efficacy and safety are limited. None of the endothelin receptor antagonists are FDA approved for use in patients with CHF.

The non-invasive assessment of hibernating myocardium in ischaemic cardiomyopathy--a myriad of techniques

Heart failure is placing an ever-increasing burden on society. Many subjects with heart failure and underlying coronary artery disease have a significant amount of akinetic but viable myocardium that is able to contract should myocardial perfusion improve (hibernating myocardium). Non-randomised studies have shown prognostic benefit in subjects with hibernating myocardium undergoing revascularisation. Several non-invasive techniques have been developed to assess the presence or absence of hibernating myocardium. This review will examine the epidemiology and underlying pathogenesis of hibernating myocardium; evaluate the non-invasive techniques for diagnosing hibernating myocardium, and look at therapeutic intervention in subjects with hibernating myocardium.

A double-blind, randomized study of the effect of immediate intravenous nitroglycerin on the incidence of postprocedural chest pain and minor myocardial necrosis after elective coronary stenting

BACKGROUND

Anginal chest pain without creatine kinase (CK) elevation is frequently observed in the first hours after coronary stenting. Possible causes of ischemic episodes are microembolism, side branch occlusion, coronary vasospasm, and disturbances of microvascular circulation. In a prospective, double-blind, randomized trial, we tested the effect of intravenous nitroglycerin on the incidence of angina and minor myocardial necrosis (MMN), as detected by cardiac troponin I increase, after elective coronary stenting.

METHODS AND RESULTS

One hundred patients were randomly assigned to intravenous nitroglycerin (group A: n = 50, goal dose 100 microgram/min) or placebo (group B: n = 50, NaCl 0.9%) during 12 hours after stenting. Patients with acute myocardial infarction, known intolerance to nitrates, and hemodynamic instability during angioplasty were excluded. The 2 groups were comparable in respect to baseline and interventional variables, except for age (group A: 60 +/- 9 years, group B: 56 +/- 10 years; P =.04). The incidence of chest pain was not influenced by nitroglycerin (group A: 18%, group B: 22%; P = not significant). However, the occurrence of MMN was significantly reduced by nitroglycerin (group A: 5%, group B: 19%, P =.036). A rise in CK with significant CK-MB fraction was observed in only 2 patients in group B (both less than twice upper limit). Only 4 of the 10 patients with MMN also had chest pain.

CONCLUSIONS

Routine use of intravenous nitroglycerin after coronary stenting significantly reduced the occurrence of minor myocardial necrosis. However, the incidence of postprocedural chest pain remained unchanged.

High-dose nitrates in the immediate management of unstable angina: optimal dosage, route of administration, and therapeutic goals

Nitrates are commonly used for rapid relief of ischemia in the initial management of unstable angina. However, their optimal dosage, route of administration, and therapeutic goals have not been fully established. This study was conducted to determine the optimal dosage and mode of administration (intravenous bolus versus sublingual spray) of nitrates and the therapeutic goals of their use in the immediate management of unstable angina. In a single-center prospective trial, 72 consecutive patients with unstable angina accompanied by typical ST-segment depression on electrocardiogram were randomly assigned to receive isosorbide dinitrate either as repeated intravenous boluses or as sublingual sprays while being delivered to the hospital by a mobile intensive care unit. Optimal nitrate dosage was tailored to pain relief while monitoring mean blood pressure reduction to an optimal range (5% to 20%) without dosage restriction. The mean nitrate dosage needed for ischemia control during the first hour of treatment was 7.8 +/- 3.8 mg. Optimal blood pressure reduction was achieved by significantly more intravenously treated patients than sublingually treated patients (68% v 41%, P = .037). Intravenously treated patients also experienced a more pronounced therapeutic effect, as assessed by reduction in chest pain score (67% v 39%, P = .0004) and decrease in ST-segment depressions (57% v 27%, P = .004). These results show that higher doses of nitrates than previously recommended are required for ischemia control during the initial management of unstable angina. The use of repeated intravenous boluses is safe and more easily controlled and, therefore, more efficacious than sublingual sprays in inducing the maximal anti-ischemic effect while avoiding significant hypotension.

Nitroglycerin enhances the ability of dobutamine stress echocardiography to detect hibernating myocardium

BACKGROUND

A biphasic response of wall thickening with initial improvement and subsequent deterioration during dobutamine stress echocardiography (DSE) has been increasingly used for detection of hibernating myocardium. However, the improvement of wall thickening at low-dose DSE may be limited in hibernating myocardium by severe hypoperfusion. Nitroglycerin (NTG) improves myocardial perfusion, reduces oxygen demand, and may enhance low-dose dobutamine to improve wall thickening.

METHODS AND RESULTS

A pig model of myocardial hibernation of 24 hours to 7 days was created through severe left anterior descending coronary artery stenosis with coronary flow reductions of approximately 40%, producing severe regional left ventricular dysfunction but no infarction in seven pigs. Myocardial infarction was produced in five pigs with occlusion of the artery. DSE was performed with incremental doses with and without an NTG infusion of 50 to 100 microg/min. In the hibernating group, NTG alone improved wall thickening in the hibernating region modestly from 11.4+/-7.2% at baseline to 19.1+/-7.0%. The improvement was associated with increased regional coronary flow from 0.46+/-0.12 to 0.55+/-0.13 mL x beat(-1) x 100 g myocardium(-1) (P<.05). There was an additive effect of NTG to low-dose (2.5 to 5 microg x kg(-1) x min(-1)) dobutamine on wall thickening in the hibernating region. The improvement of wall thickening of hibernating myocardium with NTG and dobutamine, from 23.7+/-11.1% to 31.1+/-8.9% (P<.001), was associated with an increase in regional coronary flow (P<.01). NTG did not prevent high doses of dobutamine from inducing deterioration of wall thickening in hibernating myocardium. In the infarcted group, no improvement in wall thickening was observed in infarcted regions during NTG infusion, dobutamine infusion, or the combination.

CONCLUSIONS

NTG enhances the improvement of wall thickening at low-dose dobutamine and does not prevent high-dose dobutamine from inducing ischemia in hibernating myocardium. Thus, NTG augments the biphasic response of wall thickening and improves the accuracy of DSE for detecting viable myocardium.

Computer-aided video angiometry in isolated rabbit hearts: a new method assessing epicardial coronary selectivity

The clinical value of coronary vasodilators in antianginal therapy depends on the ratio of their epicardial versus resistance coronary vessel actions. The coronary flow measured in standard isolated heart preparations, however, does not allow any conclusion about the function of epicardial vessels. Thus, we established a new technique assessing the epicardial coronary diameter directly by video angiometry. Pictures from the cardiac surface were taken by a videocamera mounted on a long-distance microscope. The video signal was digitized for computer-aided evaluation. An area of interest (AOI) was laid over the vascular section to be measured. The gray values of the pixels across the epicardial vessel were registered, and a mean curve of distribution was obtained by averaging the gray values from all video lines within the AOI. The inner epicardial coronary diameter resulted from the distance between the points of inflection of this mean curve of distribution. Experiments with NO-vasodilators and adenosine showed that epicardial coronary arteries of isolated perfused rabbit hearts have no appreciable tone. Pretreatment of the hearts with a combination of histamine (10[-6] mol/l), cimetidine (10[-5] mol/l), and adenosine (10[-7] mol/1), however, caused a marked contraction of the conductive vessels. NO-donors selectively dilated epicardial vessels in such pretreated hearts whereas adenosine increased both epicardial coronary diameter and coronary flow, with only a slight tendency toward preferential action on resistance vessels in low concentrations. Simultaneous registration of coronary flow and epicardial coronary diameter in isolated rabbit hearts pretreated with a spasmogenic drug combination (histamine, cimetidine, and adenosine) may be a feasible method assessing epicardial selectivity of coronary vasodilators.

Regional distribution and kinetics of [18F]6-flurodopamine as a measure of cardiac sympathetic activity in humans

OBJECTIVES

To determine whether an increase in cardiac sympathetic activity produced by exercise or sublingual glyceryl trinitrate causes an increased rate of loss of fluorine-18 from the myocardium after intravenous [18F]6-fluorodopamine ([18F]F-DA) in normal volunteers. In addition, to determine the contribution of non-specific uptake of [18F]F-DA in the myocardium in patients with recent heart transplant.

PROTOCOL

[18F]F was prepared by direct electrophilic fluorination of dopamine. Nine healthy volunteers each received 1.85 x 10(8) Bq (168-250 micrograms) [18F]F-DA over a period of 3 min and were scanned for 2 h in an ECAT 953/31 tomograph. Three controls were scanned before and after vigorous cycle exercise and two were scanned before and after sublingual glyceryl trinitrate. In addition, two patients (1 and 2 years post-heart transplant) underwent a myocardial perfusion study with ammonia labelled with nitrogen-13 followed by an [18F]F-DA study.

RESULTS

There was intense uniform uptake of [18F]F-DA throughout the myocardium in the healthy volunteers. The time course of 18F in the myocardium under resting conditions fitted a biexponential function with mean half-times of 8.0 and 109 min. Vigorous exercise produced a three to fivefold increase in the rate of loss of 18F compared with that when resting. After glyceryl trinitrate, one control had a profound reduction in blood pressure (23%) and twofold increase in the rate of loss of myocardial 18F. The other control had no physiologically significant change in blood pressure, heart rate, or rate of loss of myocardial 18F. Uptake of [18F]F-DA in the two posttransplant patients was confined to a small anterobasal region adjacent to the atrioventricular groove, while blood flow, as measured with [13N] ammonia, was uniformly distributed throughout the myocardium. Partial reinnervation of the myocardium was confirmed by the presence of distinct low frequency spectral peaks of the heart rate power spectrum in both patients.

CONCLUSIONS

These results suggest that the uptake of [18F]F-DA reflects the distribution of cardiac sympathetic innervation and that the rate of loss of 18F from the myocardium partially reflects spill over of noradrenaline. The technique may be useful in investigating various cardiac conditions in which the sympathetic system is compromised.

Redistribution of myocardial blood flow with topical nitroglycerin in patients with coronary artery disease

BACKGROUND

Unlike nonselective coronary vasodilators, nitroglycerin (GTN) is said to exert its primary vasodilatory effect on epicardial conductance vessels. Thus, in experimental models of coronary occlusion GTN appears to preferentially direct blood flow to poststenotic zones of ischemia. This phenomenon has, to date, not been tested in humans. Using positron emission tomography we examined the effect of transdermal GTN on global and regional myocardial perfusion in patients with angiographically proven coronary artery disease.

METHODS AND RESULTS

Myocardial perfusion with [13N]ammonia was estimated from dynamic time-activity curves at baseline and 3 hours following application of either a 0.4 mg/h GTN skin patch (n = 10) or a placebo patch (n = 10) in a double-blind parallel design. From resliced cross-sectional images, regional flow, expressed as [13N]ammonia retention, was estimated from 216 myocardial sectors. Ischemia was defined as a significant reduction (> 2 SDs from average counts/pixel in maximally perfused zones) in [13N]ammonia retention within 10 contiguous myocardial sectors coupled with an increase or no change in counts derived from [18F]fluorodeoxyglucose. There was no change in global myocardial blood flow as expressed by [13N]ammonia retention following either placebo (0.61 +/- 0.14 to 0.62 +/- 0.12 min-1) or GTN (0.75 +/- 0.22 to 0.74 +/- 0.19 min-1). Conversely, there was a significant increase in the proportion of blood flow to the ischemic zones with GTN (73.9 +/- 12.6% to 94.9 +/- 17.8%; P < .05). No change in the distribution of blood flow to either ischemic or nonischemic zones was observed with placebo. A slight but insignificant decrease in [13N]ammonia retention in nonischemic zones was observed with GTN (1.01 +/- 0.31 to 0.93 +/- 0.26 min-1).

CONCLUSIONS

This study suggests that under resting conditions topical GTN alters myocardial perfusion by preferentially increasing flow to areas of reduced perfusion with little or no change in global myocardial perfusion in patients whose angina is responsive to GTN.

Use of nitroglycerin for the treatment of acute myocardial infarction

After a decade of warnings against the use of nitrates in acute myocardial infarction (MI), they are becoming recognized for their potential to salvage left ventricular (LV) myocardium, geometry and function. Low-dose intravenous (IV) nitroglycerin (NTG) infusion for the first 48 h after acute MI, titrated to lower mean blood pressure by 10% to 30%, but not below 80 mmHg, has been shown to be safe, to improve hemodynamics, and to decrease infarct size, infarct expansion, complications, and deaths in a prospective, randomized, single-blind study of 310 patients. In addition, low-dose NTG infusion for the first 48 h, followed by prolonged buccal NTG given during healing after acute MI in an eccentric dose schedule to minimize tolerance, was found to limit further progressive remodeling and preserve LV function. Meta-analysis of nitrate studies in acute MI indicate that they improve survival. Preliminary and ongoing studies suggest that prolonged NTG therapy post MI can produce further benefit.

Comparison of the effects of two different galenical preparations of glyceryl trinitrate on pulmonary artery pressure and on the finger pulse curve

The time course and the magnitude of the effect of glyceryl trinitrate (GTN) on central venous (pulmonary artery diastolic pressure-PAPd) and peripheral arterial (a/b-ratio of the finger pulse wave) haemodynamics were compared in a randomized double-blind cross-over study in 12 patients suffering from congestive heart failure (NYHA II-III) with elevated PAPd at rest (> or = 15 mmHg). The data were obtained in a bioavailability study of two sprays of glyceryl trinitrate, which differed in their galenical characteristics and in the dose of GTN (0.4 mg vs. 0.8 mg). Following sublingual administration of each spray, PAPd, a/b-ratio and the plasma concentrations of GTN and its metabolites were measured up to 30 min. The relative bioavailability of GTN of the test preparation was estimated to be 157%, 161% and 147%, when calculated from the plasma concentration-time data or the integrated effect of GTN on a/b-ratio or PAPd, respectively. The mean time courses of the decrease in PAPd and the increase in the a/b-ratio of the finger pulse curve were mirror images. Thus, there was a strong correlation between the mean values of PAPd and a/b-ratio following the administration of glyceryl trinitrate. Since the slope of the relationship differed considerably between the patients, the magnitude of effect of GTN on PAPd in the individual patient could not be predicted from the changes in a/b-ratio.

Functional significance of coronary collateral vessels in patients with previous 'Q' wave infarction: relation to aneurysm, left ventricular end diastolic pressure and ejection fraction

The importance of coronary collateral circulation in relation to the left ventricular function, aneurysm formation and size was investigated in 100 patients with previous 'Q' wave myocardial infarction who underwent coronary angiography. Aneurysms were present in 20% of patients. The majority of these (80%) patients had severe or total occlusion of the left anterior descending artery. Thirty four percent of patients without aneurysm had significant collaterals whereas 25% of patients with aneurysms had collaterals (P > 0.05). However, the size of the aneurysm was smaller when adequate collateral circulation was present (Collateral Index 2 or above). The incidence of hypertension and diabetes was similar in both groups. Collateral circulation was more frequently seen in the anterior (60%) as compared to inferior myocardial infarction (40%), but Collateral Index was higher in right coronary artery disease. The number of patients with an elevated left ventricular end-diastolic pressure (> 12) or poor ejection fraction was similar in the two groups with and without collaterals. Thus, there was no beneficial effect of collateral circulation on left ventricular function. The incidence of aneurysm was not significantly lower, although the size of the aneurysm was significantly smaller in the presence of collateral circulation.

Sustained beneficial effect of a seventy-two hour intravenous infusion of nitroglycerin in patients with severe chronic congestive heart failure

To determine whether a 72-hour infusion of nitroglycerin produces hemodynamic improvement in patients with severe congestive heart failure and to assess the contributing role of various possible causes of hemodynamic tolerance to nitroglycerin, 19 patients received an infusion of nitroglycerin 1.5 micrograms/kg/min for 72 hours. In a subgroup of patients (n = 10), there was an increase in stroke work index and a decrease in ventricular filling pressures throughout the infusion and even after it was discontinued. Tolerance to the hemodynamic effects of nitroglycerin was partially reversed 8 hours after the infusion was stopped. Neurohumoral changes occurred but appeared to play only a minor role in the development of nitroglycerin tolerance. However, hematocrit fell 9 +/- 5%, which suggests that an increased intravascular volume contributed to tolerance. In summary: (1) a 72-hour infusion of nitroglycerin improves ventricular function in some patients with severe heart failure; (2) volume shifts from the extravascular to the intravascular compartments may, at least in part, be responsible for nitroglycerin tolerance; and (3) reflex neurohumoral activation may also play a small role in nitrate tolerance.

Hyperosmotic mannitol and collateral blood flow to ischemic myocardium

Elevation of extracellular osmolality reduces the extent of myocardial and endothelial cell swelling that accompanies acute ischemia, and the reduction of cell swelling is associated with an increase in collateral blood flow to the ischemic area. However, little is known about the effects of hyperosmolality on the vascular resistance of the collateral coronary vasculature. We compared the effects of hyperosmolar mannitol with those of nitroglycerin and dipyridamole on the vascular resistance of large collateral coronary vessels and of the small arterial vasculature in an isolated heart model of regional ischemia. Elevation of osmolality by mannitol increased collateral blood flow to the ischemic region through at least two mechanisms. First, increasing osmolality resulted in dilation of large arterial conductance vessels, similar to that produced by nitroglycerin. In addition, mannitol produced an effect on the coronary circulation at a microvascular level which, per se or in combination with its effect on larger collateral conductance vessels, increased collateral blood flow to ischemic regions.

Intravenous labetalol for the treatment of hypertension after carotid endarterectomy

Hypertension after carotid endarterectomy has a variable incidence ranging up to 56%. Blood pressure (BP) control is essential due to possible increased risk of morbidity from neurologic deficits or cardiovascular complications. This study evaluated intravenous labetalol for control of hypertension after carotid endarterectomy. Sixty ASA II-IV patients were studied; 20 developed BP high enough for treatment with labetalol. The anesthetic technique was standardized. Labetalol was administered at the conclusion of surgery as a 20-mg bolus over two minutes followed by 40 mg every 10 minutes until the desired BP was achieved (BP less than or equal to 10% above average preoperative BP or less than 150 mmHg, systolic) or 300 mg had been given. The mean total dose of labetalol was 42.0 +/- 33.0 mg (mean +/- SD) and mean time to reach the desired BP was 16.2 +/- 21.4 minutes. Systolic, diastolic, mean arterial pressure and heart rate significantly decreased after labetalol treatment and remained so for the remainder of the 180-minute study period. There was no hypotension, bradycardia, evidence of myocardial ischemia or central nervous system dysfunction present with labetalol treatment. Blood samples were obtained for determination of plasma renin activity, epinephrine, and norepinephrine in 10 patients who developed hypertension and received labetalol, and 10 patients who did not develop hypertension. In the patients developing hypertension, there was a significant elevation in epinephrine just before treatment, that decreased by 30 minutes after treatment. Norepinephrine levels became significantly elevated five minutes after labetalol treatment in the group with hypertension and remained elevated for 120 minutes. Concomitantly, there was a significantly lower plasma renin activity seen in this group.(ABSTRACT TRUNCATED AT 250 WORDS)

Nitrates

Nitroglycerin and the long-acting nitrates are playing an increasingly important role in cardiovascular medicine. These agents are recommended in all of the various anginal syndromes and are as effective as the beta-blockers and calcium channel antagonists. There is a definite place for nitrate therapy in treating the complications of acute myocardial infarction. These drugs are also highly effective as unloading therapy in congestive heart failure. The mechanisms of action of the nitrates are reviewed in this article. Information is provided regarding nitrate efficacy in all the major clinical syndromes in which these drugs are used. Finally, appropriate dosing strategies are suggested that should eliminate the potential problem of nitrate tolerance.

Attenuation of nitroglycerin-induced coronary hyperemic blood flow in patients with left anterior descending coronary collaterals

Although intracoronary nitroglycerin (NTG) is frequently administered to patients having occluded coronary arteries undergoing invasive procedures such as percutaneous transluminal coronary angioplasty or thrombolysis, the extent of NTG-induced augmentation of myocardial blood flow in patients with collaterally filled occluded arteries is incompletely understood. To examine NTG-induced increases in coronary blood flow in patients with occluded left anterior descending coronary arteries (LAD), coronary and systemic hemodynamics were measured during bolus administration of NTG into the left coronary artery in 10 patients with normal LAD (Group 1), 11 patients with greater than 70% and less than 100% narrowing of the LAD (Group 2), and 10 patients who had total occlusion of the LAD with angiographic collateral filling and anterior ventricular wall motion abnormalities (Group 3). NTG increased anterior regional great vein flow (thermodilution) from 72 +/- 19 to 140 +/- 60 ml/min (p less than 0.05), 67 +/- 27 to 108 +/- 66 ml/min (p less than 0.05), and 59 +/- 27 to 74 +/- 36 ml/min (p = NS vs. control, p less than 0.05 vs. peak flow for Group 1) with relative increases from control of 91 +/- 41%, 56 +/- 34%, and 25 +/- 22% for the three groups, respectively. The percent change for Group 3 was significantly lower than both Groups 1 (p less than 0.01) and 2 (p less than 0.05). These data indicate that myocardial hyperemic blood flow responses to intracoronary NTG are markedly attenuated in patients with occluded but collaterally supplied vessels. During invasive procedures in these patients, although significantly attenuated, intracoronary NTG may potentially provide a beneficial effect by augmenting blood flow through collaterals or in adjacent regions.

The acute effect of sublingual nifedipine and isosorbide dinitrate on plasma viscosity in patients with acute myocardial infarction

The effect of sublingual nifedipine 10 mg (pierced capsule) and isosorbide dinitrate (ISDN) 5 mg on plasma viscosity (Pl.V) was investigated in 60 consecutive patients 7-10 days after hospitalization for acute myocardial infarction (AMI), who were randomized for either nifedipine (30 patients) or ISDN (30 patients). Pl.V, hematocrit (Htc), and erythrocyte sedimentation rate (ESR) were measured 20 minutes before and thereafter at 5, 10, and 30 min after drug administration while in the recumbent position. Blood pressure (BP) and heart rate (HR) were determined before each blood sample. In 18 patients (60%) Pl.V decreased by greater than 0.05 centipoise (Cp) after nifedipine (0.0953 +/- 0.033 Cp p less than 0.001 vs. initial values). After ISDN, Pl.V decreased by greater than 0.05 Cp (0.0933 +/- 0.036 Cp) in only 7 patients (23%). Systolic blood pressure (SBP) fell by 11.7 +/- 14.6 mmHg after nifedipine and by 16 +/- 14 mmHg after ISDN (nifedipine vs. ISDN = NS). Diastolic blood pressure (DBP) fell by 8 +/- 9.6 mmHg after ISDN and by 6.6 +/- 19.3 mmHg after nifedipine (nifedipine vs ISDN = NS). HR, ESR, and Htc did not change after drug administration. It is thus concluded from our study that nifedipine 10 mg sublingual has a significant Pl.V-lowering activity compared to sublingual ISDN 5 mg in patients with AMI.

Alterations in regional myocardial blood flow after nitroprusside and nitroglycerin in patients with and without significant coronary artery disease

To evaluate vasodilator-induced redistribution of regional myocardial blood flow, intravenous sodium nitroprusside and nitroglycerin were administered in doses producing matched reductions (15%) in mean arterial pressure at constant heart rate. Anterior left ventricular great cardiac vein blood flow (thermodilution) was measured in 14 patients without angiographic anterior collateral supply. Global coronary sinus blood flow remained constant with both nitroprusside and nitroglycerin administration, despite significant reductions in mean arterial pressure. However, nitroglycerin reduced great vein flow by 25 +/- 17% and nitroprusside by 10 +/- 16% (p less than 0.01). Subgroup analysis indicated that the nitroglycerin-nitroprusside regional blood flow differences were more pronounced in patients without significant left anterior descending coronary artery narrowing. Neither vasodilator produced significant differences in arterial-coronary sinus oxygen or lactate contents, calculated myocardial oxygen consumption, left ventricular dP/dt, or electrocardiographic or clinical signs of myocardial ischemia. Despite qualitatively similar hemodynamic effects, comparisons of vasodilator-induced relative reductions in normally supplied anterior left ventricular regional coronary blood flow suggest a mechanism of the reported beneficial effects of nitroglycerin on potentially ischemic myocardial regions.

Pharmacology of nitroglycerin and long-acting nitrates

Organic nitrates are available in a remarkably diverse variety of formulations, including sublingual, buccal and oral tablets, capsules, topical creams, ointments, patches, tapes, inhalable sprays and intravenous solutions. Although not all of these formulations are available in the United States, the array of drugs and dosages approved for use is extensive. It is only by weighing the pharmacologic properties of these agents against the patient's clinical status and needs that a concise and appropriate treatment regimen may be derived. Numerous recent studies have confirmed the protracted efficacy of the organic nitrates in the treatment of patients with angina pectoris and congestive heart failure (CHF) as evidenced by improvements in cardiac hemodynamics and desired clinical parameters. It is appropriate that the patient's dosage of nitrates be administered with a formulation most likely to be both clinically effective and well tolerated. The use of nitroglycerin and isosorbide dinitrate in the acute and chronic treatment of CHF will be discussed in the context of their unique pharmacologic and pharmacokinetic properties. A rationale for the most efficacious use of these agents will be presented. Tolerance phenomena and adverse effects (i.e., headache) will also be discussed from the perspective of their significance in chronic nitrate therapy.

Effectiveness of nicorandil in the preservation of myocardium stressed by transient ischemia and its influence on cardiac metabolism during coronary artery occlusion with subsequent reperfusion: a comparison with isosorbide dinitrate

This study was designed to investigate the effects of nicorandil in comparison to isosorbide dinitrate (ISDN) on hemodynamics, on myocardial metabolism and on effectiveness in the preservation of ischemically stressed myocardium. Repeated ischemia (3 min) was produced in anaesthetized open-chest mongrel dogs by proximal, intermittent left anterior descending artery occlusion with subsequent reperfusion. In each experiment 2--3 control occlusions were compared to 2--3 occlusions under nicorandil or ISDN. Application of both nicorandil (0.64 mumol X kg-1 body weight, i.v.) and ISDN (1.27 mumol X kg-1 body weight, i.v.) led to a significant afterload reduction and to a decrease of the coronary vascular resistance. The efficiency of the compounds in the protection of ischemic myocardium was examined by quantification of oxygen-debt and oxygen-repayment in the occlusion and reperfusion periods. Compared to control, premedication with nicorandil led to a significant increase of oxygen-debt, whereas ISDN reduced it significantly. Oxygen-repayment remained unchanged. The influence of the drugs on the metabolism of glucose, lactate and free fatty acids (FFA) was examined under basic conditions, in ischemia and during reperfusion. For all substrates, extraction, extraction ratio and oxygen extraction ratio were calculated. Under basic conditions, glucose metabolism was significantly enhanced in both groups but FFA metabolism was inhibited only by ISDN. In ischemia, FFA metabolism was enhanced by nicorandil and depressed by ISDN.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of nitroglycerin on coronary collateral flow and pressure during acute coronary occlusion

Coronary collateral function was evaluated in 21 conscious, unsedated patients by measuring aortic and distal coronary pressures and great cardiac vein flow during transient (1 minute) balloon occlusion of the anterior descending artery in the course of coronary angioplasty. Measurements were made before and during administration of intravenous nitroglycerin (NTG). Clinical, electrocardiographic and hemodynamic events of transient myocardial ischemia occurred in 10 patients before and 6 patients during NTG administration (p = 0.11). The NTG infusion consistently decreased pressure determinants of myocardial oxygen demand without increasing heart rate. NTG also decreased a calculated coronary collateral resistance index in 13 patients. Responsiveness to NTG did not appear to depend on the presence or absence of collateral vessels detected by angiography or on any other angiographic variable assessed. Measurement of coronary collateral function during coronary angioplasty is a new technique with the potential to assess the ability of interventions to prevent transient myocardial ischemia and improve myocardial perfusion during acute coronary occlusion in humans.

Nitrate delivery systems in perspective. A decade of progress

In recent years the use of nitroglycerin and long-acting nitrate compounds in clinical practice has been increasing. Only 10 to 15 years ago these drugs, at least in oral formulation, were felt to have no clinical utility because of concern that potent hepatic enzyme activity would degrade sufficient amounts of the nitrate compounds from reaching the systemic circulation. However, it is now recognized that oral nitrate administration when given in sufficient amounts achieves therapeutic plasma concentrations and desired clinical effects. Nitrates are routinely used for the treatment of stable and unstable angina and also play a role in therapy for complications of myocardial infarction. Nitrates are very effective agents for preload reduction in vasodilator therapy of congestive heart failure. A wide variety of nitrate delivery systems, including the standard oral and sublingual formulations, and as well as the new transdermal nitroglycerin discs and buccal nitroglycerin, are now available. Sublingual nitroglycerin, isosorbide dinitrate, and buccal nitroglycerin are used for acute treatment of attacks of ischemic chest pain. For ambulatory patients, long-acting therapy can be administered by oral, topical ointment, transdermal disc, and buccal nitroglycerin formulations. Each compound has a slightly different onset and duration of action, which is in part dose-dependent. The relative merits and problems with each of the formulations are reviewed. Intravenous nitroglycerin is now commercially available and plays an increasing role in the intensive care units. It is an ideal drug for acute chest pain syndromes, including acute myocardial infarction. Specialized tubing does not need to be employed. The wide variety of nitrate delivery systems available to physicians makes use of this tried and true therapy practical and easy to carry out for clinicians.

Radionuclide assessment of cardiac function. Pre-operative evaluation of patients with abdominal aortic occlusive disease undergoing aortobifemoral bypass grafting

Pre-operative radionuclide angiography, a non-invasive technique for evaluating ventricular function, was performed on 34 consecutive patients undergoing aortobifemoral bypass grafting for abdominal aortic occlusive disease, to determine whether pre-existing coronary artery disease causes significant modification of cardiac function. Patients were divided into two groups according to medical history. Group I had 23 patients with no symptoms of coronary artery disease and Group II had 11 patients, six with previous myocardial infarction and five with angina pectoris. There was a significant difference in left ventricular ejection fraction and in cardiac output between these two groups. A flow-directed pulmonary artery catheter was inserted in eight patients in Group II who had an ejection fraction less than 50% and a nitroglycerin infusion was used in six cases to maintain pulmonary capillary wedge pressure below 20 mmHg. In the other patients, only central venous pressure was monitored. All patients had uneventful operative courses. It is concluded that left ventricular function is significantly altered in patients with symptoms of both abdominal aortic occlusive disease and coronary artery disease. By contrast, cardiac function is normal in patients free from symptoms of coronary artery disease, and central venous pressure monitoring seems sufficient in the management of these patients during aortobifemoral bypass grafting.

Rational medical therapy for stable angina pectoris

Important advances in understanding of the pathophysiology and medical treatment of angina pectoris have taken place in the past few years. Angina may occur from increased oxygen demands that cannot be met by a diseased coronary circulation and/or primary decrease in oxygen supply to the heart. Three major categories of pharmacologic agents are used in treating angina. Nitrates remain the first-line approach; they are inexpensive and available in many delivery forms. Beta blockers are also effective in the treatment of angina pectoris, and despite their side effects, are particularly useful in effort angina. The newest agents, the calcium channel blockers, are efficacious in all types of anginal syndromes. Each group of drugs acts differently on the various pathophysiologic mechanisms that contribute to the production of angina. This commentary critically reviews the major groups of anti-anginal drugs and places them in a clinical perspective. Guidelines for choosing an appropriate agent for the treatment of angina are proposed. Special situations, such as angina and hypertension, congestive heart failure, or post-myocardial infarction angina, are discussed with respect to selection of anti-anginal therapy. The proper utilization of nitrates, calcium channel blockers, and beta blockers, alone or in combination, provides a bright future for patients with ischemic heart disease.

Comparison of the antianginal effectiveness of nifedipine, verapamil, and isosorbide dinitrate in patients receiving propranolol: a double-blind study

Ten men with stable angina not fully relieved by optimal doses of propranolol were given on each of four mornings a single dose of 10 mg nifedipine, 120 mg verapamil, isosorbide dinitrate (5 to 30 mg, previously titrated to lower systolic blood pressure by 15 to 20 mm Hg), or placebo, in double-blind fashion. Bicycle exercise to angina was performed hourly for 8 hr thereafter. All three vasodilators increased exercise time by at least 50% by the first hour (p less than .001), with a gradually diminishing effect persisting for 6 to 8 hr (p less than .01). Although for the group there were no differences in magnitude and duration of effect among the three drugs, in five of the individual patients there were important differences in response favoring one or another vasodilator. We conclude that nifedipine, verapamil, and isosorbide dinitrate are equally effective and reasonably long-acting antianginal supplements to propranolol, although some patients may benefit more from one than another of the three.

Vasodilator therapy in chronic congestive heart failure

Vasodilator agents are relatively new additions to the armamentarium for the management of patients with congestive heart failure. Myocardial failure, irrespective of the aetiology, tends to create a vicious cycle characterised by reduced cardiac output and elevated systemic vascular resistance, which further decrease cardiac output by increasing left ventricular ejection impedance. The rationale for the use of vasodilators is to interrupt the vicious cycle by decreasing the left ventricular ejection impedance by peripheral vasodilatation. Although most vasodilator agents produce qualitatively similar haemodynamic responses, quantitatively their haemodynamic effects differ considerably. Knowledge of the haemodynamic effects of the various vasodilators helps in the selection of a particular drug for the management of such patients. This article reviews the mechanisms of action, haemodynamic effects, pharmacokinetics, clinical usage and adverse effects of non-parenteral vasodilator agents currently available for the management of patients with chronic heart failure.

Regional coronary venous flow responses to transient coronary artery occlusion in human beings

Coronary hemodynamic responses to transient coronary artery occlusion in 21 patients were investigated by using regional coronary venous thermodilution to measure regional coronary venous flows. Transient coronary artery occlusion was produced by coronary artery spasm (13 patients) or balloon inflation during coronary angioplasty (8 patients). The left anterior descending coronary artery was transiently occluded in 12 patients, the right coronary artery in 8 patients and the left circumflex artery in 1 patient. During transient coronary occlusion, regional venous flow decreased in 20 of the 21 patients (79 +/- 31 to 53 +/- 29 ml/min, mean +/- standard deviation [SD]; probability [p] less than 0.05) corresponding to the left ventricular region perfused by the occluded artery. Regional coronary resistance increased in all 21 of these regions (1.42 +/- 0.75 to 2.26 +/- 1.45 mm Hg/ml per min, p less than 0.05). Simultaneously measured blood flow and resistance in the left ventricular region supplied by the nonoccluded arteries did not change significantly (62 +/- 27 to 64 +/- 29 ml/min and 1.85 +/- 0.93 to 1.81 +/- 0.98 mm Hg/ml per min, respectively). Coronary hemodynamic changes were similar during transient coronary occlusion, whether produced by coronary spasm or by balloon inflation. However, the presence of angina, reversible electrocardiographic abnormalities and an increase of the left ventricular filling pressure were more common during coronary spasm (p less than 0.05 for all). Regional coronary hemodynamic changes during transient occlusion of the anterior descending, circumflex or right coronary artery were similar. These data show that coronary occlusion decreases regional left ventricular flow in the region perfused by the affected artery. The method of coronary occlusion or the coronary artery affected during occlusion did not seem to elicit different responses.

Cutaneous administration of nitroglycerin: a review

Chronic administration of nitroglycerin may have important therapeutic effects in patients with angina, acute myocardial infarction, congestive heart failure and peripheral vascular disease. Because of unpredictable oral absorption and short duration of action, topical preparations provide an alternative mode of administration. New controlled release transdermal preparations appear to produce constant plasma nitroglycerin concentrations of 0.2-0.3 ng/ml that persist for up to 24 hours. Additional clinical trials of the therapeutic response to this drug form are necessary, particularly in regard to the relative hemodynamic efficacy and side-effect profile of sustained vs. fluctuating plasma nitroglycerin concentrations.

The additive antianginal action of oral isosorbide dinitrate in patients receiving propranolol. Magnitude and duration of effect

Ten men with stable angina not completely relieved by full doses of propranolol (mean, 218 mg daily) were given double-blind, on alternate mornings, a placebo or an oral dose (5 to 30 mg) of isosorbide dinitrate (ISDN) previously titrated to lower sitting systolic blood pressure by 20 mm Hg. Patients had been trained in a protocol which precipitated angina after three to six minutes of bicycle exercise. On test days, with propranolol continued, bicycle exercise was performed until the appearance of angina before ISDN or placebo administration, and hourly thereafter for eight hours. Mean exercise duration was greater one hour after ISDN than after placebo by 182 sec (423 +/- 39 vs 241 +/- 13, p less than 0.001), and a difference of 63 sec was still present at six hours (p less than 0.002). At one hour, ISDN lowered resting systolic blood pressure by 26 mm Hg (from 114 +/- 5 mm Hg to 88 +/- 4 mm Hg; p less than .001) without appreciably changing heart rate. We conclude that ISDN is a very effective and reasonably long-acting antianginal supplement to propranolol.

Effects of nitroglycerin on isometric exercise

Eight patients with ischemic heart disease performed isometric handgrip of five minutes' duration at 30% of their maximum voluntary contraction, before and after administration of 0.4 mg sublingual nitroglycerin (NTG). Although isometric exercise resulted in similar rise of left ventricular systolic pressure (LVSP) before and after NTG, the level of LVSP during the post NTG effort was lower. Heart rate, cardiac index, stroke index, left ventricular stroke work index, and systemic resistance were not different during the pre- and post NTG exercise. Left ventricular end-diastolic pressure rose to a significantly lower level (18.3 +/- 14.4 mm Hg) during the post NTG handgrip than during the pre NTG effort (31.4 +/- 17.6 mm Hg, P less than 0.005). It is concluded that NTG reduces preload and afterload both at rest and during isometric exercise and improves left ventricular performance during isometric exercise.

Regional coronary blood flow during relief of pacing-induced angina by nitroglycerin. Implications for mechanism of action

The mechanism for the therapeutic effect of nitroglycerin in stress-induced angina remains controversial; it has been attributed to both increased blood supply to the ischemic myocardium and decreased myocardial oxygen demand. To investigate the contribution of each of these mechanisms, systemic pressures and great cardiac vein flow were measured in 14 patients with single-vessel disease involving the left anterior descending (LAD) coronary artery during the development of pacing-induced angina and after the administration of nitroglycerin while continuing pacing at the angina-provoking rate. Great cardiac vein flow, measured by thermodilution, represents the venous efflux from the LAD territory and therefore provided an index of flow to the poststenotic myocardium. In 11 patients, nitroglycerin was administered systemically (400 to 800 micrograms sublingually or 200 micrograms intravenously); angina was relieved in 10, concomitant with a decrease in both great cardiac vein flow (from 123 +/- 29 to 98 +/- 29 ml/min, p less than 0.001) and mean aortic pressure (from 118 +/- 22 to 104 +/- 22 mm Hg, p less than 0.001). In contrast, when 75 micrograms of nitroglycerin was administered directly into the left main coronary artery of 7 patients, it produced a small increase in great cardiac vein flow (from 108 +/- 32 to 125 +/- 31 ml/min, p = 0.059), no change in aortic pressure, and no relief of angina. This study suggests that nitroglycerin's major beneficial action in pacing-induced angina is unrelated to direct effects on the coronary circulation and is likely related to its cardiac unloading effect.

Pharmacologic effects of a nitrate coronary vasodilator on cardiac perfusion and function, measured semiquantitatively

Peritrate (pentaerythritol tetranitrate), a nitrate coronary vasodilator, was capable of significantly increasing perfusion and function in ischemic heart muscle. The A2 image-processing computer with software developed by Burow was used to evaluate regional perfusion and segmental wall motion in six patients with ischemic areas in the myocardium. These image-processing techniques were satisfactory for evaluation of ischemic heart muscle.

The use of intravenous nitroglycerin in cardiovascular disease

The development of an intravenous form of nitroglycerin has further enhanced the role of nitrates in the therapy of cardiovascular disorders. This new preparation permits prompt initiation of therapy and rapid attainment of high systemic levels; because of its short half-life, rapid dose titration is both feasible and safe. The antianginal effects of intravenous nitroglycerin are useful in the treatment of coronary vasospasm and unstable angina pectoris. Its hemodynamic effects are of benefit in the therapy of congestive heart failure and in the control of peri-operative hypertension. Recent data suggest that, with appropriate monitoring, intravenous nitroglycerin can be safely administered to patients with evolving myocardial infarction to reduce the extent of myocardial damage.

Effect of coronary vasodilating drug on myocardial work

The purpose of this paper is to show, by noninvasive measurements, previously undocumented effects on cardiac work of the nitrate coronary vasodilator Pentaerythritol Tetranitrate (Peritrate). The chew-and-swallow 40-mg tablets of this drug were given to 10 patients of type II AHA classification. The Diastolic Time Tension Index/Systolic Time Tension Index Ratio increased significantly from 1.15 (+/- 0.11 SEM) to 1.46 (+/- 0.13), p less than 0.05. The Double Product decreased significantly from 9813 (+/- 606) to 8336 (+/- 497), p less than 0.01. The Triple Product also decreased significantly from 3223 (+/- 235) to 2425 (+/- 206), p less than 0.01. The percent diastole of the R-R interval increased significantly from 65% (+/- 2.44) to 70% (+/- 1.73) p less than 0.05, while no significant change in heart rate occurred (63.2 bts/min to 62.4 bts/min). Correspondingly, there was a decrease of systolic time interval, from 0.33 second (+/- 0.2) to 0.29 second (+/- .01) p less than 0.01. A significant decrease in blood pressure was also noted. Systolic BP dropped from 155 (+/- 8.0) to 134 (+/- 7.2), p less than 0.01. Diastolic BP dropped from 89.2 (+/- 2.8) to 79.2 (+/- 2.2), p less than 0.01. This study shows that Peritrate produced significantly favorable changes in all the cited indicators of cardiac work.

Glyceryl trinitrate (nitroglycerin) ointment and isosorbide dinitrate: a review of their pharmacological properties and therapeutic use

Sublingual glyceryl trinitrate (nitroglycerin) is the most widely used drug in the treatment of angina pectoris, but its use is limited due to its short acting effect. Recent investigations have shown that some longer acting nitrates administered orally or topically have a long acting antianginal effect. The mechanism of the antianginal effect of nitrates is multifactorial. Nitrates increase oxygen supply to the myocardium by causing redistribution of coronary blood flow. In addition, nitrates decrease myocardial oxygen demand by reducing left ventricular volume, intramyocardial tension, and left ventricular afterload. The use of nitrates for the treatment of congestive heart failure has also been established in recent years. Nitrates have a predominant venodilatory effect resulting in peripheral blood pooling and decreased venous return to the heart, thereby decreasing left ventricular filling pressure. The effect of nitrates on the arteriolar circulation is small, and there is usually little or no change in cardiac output. Some reduction in systemic blood pressure can be seen, while there is usually no change in heart rate. In a small number of patients with myocardial infarction complicated by congestive heart failure, the use of long acting nitrates has resulted in haemodynamic and symptomatic improvement. Nitrates has also bee shown to improve variant angina. Nitrates are usually well tolerated in most patients. However, some troublesome side effects can occur, including headache, postural hypotension, and methaemoglobinaemia.

[Prevention of per-operative myocardial ischemia with continuous nitroglycerin infusion]

The aim of this work is to assess the possible beneficial effects of intra and post operative nitroglycerin infusion in patients with disabling angina pectoris (Class III of the New-York Heart Association). We thus compared the occurrence of myocardial ischemia detected by means of continuous electrocardiographic recording of lead V5 in 31 patients which were divided in two groups. The control group (I) included 16 patients, group II included 15 patients undergoing similar surgical procedures, given a permanent nitroglycerin infusion. Mean dose of nitroglycerin was 0,91 +/- 0,18 micrograms . kg-1 . min-1. An ischemic type S T segment depression occurred in 15 out 16 patients in group I and in only 3 out of 15 patients in group II (p less than 0,001). No S T segment depression occurred following a decrease of more than 25 p. 100 in systolic blood pressure in 8 patients of group II at the time of induction. These hypotensive episodes were easily corrected by decrease of the nitroglycerin infusion rate associated with a rapid blood volume expansion. The very high incidence of intra operative myocardial ischemia in control group demonstrates the severity of the coronary disease in the observed patients. The significantly lower frequency of ischemic S T segment depression observed in the patients given nitroglycerin infusion suggests that this drug is highly effective in preventive myocardial ischemia in patients with severe coronary artery disease. The administration of nitroglycerin in our patients had been easy to control, blood pressure reaching normal value within a few minutes after decrease of the rate of drug infusion when needed.

Effect of nitroglycerin on ST potentials in the post-acute phase of myocardial infarction

Thoracic electromaps were recorded before and after sublingual nitroglycerin (NG) in 26 subjects 15 and 30 days after acute myocardial infarction (MI), in order to evaluate the effect of the drug on injury potentials. Ten patients with documented left ventricular aneurysm were also studied 5 to 46 months after acute MI. Fifteen min after NG there was a significant decrease, compared with basal values, of ST segment elevations, blood pressure and rate-pressure product on both the 15th and 30th days. The degree of ST potentials reduction was not strictly related to the decrease of myocardial oxygen consumption, as indicated by the rate-pressure product. The response to NG on the 15th day did not predict accurately the evolution of injury potentials. In fact there was no significant correlation between percentages reduction of ST after NG on the 15th day and amplitudes of ST segment elevations present on the 30th day. In the patients with ventricular aneurysm, ST potential decrease and hemodynamic changes after NG were similar to those observed in the other groups studied. Our data suggest that it is not possible to differentiate between ST segment elevations associated with a dyssynergic area and those merely due to ischemic injury on the basis of NG sensitivity, and that ST segment elevations in the acute and subacute phase and long after MI have, at least in part, a similar electrophysiological significance.

Magnitude of dilatation of large and small coronary arteries of nitroglycerin

Vasodilatory responses of segments of large epicardial left coronary artery (CA), small intramyocardial CAs (0.3-1.0 mm), coronary stenoses and CAs filled by collaterals were determined in 34 patients. Measurements were made before and after nitroglycerin (0.4 mg, sublingual) by means of quantitative magnification coronary angiography using photospot film and a calibrated 6-power viewing device. The left main CA, proximal, middle and distal anterior descending and circumflex segments, and small CAs showed dilatation that varied in magnitude. When magnitude of dilatation was compared with control diameter of the vessel and its location, control diameter proved to be the significant independent variable. CAs with the smallest control diameter showed the greatest magnitude of vasodilatation. CA branches filled by collaterals had vasodilatation similar in magnitude to that of CAs of comparable control diameter. Although coronary stenoses dilated, the magnitude of dilatation was less than that observed in nonstenosed arterial segments of similar control diameter. When areas of stenosis were excluded, however, results were similar regardless of whether the patient had CA disease. These data indicate that a principal determinant of the CA vasodilatory response to nitroglycerin is the size of the artery before nitroglycerin.