Radionuclide assessment of nitroglycerin influence on abnormal left ventricular segmental contraction in patients with coronary heart disease

Efficacy of different forms of nitrates in angina pectoris

Nitroglycerin has maintained its position in the treatment of angina pectoris for more than a century. Efficacy of oral nitrates has been established and compares well with that of other anti-anginal drugs. New delivery systems are being developed for sustained systemic nitrate action. Beneficial action of nitrates in congestive heart failure and their crucial role in unstable angina and acute myocardial infarction has further widened their therapeutic use. A plausible hypothesis of the mechanism of nitrate-induced vasodilation has been presented, involving production of nitrosothiols and activation of guanylate cyclase in the vascular smooth muscle. Recent developments suggest that the rate degradation of nitrates and formation of nitrosothiols in the vascular smooth muscle are linked, offering an explanation to the relatively rapidly developing, but partial vascular tolerance during high-dose nitrate therapy.

Dobutamine-induced ST-segment elevation in patients with healed myocardial infarction. A marker of myocardial viability

The purpose of this study was to determine the significance of transient ST-segment elevation during dobutamine infusions in patients with healed Q wave myocardial infarction. Twenty-seven patients with previous Q wave myocardial infarction were studied prospectively with dobutamine-thallium-201 single-photon emission computed tomography. The presence of ST-segment elevation in leads with Q waves was related to thallium reversibility at 4-hour redistribution imaging or after reinjection, to residual flow, as well as to wall motion abnormalities in the infarcted zone. ST-segment elevation in infarct-related leads was observed in 15 patients; 11 (73%) showed viability by thallium-201 in the infarcted zone. In patients without ST-segment elevation, viability was shown less frequently (33%, P < .05). Hypokinesis in infarcted segments was present in 60% of patients with ST-segment elevation and in 25% of patients without ST-segment elevation (.05 < P < .1). Finally, infarct-related artery was patent and/or collaterals were present in 10 patients with ST-segment elevation (67%) and in 4 patients without (33%, .05 < P < .1). In conclusion, ST-segment elevation during dobutamine infusion is a marker of residual viability in infarcted segments.

Detection of viable tissue in healed infarcted myocardium by dipyridamole thallium-201 reinjection and regional wall motion studies

Reinjection imaging with thallium-201 (Tl-201) may provide a convenient method of assessing myocardial viability. Twenty patients with a previous Q-wave healed myocardial infarction were examined to evaluate the detection of viable tissue in infarcted segments. All patients underwent to evaluate the detection of viable tissue in infarcted segments. All patients underwent dipyridamole Tl-201 tomographic imaging with reinjection of 1 mCi of Tl-201 after redistribution. Radionuclide ventriculography was performed before and after administration of 5 mg of dinitrate isosorbide sublingually for regional wall motion analysis. Patients presented with 38 fixed defects, 12 of which demonstrated improved Tl-201 uptake on reinjection; 10 of 12 reinjection-reversible segments were hypokinetic or normal after administration of nitrates, whereas 22 of 26 nonreversible segments remained akinetic or dyskinetic (p < 0.001). Of 20 patients, 9 had reinjection-reversible segments; coronary angiography revealed a patent infarct-related artery or collaterals, or both, in 7 of these patients. The infarct-related artery was patent or collaterals were present, or both, in 4 of 11 patients who did not improve with reinjection. It is concluded that reinjection of Tl-201 during dipyridamole Tl-201 scintigraphy may frequently detect viable tissue in infarcted segments in patients with a Q-wave infarction. Segments with reinjection reversibility usually do not remain dyskinetic or akinetic after administration of nitrates and have some residual flow on coronary angiography.

A study of ventricular contraction sequence in complete right bundle branch block by phase analysis

Twenty-four patients with complete right bundle branch block (CRBBB) combined with and without left axis deviation (LAD) on ECG, were compared with 17 normal subjects to evaluate the right ventricular contraction sequence and pattern in detail. Blood pool scintigrams were obtained in the left anterior oblique projection, and these images were analyzed by first component Fourier harmonics. In the normal subjects, the phase value distribution representing the pattern of ventricular contraction was almost homogeneous in both the right and left ventricles (RV & LV). In the CRBBB patients without LAD, the phase images showed apparent phase delay in the right ventricle. In the CRBBB patients with LAD, the phase images showed many different contraction patterns varying from normal to RV phase delay, owing to the effects of the hemi-block. Quantitative analysis of the absolute values, showed that the mean (RV-LV) value was 6.6 +/- 8.4 msec in the normal subjects. In the CRBBB patients without LAD, the duration of the QRS complex correlated with the mean (RV-LV) value, whereas no difference was observed between the duration of the QRS complex and the standard deviation of the right ventricle. Using phase analysis the degree of the RBBB can be determined from the phase images, and can be quantitatively analyzed as in electrical studies.

Role of radionuclide ventriculography in evaluating cardiac function

The role of nuclear cardiology techniques for evaluating cardiac function has become increasingly important among other diagnostic techniques. The current status of radionuclide imaging of left and right ventricular function allows accurate diagnosis of cardiac patients with both coronary and noncoronary disease. The combination of gated first-pass and equilibrium radionuclide ventriculography makes it possible to assess more completely cardiac function than by either technique alone. Of particular interest to most imaging physicians is the current position of exercise ventriculography in the diagnostic setting, especially since this test has undergone new scrutiny in its application to broader patient segments. This technique and issues related to its place in the diagnostic environment are discussed in this review article, with emphasis on relevance to the clinical laboratory.

Nitrates: why and how should they be used today? Current status of the clinical usefulness of nitroglycerin, isosorbide dinitrate and isosorbide-5-mononitrate

Nitrates are highly effective both in terminating acute attacks of angina pectoris and in the prophylaxis of symptomatic and asymptomatic myocardial ischemia. Preload reduction by venodilatation is the prevailing mechanism of nitrates in patients with chronic stable angina and is the unique feature distinguishing them from beta and calcium-channel blockers. Nitrates dilate coronary arteries not only in pre- and poststenotic vessels, but also in eccentric lesions. In patients with endothelial dysfunction, nitrates seem to be the physiological substitute for endothelium-derived relaxing factor. During the past decade, however, there has been substantial evidence of a clinically relevant loss of the anti-ischemic effects ("nitrate tolerance"). Many studies with oral dosing of isosorbide dinitrate or isosorbide-5-mononitrate at least three times daily have proven nitrate tolerance in patients with coronary artery disease and/or congestive heart failure. Complete loss of anti-ischemic effects after repetitive, continuous patch attachments has also been found. As we first showed in 1983, intermittent therapy with once-daily ingestion of high-dose sustained-release isosorbide dinitrate was successful in preventing the development of tolerance. Similarly, tolerance to isosorbide-5-mononitrate also does not develop when it is ingested once daily. It is now generally accepted that a daily low-nitrate interval is required to prevent tolerance development. Although the minimal patch-free interval required to prevent tolerance needs further investigation, a 12-h patch-free interval should prevent tolerance in most patients. The prolonged duration of action of once-daily high-dosage administration of sustained-release formulations, the improved patient compliance with a single daily administration, and the increased likelihood of maximal anti-ischemic effects are important reasons for recommending high single daily doses of isosorbide dinitrate or isosorbide-5-mononitrate.

Nuclear magnetic resonance and radionuclide angiographic assessment of acute myocardial infarction in a randomized trial of intravenous streptokinase

Sixty-six patients presenting with their first evolving transmural acute myocardial infarction (AMI) were randomized to receive either streptokinase (n = 41) or placebo therapies (n = 25) within 6 hours of the onset of chest pain. These patients then underwent supine rest, exercise and after-nitroglycerin radionuclide angiography 3 weeks after AMI. Nuclear magnetic resonance (NMR) imaging was performed at 3 weeks as a more direct estimate of AMI size. Although peak creatine kinase values were comparably elevated between groups (2,367 +/- 1,486 IU/liter for streptokinase vs 2,637 +/- 1,305 IU/liter for placebo), there was a significant reduction in NMR-measured AMI size in the streptokinase group (3 +/- 2% of left ventricular volume vs 10 +/- 4% in the placebo group, p less than 0.05). This occurred despite comparable resting (54 +/- 11 vs 47 +/- 10% and exercise (53 +/- 12 vs 49 +/- 11%) global ejection fractions. However, following nitroglycerin, there was an improvement in global ejection fraction in the streptokinase-treated group that was not observed with placebo (61 +/- 13 vs 48 +/- 10%, p less than 0.05). A similar pattern was also observed with regional functional analysis. Thus, streptokinase therapy leads to a significant reduction in NMR-measured AMI size and to a greater degree of reversible left ventricular dysfunction.

Acute effects of sublingual isosorbide dinitrate on global and regional left ventricular diastolic filling in normal persons

To study the acute effects of isosorbide dinitrate (ISDN) on global and regional left ventricular (LV) diastolic filling, gated radionuclide ventriculographic studies were conducted in 21 normal persons before and after sublingual administration of ISDN. ISDN treatment caused significant increases in ejection fraction and peak LV ejection rate and it caused a delay in occurrence of peak LV filling, without statistically significant changes in peak LV filling rate globally and regionally. The ratios of peak LV filling rate to peak LV ejection rate decreased significantly both globally and regionally. These alterations induced by ISDN could be interpreted as indicating a failure of improvement of the early diastolic filling despite increased systolic function and heart rate in the global left ventricle and in regions of the left ventricle. Furthermore, ISDN caused early diastolic asynchronous filling. There was a negative correlation between this early diastolic asynchronous filling and the ratio of global peak LV filling to global peak LV ejection rate (r = -0.66, p less than 0.001), indicating that administration of ISDN to normal persons may produce early diastolic asynchronous filling associated with failure of improvement of diastolic filling despite increased systolic function and heart rate.

Newer technologies for study of the action of nitrates in coronary circulation and myocardial function

Minimally invasive evaluation of the behavior of the right and the left ventricle can be obtained in a dynamic way by using technetium-99 (99Tc) scintographic ventriculography. The "first pass" technique is particularly appropriate to the investigation of short-acting agents, such as nitroglycerin and other nitrates, but information on a 1-minute to 2-minutes steady state response can be obtained by using the "gated blood pool" method. Studies in patients with and without coronary heart disease have identified apparent improvement in regional and global left ventricular ejection fractions associated with afterload reduction caused by such interventions. However, part of the normalization of regions of previously abnormal myocardial contraction may be due to more uniform transmural distribution of coronary blood flow. Such techniques, including nitrate administration, have been used to define regional ischemia suitable for revascularization procedures. Sequential thallium studies also suggest that nitroglycerin reduces or prevents stress induced ischemia, although the mechanism (afterload versus coronary vasodilation) has not been completely elucidated. In the future subtraction angiographic techniques may lead to a more accurate estimate of regional distribution of blood flow and its pharmacologic manipulation. Digital techniques will also facilitate accurate measurement of coronary vascular narrowing in a manner that will serve to elucidate the direct actions of nitrates and similar substances on the coronary circulation.

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.

Exercise radionuclide ventriculography in evaluating successful transluminal coronary angioplasty

To evaluate the ability of transluminal coronary angioplasty (TCA) to relieve myocardial ischemia, 44 patients with single vessel disease underwent exercise gated radionuclide ventriculography (GRNV) before and 2.8 +/- 1.3 days following angiographically successful TCA. Pre-TCA GRNV was abnormal in 11 of 14 patients with right coronary artery (RCA) stenosis and 24 of 30 with left anterior descending (LAD) stenosis. Following TCA there was an increase in exercise duration from 500 +/- 288 sec to 625 +/- 273 sec (P less than 0.001), and in maximum double product from (209 +/- 69) x 10(2) to (263 +/- 70) x 10(2) (P less than 0.001). The number of patients with stress-induced ST-T abnormalities decreased from 13 to 4 (P less than 0.05), and the number with chest pain during exercise decreased from 18 to one (P less than 0.001). Whereas resting ejection fraction was unchanged (0.58 +/- 0.10 vs 0.59 +/- 0.11) following TCA, the ejection fraction at peak exercise increased from 0.61 +/- 0.13 to 0.66 +/- 0.12 (P less than 0.001). Of 24 patients with resting abnormalities, regional wall motion improved in 13. In 22 of 31 patients with stress-induced asynergy, the wall motion response to exercise improved (P less than 0.001). Of 19 patients restudied angiographically and with exercise GRNV at 6-12 months, restenosis of greater than or equal to 50% had occurred in six, four of whom had abnormal studies. In six of whom the degree of stenosis of the dilated artery had remained less than or equal to 20% the exercise GRNV study remained normal. It is concluded that GRNV is helpful in documenting the improvement in resting left ventricular function and functional reserve in patients with angiographically successful TCA. In the limited number of patients with late follow-up studies, data suggest that GRNV may be a valuable test to detect restenosis.

An accurate means of detecting and characterizing abnormal patterns of ventricular activation by phase image analysis

The ability of scintigraphic phase image analysis to characterize patterns of abnormal ventricular activation was investigated. The pattern of phase distribution and sequential phase changes over both right and left ventricular regions of interest were evaluated in 16 patients with normal electrical activation and wall motion and compared with those in 8 patients with an artificial pacemaker and 4 patients with sinus rhythm with the Wolff-Parkinson-White syndrome and delta waves. Normally, the site of earliest phase angle was seen at the base of the interventricular septum, with sequential change affecting the body of the septum and the cardiac apex and then spreading laterally to involve the body of both ventricles. The site of earliest phase angle was located at the apex of the right ventricle in seven patients with a right ventricular endocardial pacemaker and on the lateral left ventricular wall in one patient with a left ventricular epicardial pacemaker. In each case the site corresponded exactly to the position of the pacing electrode as seen on posteroanterior and left lateral chest X-ray films, and sequential phase changes spread from the initial focus to affect both ventricles. In each of the patients with the Wolff-Parkinson-White syndrome, the site of earliest ventricular phase angle was located, and it corresponded exactly to the site of the bypass tract as determined by endocardial mapping. In this way, four bypass pathways, two posterior left paraseptal, one left lateral and one right lateral, were correctly localized scintigraphically. On the basis of the sequence of mechanical contraction, phase image analysis provides an accurate noninvasive method of detecting abnormal foci of ventricular activation.

Phase image characterization of ventricular contraction in left and right bundle branch block

The phase image is a computer-derived functional image, based on the analysis of the time versus radioactivity curve in each pixel location of the multiple gated blood pool scintigram. Within the ventricular regions of interest, the phase angle is roughly equivalent to the time of onset of counts reduction or to the time of onset of ventricular contraction and is expressed in degrees from 0 to 360 degrees. A gray scale-coded image of such a regional phase angle, the phase image, can be looked on as a map of sequential contraction. This method was applied in 33 patients without severe contraction abnormality including 16 patients with normal conduction, 9 with right bundle branch block and 8 with left bundle branch block. In patients with normal conduction the pattern of phase angle distribution, representing the pattern of ventricular contraction, was homogeneous and symmetric in both the left and right ventricles. Analysis in this normal group indicated a slight but significant difference between the mean (+/- standard deviation) phase angle of the left ventricle (8.5 +/- 11.8 degrees) and that of the right ventricle (13.6 +/0 12.9 degrees, p = 0.01). There was a slight, but nonsignificant difference between mean intrapatient left and right ventricular phase angle onset (1.9 +/- 6.5 degrees). The mean phase angle of the right ventricle in patients with right bundle branch block (27.6 +/- 14.2 degrees) and of the left ventricle in those with left bundle branch block (21.9 +/- 14.0 degrees) was delayed compared with that in patients with normal conduction (p less than 0.05 for both). The mean intrapatient difference between left and right ventricular mean phase angles in patients with normal conduction (-5.2 +/- 6.8 degrees) was significantly different from that in patients with right (-21.8 +/- 10.3 degrees, p less than 0.001) or left (21.8 +/- 6.8 degrees, p less than 0.001) bundle branch block. The mean intrapatient difference between onset of left and right ventricular phase angles was also significantly different from normal in patients with right (-10.6 +/- 7.5 degrees, p less than 0.005) or left (18.7 +/- 8.3 degrees, p = 0.01) bundle branch block. Although phase imaging is not without artifactual error, this study demonstrates that the phase image can characterize familiar conduction abnormalities. It presents the potential for application as a general noninvasive tool in the investigation of the timing and sequence of ventricular contraction in patients with normal or abnormal ventricular activation.

Factors that affect the reproducibility of measurements of left ventricular function from first-pass radionuclide ventriculograms

To examine which factors affect the reproducibility of ejection fraction (EF), pulmonary transit time (PTT) and segmental wall motion assessed from first-pass radionuclide angiograms (FPRA), 32 patients who had FPRA were randomized for site of injection of isotope (right or left arm) and projection (right or left anterior oblique [RAO or LAO]). The quality of injected bolus was measured from the full width at half maximum (FWHM) of the bolus time-activity curve in the superior vena cava. All patients had two sequential studies on each of two consecutive days, and each study was analyzed independently by two observers. For EF, inter- and intraobserver correlations ranged from 0.94-0.98. EF was higher in the RAO than the LAO projection (mean 47.4% vs 40.3%, p less than 0.001), but neither injection site nor bolus FWHM affected the results. For PTT, interobserver correlations ranged from 0.75-0.93 and intraobserver correlations from 0.61-0.85. Variability in PTT was large, and inter- and intraobserver variabilities were directly related to bolus FWHM (mean 0.60 +/- 0.21 second for interobserver differences in PTT of less than 2.0 seconds, mean 1.55 +/- 0.86 seconds for interobserver differences in PTT of greater than 2 seconds [p less than 0.005]). Differences in FWHM between sequential studies were 0.28 +/- 0.29 second when intraobserver differences in PTT were less than 2 seconds and 1.04 +/- 0.67 seconds when differences in PTT were greater than 2.0 seconds (p less than 0.005). Variations in PTT were not related to differences in projection or injection site. Wall motion was highly reproducible for both projections. In the RAO projection, one of 116 anterior segments (0.9%), one of 116 apical segments (0.9%), and four of 116 inferior segments (3%) were judged normal from one observer's images and abnormal from another. In the LAO view, discrepancies occurred in one of 126 septal segments (0.8%), two of 126 apical segments (1.6%) and four of 126 posterolateral segments (3%). This study shows that EF and wall motion are highly reproducible in any projection, but the choice of projection significantly affects the values for EF from FPRA. PTT measurements are less reliable, highly bolus dependent, and their use in clinical practice depends on quality control of the bolus of injected radionuclide.

Vasodilator therapy in refractory congestive heart failure: a comparative analysis of hemodynamic and noninvasive studies

The response to vasodilator therapy was assessed in 12 patients with chronic severe congestive heart failure refractory to conventional treatment. Cardiac output and intraarterial and pulmonary capillary wedge pressures were recorded continuously to assess the hemodynamic response to the vasodilators used. Control and post-treatment M mode echocardiograms and radionuclide angiograms were obtained to assess the change in left ventricular size and ejection fraction concurrent with the hemodynamic improvement. Despite a 33 percent decrease in pulmonary capillary wedge pressure (p less than 0.001) and a 35 percent increase in cardiac index (p less than 0.001), no significant change occurred in left ventricular end-diastolic or end-systolic chamber size on echocardiography or in ejection fraction measured with radionuclide angiography. In this study M mode echocardiography and radionuclide angiography were of no value in monitoring the actual hemodynamic response to vasodilator therapy in this group of patients with a left ventricular ejection fraction of less than 30 percent.

Natural history of contractile abnormalities after acute myocardial infarction in man: severity and response to nitroglycerin as a function of time

The natural history of contraction abnormalities and their response after acute myocardial infarction in man were studied using radionuclide angiography. Sixteen patients were studied before and after sublingual nitroglycerin within 24 hours, 5-7 days and 4-6 weeks after the onset of chest pain. Within 24 hours, central chord shortening in the zone of infarction was reduced to 13.1 +/- 9.8%, but improved 27.2 +/- 18.4% (p less than 0.001) after nitroglycerin. After 5-7 days, central chord shortening improved similarly, but less markedly, from 12.9 +/- 9.2% to 24.4 +/- 13.2% (p less than 0.001). After nitroglycerin 4--6 weeks after the acute myocardial infarction, the central chord showed no response to nitroglycerin; it was 13.9 +/- 10.9% before and 13.4 +/- 2.5% after nitroglycerin. Changes in the lateral chords paralleled changes in the central chords in the three studies. Nonischemic zone improvement after nitroglycerin in all three studies. Global ejection fraction improved and end-diastolic and end-systolic volumes decreased in all three studies after nitroglycerin. These data indicate that after acute myocardial infarction, there is a significant reduction in hemiaxis shortening in the central and lateral chords that remains essentially unchanged over 4-6 weeks. However, the asynergic ischemic area improves considerably after nitroglycerin within 24 hours and 5-7 days, but fails to improve after 6 weeks.

Nuclear cardiology. I. Radionuclide angiographic assessment of left ventricular contraction: uses, limitations and future directions

Radionuclide angiography has been increasingly utilized to evaluate left ventricular function in a wide variety of disease states. Comparison with contrast ventriculography has shown that radionuclide angiography is an accurate means of determining global ejection fraction. Moreover, studies have shown that this technique is of particular value in detecting the presence and severity of regional asynergy as, for example, in the delineation of a discrete aneurysm versus global asynergy as the cause of congestive heart failure. The relative ease of repetitive examinations permits evaluation of left ventricular function under different conditions. Thus, radionuclide angiography is being increasingly used as a prognostic and therapeutic guide. In addition, it can be used during an acute intervention--for example, with administration of nitroglycerin to detect reversible asynergy or, as recently demonstrated by several groups, during exercise as a relatively sensitive and specific means to detect coronary heart disease.

Of linens and laces--the eighth anniversary of the gated blood pool scan

Evaluation of ventricular performance is essential in the diagnosis and long-term management of patients with heart disease. This can be most easily performed clinically using simple tools. When more definitive objective assessment of cardiac function is indicated, the equilibrium gated blood pool study provides reliable angiographic evaluation of the heart. It will continue as a mainstay in the armamentarium of cardiology.

Instrumentation and data processing in cardiovascular nuclear medicine: evaluation of ventricular function

Cardiovascular nuclear medicine encompasses a variety of clinical procedures. Some of these procedures place demands on the imaging and data processing equipment that far exceeds those associated with other nuclear medicine procedures. This paper is devoted to an evaluation of the imaging and data processing requirements for two of the more demanding studies in cardiovascular nuclear medicine--first transit and gated equilibrium measurement of ventricular function. Imaging instrumentation and collimation, computer system hardware, and computer acquisition and analysis software are each treated as they apply to these procedures.

Regional ejection fraction: a quantative radionuclide index of regional left ventricular performance

Radionuclide measurements of regional left ventricular ejection fraction were evaluated as a quantitative index of regional left ventricular function. Left ventricular regional ejection fractions were derived from background-corrected, time-activity curves in 43 patients assessed by both gated equilibrium radionuclide angiocardiography and left ventricular contrast angiography. From a single, modified left anterior oblique projection, the regional change in background corrected counts was determined in each of three anatomic regions. The normal range for regional radionuclide ejection fraction was determined in 10 patients with normal contrast ventriculograms and without obstructive coronary artery disease at coronary arteriography. Regional ejection fraction was compared with percent segmental axis shortening and extent of akinetic segments in corresponding regions of the contrast ventriculogram. Radionuclide and roentgenographic methods were in agreement as to the presence or absence of abnormal wall motion in 83 of 99 left ventricular regions (84%) in 33 patients evaluated prospectively. Comparison of regional ejection fraction demonstrated significant differences between regions with roentgenographically determined normokinesis (75 +/- 3%, mean +/- SEM), hypokinesis (44 +/- 3%, p less than 0.0005) and akinesis (24 +/- 5%, p less than 0.005). We conclude that the left ventricular regional ejection provides a reliable quantitative assessment of regional left ventricular performance.

Afterload reduction and cardiac performance. Physiologic basis of systemic vasodilators as a new approach in treatment of congestive heart failure

Digitalis and diuretics constitute conventional therapy of congestive heart failure, but systemic vasodilators offer an innovative approach in acute and chronic heart failure of decreasing increased left ventricular systolic wall tension (ventricular afterload) by reducing aortic impedance and/or by reducing cardiac venous return. Thus, vasodilators increase cardiac output (CO) by diminishing peripheral vascular resistance (PVR) and/or decrease increased left ventricular end-diastolic pressure (LVEDP) (ventricular preload) by diminishing venous tone. Concomitantly, there is reduction of myocardial oxygen demand, thereby reliably reducing angina pectoris in coronary disease, and potentially limiting infarct size and ischemia provided systemic arterial pressure remains normal. The vasodilators produce disparate modifications of cardiac function depending upon their differing alterations of preload versus impedance: nitrates principally cause venodilation (decrease LVEDP); nitroprusside, phentolamine and prazosin produce balanced arterial and venous dilation (decrease LVEDP and increase CO) provided left ventricular filling pressure is maintained at the upper limit of normal; whereas hydralazine predominantly effects arteriolar dilation (increases CO). With depressed CO plus highly increased LVEDP and increased PVR, nitrates also induce some increase of CO by reducing PVR. Combined nitroprusside and dopamine synergistically enhance CO and decrease LVEDP. Mechanical counterpulsation aids nitroprusside in acute myocardial infarction. The 30-minute venodilator action of sublingual nitroglycerin is extended for 4 to 6 hours by cutaneous nitroglycerin ointment, by sublingual and oral isosorbide dintrate, and by oral pentaerythritol tetranitrate and sustained-release nitroglycerin capsules. Ambulatory oral vasodilator therapy is provided by long-acting nitrates (relieve pulmonary congestion); hydralazine (improves fatigue); prazosin alone, combined nitrate-hydralazine combined prazosin-hydralazine (improve both dyspnea and fatigue).

Nitroglycerin and nitrate esters

The expanding applications of nitroglycerin and nitrate esters--in congestive heart failure, in the reduction of infarct size in myocardial infarction and in the long-term prophylaxis of angina--have enhanced the clinical importance of these drugs. This article reviews some of the significant recent investigations of the nitrates and makes specific recommendations regarding clinical use.

Effect of nitroglycerin on exercise-induced abnormalities of left ventricular regional function and ejection fraction in coronary artery disease. Assessment by radionuclide clineagiography in symptomatic and asymptomatic patients

The effects of nitroglycerin (TNG) on exercise-induced abnormalities of left ventricular wall motion and ejection fraction are unknown in symptomatic and asymptomatic patients with coronary artery disease (CAD). In the present investigation radionuclide cineangiographic studies were performed in 47 patients with CAD (14 without angina during exercise) and in 25 normal subjects. All CAD patients, including those without symptoms, demonstrated regional wall motion abnormalities during exercise. In all patients, ejection fraction (EF) also responded abnormally to exercise: EF decreased from 48% at rest to 36% during exercise (P less than 0.001). EF increased in all normal subjects from an average of 58% at rest to 71% during exercise (P less than 0.001). In all CAD patients TNG reduced exercise-induced regional wall abnormalities and increased EF attained during exercise from an average of 36 to 48% (P less than 0.001). EF in normal subjects was unchanged by TNG. Thus, exercise can cause abnormalities in left ventricular regional function and ejection fraction in patients with or without symptoms; these abnormalities can be mitigated by prophylactic TNG.

Evaluation of left ventricular function (ejection fraction and segmental wall motion) by single pass radioisotope angiography

Changes in ejection fraction (EF) and segmental wall motion (SWM) have been shown to be sensitive indicators of left ventricular (LV) function. This information is only obtainable by contrast angiography or gated blood pool scans. Gated studies assume a fixed geometry for the LV for EF determinations, are lengthy and limited primarily to the LAO projection. We correlated contrast and Tc-99m pertechnetate angiograms by singl pass radioisotope angiography (immediately preceding the contrast study) in 12 patients. EF was calculated from the LV time/activity curve and values ranged from .21 to .72. Angiographic correlation yielded r = 0.97. Regional LV wall motion was evaluated by dividing a summated cardiac cycle into 16 frames and dynamically and sequentially displaying these frames. Regional wall motion evaluation of four LV quadrants correlated well with angiography (r = 0.97). For quantitation these images were divided into four anterior and four inferior segments and the areas of respective segments were compared and expressed as a shortening fraction. SWM compared favorably with angiographic determinations (r ranged from 0.70 to 0.99). Thus, single pass radioisotopic determinations of EF and SWM in the RAO projection correlated well with the angiographic values and provide essential quantitative information of LV function otherwise unobtainable at the bedside.

Radionuclide cinecardiography using minicomputer generated sequential gated images

Images

Noninvasive assessment of cardiac function and ventricular dyssynergy by precordial Q wave mapping in anterior myocardial infarction

To determine whether multiple lead precordial electrocardiographic recordings offer an improved index for noninvasive estimation of left ventricular hemodynamic function and segmental dyssynergy, precordial mapping was performed in patients with anterior myocardial infarction, and the number of pathologic Q waves (greater than or equal to 0.04 sec) was counted (Q-Index). Left ventricular function was determined by cardiac catheterization and angiography and correlated with the Q-Index. The Q-Index correlated well with dyssynergy extent (r = 0.84) and inversely with ejection fraction (r= -0.87), stroke work index (r = -0.79) and cardiac index (r = =0.66). Three patient groups were defined by Q-Index; group I, 0.04 sec Q complexes less than 15; group II, 15-25; group III, 26-35. Q-Index related closely to functional classification and survival (mean follow-up 12.2 months): group I, 91%; group II, 81%; group III, 40%. Thus 35-lead precordial Q wave mapping with determination of total number of pathologic Q waves permits practical, atraumatic assessment of hemodynamic and functional status and allows prediction of survival in acute and chronic anterior myocardial infarction.

Radiocardiography in clinical cardiology

Quantitative radiocardiography provides a variety of noninvasive measurements of value in cardiology. A gamma camera and computer processing are required for most of these measurements. The advantages of ease, economy, and safety of these procedures are, in part, offset by the complexity of as yet unstandaridized methods and incomplete validation of results. The expansion of these techniques will inevitably be rapid. Their careful performance requires, for the moment, a major and perhaps dedicated effort by at least one member of the professional team, if the pitfalls that lead to unrecognized error are to be avoided. We may anticipate more automated and reliable results with increased experience and validation.