Regional left ventricular wall dynamics before and after sublingual administration of nitroglycerin

Earl Wood--a research career noted for development of novel instruments driven by the power of the indicator dilution concept

During World War 2, Earl Wood was charged with elucidating the biomedical factors in acceleration-induced loss of consciousness experienced by pilots in high-performance aircraft. For this, he developed devices for measurement and recording of blood pressure and tissue blood content. Those data lead to the design and fabrication of successful countermeasures to acceleration-induced loss of consciousness with an inflatable "G-suit" and "M1" breath-holding maneuver. After World War 2, he utilized and modified these instruments and made use of indicator dilution techniques by continuous intracardiac blood sampling to greatly increase the specificity and sensitivity of diagnosis of intracardiac anatomic and functional abnormalities in patients with congenital heart disease. This contributed to the greatly increased success rate of open-heart surgery in the 1950s. In the 1960s, he built on the then recently available video-coupled electronic X-ray image intensifier to develop X-ray fluoroscopy-based recording of indicator dilution signals in all cardiac chambers and surrounding great vessels without the need for placing catheter tips at those locations for blood sampling. However, these blood flow-related data were of limited value, as they were not measured concurrent with myocardial functional demand for perfusion. In the 1970s, he overcame this limitation by developing a high-speed multislice X-ray imaging scanner to provide tomographic images of concurrent dynamic cardiac anatomy and the indicator dilution-based estimates of blood flow distributions. On his retirement at age 70 in 1982, he had accomplished his 2 decade-old goal of the ability to make accurate concurrent, minimally invasive, and indicator dilution-based measurement of cardiovascular structure to function relationships.

Measurements of the effects of percutaneous nitroglycerin on left ventricular performance in patients with coronary artery disease with a cardiac probe

Left ventricular function was measured after percutaneous nitroglycerin in ten patients with coronary artery disease under double blind random control. The elevation of LVEF after percutaneous nitroglycerin paste (containing 10 mg nitroglycerin) was 8.3% +/- 1.3% (P less than 0.001) at 30 min, 8.5% +/- 1.8% (P less than 0.001) at 60 min, 10.1% +/- 1.8% (P less than 0.001) at 90 min and 8.7% +/- 2.2% (P less than 0.01) at 120 min respectively, but the change of LVEF after nitroglycerin ointment (containing 5 mg nitroglycerin) was not significant. The elevation of ER and RCO after nitroglycerin paste were 0.448 +/- 0.088 (EDV/s) (P less than 0.001), 6.73 +/- 1.47 (EDV/s) (P less than 0.01) at 30 min, 0.376 +/- 0.078 (P less than 0.001), 6.64 +/- 1.36 (P less than 0.001) at 60 min, 0.456 +/- 0.089 (P less than 0.001), 8.02 +/- 2.11 (P less than 0.001) at 90 min and 0.358 +/- 0.076 (P less than 0.01), 6.18 +/- 2.05 (P less than 0.01) respectively. It was demonstrated that percutaneous nitroglycerin paste (10 mg nitroglycerin) can improve the left ventricular function of patients with coronary artery disease.

Influence of sublingual nitroglycerin on the digital circulation of man

By means of the digital rheoplethysmographic (RPG) method, the effect of sublingually administered nitroglycerin (NTG), 1/200 gr (0.3 mg), on the digital circulation was studied in 17 normal subjects and 5 patients with ischemic heart disease and angina pectoris. NTG produced dilatation of all digital vessels, reflected especially by increases in total digital volume. NTG produced marked changes in the dicrotic notch of the pulse wave, noted also in inflow volume curves but not in outflow volume curves. The dicrotic notch was displaced later on the descending limb of the digital pulse wave and became deeper and more prominent after NTG. It is suggested that NTG produces disproportionate dilatation of the arterial system, having its greatest effect on arteries near the heart, including the coronaries and great vessels branching off the aorta, and on left intraventricular cavity pressure. This greater regional vasodilatation of vessels near the heart could delay closure of the aortic valve, producing a delayed and prominent dicrotic notch of the pulse wave.

Left ventricular dyskinesia reversed by intravenous nitroglycerin: a manifestation of silent myocardial ischemia

Patients with coronary artery disease (CAD) frequently have left ventricular (LV) wall motion abnormalities in the absence of symptoms. Thirty-one patients with such LV wall motion abnormalities in the absence of symptoms participated in a study of the response of these abnormalities to ascending doses of intravenous nitroglycerin (NTG). In a subgroup of 20 patients the relation between the location of LV wall motion abnormalities and the presence or absence of significant CAD (greater than or equal to 50% diameter reduction), in the vessel supplying the LV region, was assessed. Wall motion improved after intravenous NTG; the ejection fraction increased by 3.7% (mean p less than 0.05) and by 9.4% in the 19 patients who responded. There was no significant increase in heart rate; both LV systolic and end-diastolic pressures decreased minimally (12.5 and 3.5 mm Hg, respectively, p less than 0.05). The ejection fraction response was observed with NTG doses less than or equal to 200 micrograms and no dose-response relation was apparent. In the subgroup subjected to regional wall motion analysis, the presence of dyskinesia was significantly (p = 0.007) associated with the presence of important CAD in a vessel supplying that region. Further, the fact that wall motion improvement after NTG was significantly (p = 0.002) associated supports the concept that silent ischemia results in LV regional wall motion abnormalities, which can be reversed with low dose intravenous NTG.

Paradoxical deterioration of left ventricular asynergy after administration of nitroglycerin

The effects of nitroglycerin on segmental asynergy were studied by 2-dimensional echocardiography. Forty-five patients with coronary artery disease and segmental wall motion abnormality at rest were examined, 31 with Q-wave and 14 with only ST-T abnormalities. Left ventricular (LV) echocardiograms were recorded from the LV apex in 4 planes, obtained by systematically rotating the transducer at 45 degrees intervals around the mitral office, using a mechanical device. Sixteen LV segments were analyzed in each patient on real-time display by 2 observers independently. The wall motion analysis was classified as normal, hypokinetic, akinetic or dyskinetic. Of 720 segments, 596 were agreed on by 2 observers in the assessment of wall motion before and after administration of nitroglycerin: 334 segments (56%) showed no change in wall motion, 206 (35%) showed improvement of wall motion and 56 (9%) showed worsening of myocardial asynergy after nitroglycerin. These data suggest that administration of nitroglycerin may result in unexpected worsening of segmental asynergy. This may be secondary to an adverse effect of a decrease in perfusion pressure in critically occluded arteries or may represent a coronary steal phenomenon.

Three-dimensional analysis of regional myocardial function in response to nitroglycerin in patients with coronary artery disease

Biplane cineventriculography was performed at rest and after sublingual nitroglycerin in 13 patients with coronary artery disease. In six patients (responders), there was a significant increase in ejection fraction [40 +/- 5 to 52 +/- 4% (p less than 0.001)], while in the other seven (nonresponders), there was no alteration in ejection fraction. To evaluate the extent of regional myocardial response to nitroglycerin, the contractile pattern of the regional myocardium over the entire ventricular surface was analyzed using a computer-generated three-dimensional model. The spatial coordinates that define the elliptic ventricular surface on a given horizontal plane cross section of the chamber were determined by four counter values in the two orthogonal silhouettes. Then, 32 points at equal angles around the center of gravity of the end-diastolic cavity were generated to form the border image. Repetition of this process for 16 successive cross sections allowed for reconstruction of the ventricular surface by the sequence of 32 X 16 (512) points. The regional wall motion was expressed as the percent change of the radial length, drawn from the center of gravity to each surface point. There was significant heterogeneity in regional response to nitroglycerin. In the responders, the normally contracting area was significantly increased (from 16.5 +/- 16.0 to 36.2 +/- 14.9% of the total surface area, p less than 0.001), largely mediated by the greater improvement in segmental shortening of each graded contractile pattern relative to its deterioration. In the nonresponders, a lessening of the severe dysfunction of the given area was associated with significant deterioration of segmental shortening of the other normally contracting area (49.1 +/- 19.7% of the area with a contractile pattern of grade 5 had deteriorated, p less than 0.05). Thus, the ratio of the area with respective graded segmental shortening was virtually unchanged. These differences in response of the ischemic ventricle to nitroglycerin appeared to be related to the development of adequate coronary collateral vessels as well as to an interaction of changes in preload and afterload.

Clinical evaluation and application of cardiac laboratory high-definition video systems

This study evaluated a new high line rate (1,023-line) high band-width (10 MHz) system, compared it to our high-definition, 525-line video system, and compared both video systems to 35-mm cine angiography in 117 patients undergoing clinically indicated coronary angiography. The subjective image quality of the 1,023-line video system was not significantly better than that of the 525-line system. High line rate, high band-width systems may have theoretical advantages, but the increased noise level under clinical angiographic conditions reduces their diagnostic quality. Comparison between video (all modes) and cine images resulted in cine being rated as the best modality, but the differences were slight. Radiation levels required for video imaging, however, were significantly less than those required for cine recording. Current clinical and computer interactive uses of video systems in the cardiac laboratory are described. The eventual role and potential replacement of cine recording by video tape systems will depend on continued developments in video recording techniques.

Relation between functional response to nitroglycerin and extent of myocardial necrosis in dogs: mapping of the left ventricle by 2-dimensional echocardiography

The relation between functional response to brief nitroglycerin infusions and extent of myocardial damage was studied sequentially in closed-chest dogs with acute occlusion of the left anterior descending coronary artery. Two-dimensional echocardiography was used to derive segmental left ventricular (LV) function (systolic fractional area change and systolic wall thickening), and this function was compared with the extent of necrosis measured 5 hours after occlusion in equivalent segments of corresponding pathologic slabs. Two-dimensional echocardiographic study before the dogs were killed indicated that remote nonnecrotic segments always responded to nitroglycerin by significant augmentation of segmental LV function. Segments in which necrosis was less than 40% showed a significant nitroglycerin-induced potentiation in segmental LV function. In contrast, segments in which necrosis was greater than 60% had no potentiation with nitroglycerin. In those segments in which eventual necrosis was 60 to 80%, significant nitroglycerin-induced augmentation in segmental LV function was observed only before and 30 minutes after the coronary occlusion. When the degree of necrosis was greater than 80%, no significant potentiation of segmental LV function was observed even as early as 30 minutes after occlusion. Thus, the degree of nitroglycerin-induced potentiation of segmental cardiac function is closely associated with the extent of myocardial necrosis in the particular ventricular segment. Two-dimensional echocardiography coupled with a nitroglycerin potentiation test might be useful for assessment of the viability of ischemic myocardium.

Nitroglycerin intravenous infusion

The treatment of various cardiovascular problems with intravenous nitroglycerin is widely practiced though unapproved. The uses of iv nitroglycerin include improvement of the hemodynamics of left ventricular failure and cardiogenic shock associated with infarction, control of hypertension during coronary artery surgery, and possibly, reduction of acute myocardial infarct size. The popularity of this treatment in the absence of an FDA-approved commercial product has forced some hospitals to prepare the drug extemporaneously, and the advantages and disadvantages of preparation and storage techniques are presented.

Pharmacologic intervention in cardiovascular nuclear medicine procedures

Relevant questions in ischemic heart disease are (1) what is the ischemic threat? (2) What is the extent of ventricular dysfunction? (3) Is the observed dysfunction reversible? Exercise testing can help to identify the ischemic threat. Catheterization studies have shown that resting ventricular dysfunction can be reversed in some patients through pharmacologic or surgical intervention. However, improved ventricular performance in ischemic heart disease may be achieved through a variety of mechanisms. Insight into all components of cardiac performance (regional and global contractillity, preload, afterload, and heart rate) and myocardial perfusion may be required to adequately describe the influence of intervention. Exercise radionuclide ventriculographic studies have demonstrated that stress-induced ventricular dysfunction can be reversed through surgical and pharmacologic intervention. Studies at rest have demonstrated that radionuclide techniques can detect drug-induced changes in ventricular performance in groups of patients. The challenge to cardiovascular nuclear medicine is the prospective identification of patients who would benefit most from aggressive intervention aimed at preventing or reversing ischemic ventricular dysfunction.

Effects of nitroglycerin on echocardiographic measurements of left ventricular wall thickness and regional myocardial performance during acute coronary ischemia

The effects of nitroglycerin on regional left ventricular performance, assessed by echocardiographic techniques, were investigated in anesthetized, open-chest dogs during acute myocardial ischemia. During transient occlusion of the left anterior descending coronary artery, there was end-diastolic thinning and marked reduction in systolic thickening in the central ischemic zone. Similar changes of lesser degree were noted in the border zone. The normal zone was unaffected. Infusion of nitroglycerin during ischemia in dosages of 2.5--50 microgram/kg/min reduced left ventricular end-diastolic pressure without changing the abnormalities of systolic wall thickening. Effects of bolus injections of 20 and 50 microgram/kg of nitroglycerin were similar, although this also lowered aortic pressure. In a subgroup of animals in which nitroglycerin infusion was unaccompanied by tachycardia, there was also no evidence that ischemic dysfunction was altered. We conclude that nitroglycerin does not improve regional myocardial performance in acutely ischemic canine myocardium. The decrease in preload is probably entirely due to the peripheral effects of the agent.

Improvement of myocardial perfusion and left ventricular function after coronary artery bypass grafting in patients with unstable angina

Changes in myocardial perfusion and left ventricular function were evaluated pre- and post-operatively (3--6 months) in 14 patients with unstable angina who underwent coronary artery bypass surgery. Perfusion was studied with intracoronary and intragraft injections of radiolabeled macroaggregated albumin particles. Of 20 abnormal perfusion areas identified preoperatively, 13 demonstrated improved perfusion post-operatively. Segmental analysis of the left ventriculogram demonstrated improved wall motion in 29 abnormally contracting segments; 18 normalized. Areas which showed improvement of left ventricular perfusion were invariably associated with improvement of left ventricular wall motion. Five patients showed improvement in perfusion and contraction in areas of apparent old myocardial infarction. Thirteen of the 14 patients had significantly less angina whether or not there was evidence of improved perfusion. However, only those patients who demonstrated improved perfusion had a significant improvement in their treadmill exercise tolerance postoperatively. Thus, patients with unstable angina have perfusion defects which may be reversed as a result of saphenous vein graft surgery. Reversal of these perfusion abnormalities results in improved left ventricular performance and better exercise tolerance postoperatively.

Relation between left coronary artery stenosis and regional left ventricular function

The effect of stenosis of the left main and proximal anterior descending coronary arteries on anterior left ventricular wall dynamics was investigated in 70 patients with ischemic heart disease by the use of roentgen videometric analysis of left ventricular angiograms. In all patients with ischemic heart disease, mean values for peak rate of systolic wall thickening and diastolic wall thinning were significantly smaller than normal (P less than 0.01). In patients without infarction, there was no correlation between peak rate of systolic anterior wall thickening and stenosis of the coronary artery supplying it, but there was a significant reduction in peak rate of diastolic wall thinning (P less than 0.01) in patients with stenosis greater than 90%; this difference was not apparent at any lower degree of stenosis. This population could not be recognized by any other parameter of global or regional ventricular function; thus, diastole is more sensitive to regional left ventricular dysfunction than systole.

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.

Regional myocardial wall thickening response to nitroglycerin. A predictor of myocardial response to aortocoronary bypass surgery

The peak rate of systolic wall thickening (p +/- dTw/dt) in regions of the left ventricle (LV) was determined preoperatively by biplane roentgen videometry in 18 patients before and after sublingual administration of nitroglycerin (NTG) and 3-23 months (median 12) after aortocoronary bypass surgery. The regional LV response to NTG was a reliable predictor for postoperative improvement in regional wall dynamics after successful aortocoronary bypass grafting. The ejection fraction response to NTG or surgery will not predict the regional myocardial response to NTG or surgery, nor will the regional response predict the global response. Subendocardial myocardial infarction is another cause of unimproved regional myocardial function after NTG and aortocoronary bypass surgery.

The similarity of changes in segmental contraction patterns induced by postextrasystolic potentiation and nitroglycerin

Despite a fundamental difference in their underlying mechanisms, both postextrasystolic potentiation (PESP) and administration of nitroglycerin (TNG) have been utilized to predict reversibility of abnormal segmental wall motion in patients with ischemic heart disease. To determine whether these interventions induce the same changes in segmental contraction pattern, we analyzed biplane ventriculograms of 14 patients who had an adequately visualized PESP beat on a basal ventriculogram as well as a post-TNG ventriculogram. Four segments in each plane were defined and the area ejection fraction of each segment was calculated for a basal sinus, PESP, and post-TNG beat. To correct for global differences in the response to PESP and TNG, we normalized each segmental ejection fraction (NSEF) by the ventricular ejection fraction for that beat and then compared the differences in NSEF from the basal value after PESP and TNG. Eleven patients demonstrated similar responses to both interventions. The three patients whose responses were discordant had elevated or unchanged left ventricular systolic or end-diastolic pressures at the time of the TNG ventriculogram. Our data suggest that, provided these pressures are lower than basal values at the time of the TNG ventriculogram, PESP and TNG will induce similar changes in segmental contraction patterns. Seven patients with similar responses had a PESP beat on their post-TNG ventriculogram. Changes in NSEF after PESP+TNG were identical to those after either intervention. This implies that the combination of interventions does not induce further changes in segmental contraction pattern beyond that produced by either intervention alone.

Regional and global myocardial effects of intravenous and sublingual nitroglycerin treatment after experimental acute coronary occlusion

The consequences of sublingual and intravenous nitroglycerin treatment after acute coronary occlusion were studied in 18 closed chest dogs. Intravenous (0.1 mg/min) or sublingual (0.4 mg/15 min) nitroglycerin therapy was instituted 1 hour after occlusion and the effects were observed over a period of 2 hours. Hemodynamics and global and regional cardiac function were measured in both the coronary occluded and nonoccluded segments of the left ventricle before and during coronary occlusion, and after administration of nitroglycerin. A similar nine dog control series was used to establish the significance of the measured effects of nitroglycerin. Intravenous nitroglycerin therapy after 1 hour of occlusion resulted in a marked increase in heart rate (37 +/- 12 [mean +/- standard error of the mean] percent), reduction of systolic blood pressure (9 +/- 3%), decrease in left ventricular end-diastolic and end-systolic volumes (32 +/- 5% and 34 +/- 5%), increase in coronary sinus flow (64 +/- 24%) and decrease in left ventricular stroke work (29 +/- 8%). Sublingually administered nitroglycerin produced similar trends but much less pronounced effects. However, intravenous or sublingual administration of nitroglycerin provided no improvement or caused further deterioration in ischemic region lactate extraction and potassium loss. The left ventricular ejection fraction, which was severly depressed after 1 hour of occlusion, changed minimally after administration of nitroglycerin, and there was no evidence of any correction of regional left ventricular akinesia or dyskinesia. Whereas mean systemic vascular resistance changed minimally as a result of nitroglycerin therapy, it increased 19 +/- 8% during a corresponding period of an untreated coronary occlusion series suggesting that nitroglycerin prevented an anticipated increase. Postocclusion S-T segment elevation in the electrocardiogram persisted after treatment. Our data corroborated that nitroglycerin reduced left ventricular volumes and increased coronary sinus flow; however, these improvements were accompanied by persisting metabolic and mechanical derangements in the ischemic region.