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Biomedical subjects

R H Helfant

Publications and source records attributed to R H Helfant.

At least 91 records · Page 5Linked to original sources
PubMed1982

Contrasting ischemic contraction patterns by zone and layer in canine myocardium.

The effect of graded coronary occlusion on myocardial shortening in different zones of the left ventricle is not clear. Therefore, in 15 dogs ultrasonic crystals were used to evaluate the effect of graded coronary occlusion on subendocardial and subepicardial contraction in both the left anterior descending coronary artery (LAD) and left circumflex coronary artery (Circ) distributions. Subepicardial shortening was evaluated along both the long and short axes. In the LAD zones, segment shortening decreased in parallel in the subendocardium and subepicardium. In the circumflex zone subendocardial and subepicardial long axis shortening fell off in parallel, while subepicardial short axis shortening fell off more rapidly. Thus there is a close relationship between endocardial and epicardial segment shortening following graded coronary occlusion. In the circumflex zone, however, fiber orientation may affect the measurement of segment motion.

Animals↗
PubMed1982

The effects of nifedipine on myocardial blood flow and contraction during ischemia in the dog.

Nifedipine has been proposed as an agent to preserve viability and function of ischemic myocardium. We studied 23 open-chest dogs that underwent carotid-to-left anterior coronary artery perfusion with flow probe and perfusion pressure monitoring. Segment length was measured with ultrasonic crystals in the ischemic and nonischemic endocardium. Myocardial blood flow was measured with radioactive microspheres. Partial coronary occlusion was performed to 25 mm Hg diastolic perfusion pressure. Ten dogs received intracoronary nifedipine, 10 micrograms, and 13 dogs received i.v. nifedipine, 3 micrograms/kg/min. Nifedipine resulted in an increase in segmental shortening in both groups, but nonischemic zone shortening did not change in either group. Nifedipine did not affect myocardial blood flow in the ischemic zone, but increased flow in the nonischemic zone in the group that received i.v. nifedipine. Thus, nifedipine appears to have a direct beneficial effect on ischemic myocardium.

Animals↗
PubMed1982

Effects of digitalis on subendocardial and subepicardial dysfunction during acute ischemia.

The effects of digitalis (ouabain infusion, priming dose of 10 micrograms/kg/min followed by 2.0 micrograms/kg/min) on subepicardial and subendocardial ischemic dysfunction during partial occlusion (59.4% reduction in coronary flow) and total coronary occlusion were evaluated in 14 dogs using pairs of ultrasonic crystals implanted in the epicardial and endocardial layers. After 30 minutes of partial coronary occlusion, systolic shortening in the ischemic zone decreased from 12.4 +/- 2.9% to -0.4 +/- 0.9% (p less than 0.001) in the epicardium and from 18.9 +/- 3.1% to -1.0 +/- 1.1% (p less than 0.001) in the endocardium. Ouabain infusion increased the systolic shortening from -0.4 +/- 0.9% to 10.6 +/- 3.1% (p less than 0.001) in the epicardium and from -1.0 +/- 1.1% to 17.2 +/- 3.4% (p less than 0.001) in the endocardium. The end-diastolic length did not change. In contrast, after 30 minutes of total coronary occlusion, systolic shortening in both epicardial and endocardial layers was replaced by systolic lengthening and remained unaffected by ouabain infusion in both layers. Systolic shortening in the nonischemic epicardial and endocardial layers increased consistently. We conclude that ouabain improves the contractile function of both ischemic epicardial and endocardial layers layers after partial coronary occlusion and does not worsen subendocardial ischemic dysfunction. After total coronary occlusion, however, the contraction of the ischemic zone is unaffected by ouabain.

Animals↗
PubMed1981

Effects of isolated interventricular septal ischemia on global and segmental function of the canine right and left ventricle.

The effects of isolated septal artery ligation wee studied in 17 dogs. Contraction of the interventricular septum (IVS) and the free walls of both ventricles was measured by implanting ultrasonic crystals. Global ventricular function was assessed by Starling function curves. Following septal artery ligation, IVS shortening was immediately replaced by systolic lengthening. Thirty minutes after septal artery ligation, the right ventricular (RV) stroke work (SW) was significantly depressed at end-diastolic pressure (EDP) of 8 and 8.5 mm Hg from control values of 7.6 +/- 0.4 and 8.6 +/- 0.6 gmM to 6.7 +/- 0.4 and 7.4 +/- 0.5gmM respectively. However, LVSW after septal artery ligation was similar to control values for EDP from 5 to 19 mm Hg. These changes were associated with unchanged RV free wall movement of 21 +/- 3% in the inflow region and 23 +/- 5% in the outflow region. LV free wall systolic shortening following septal artery ligation increased by 16 +/- 3%. It is concluded that canine septal artery ligation causes global dysfunction of the RV but not of the LV.

Animals↗
PubMed1981

Differential effects of Renografin-76 on the ischemic and nonischemic myocardium.

The effects of intracoronary diatrizoate meglumine and diatrizoate sodium (Renografin-76) on regional contraction were examined in the normal coronary circulation and during partial (50 percent) coronary occlusion in 11 dogs using strain and length gauges. Intracoronary injections of Renografin-76 (1.5 cc) (1.690 mosM/liter; 0.19 mEq Na/ml), equiosmolar dextrose solution and 0.19 mEq Na+/ml saline solution were made randomly. Renografin-76 caused a decrease in preejection tension to 87.4 +/- 4.3 percent (p less than 0.025), total tension to 74.6 +/- 3.3 percent (p less than 0.01) and ejection tension to 11.9 +/- 12.6 percent (p less than 0.001) of control value. Segment length increased to 106.7 +/- 7.3 percent of control value. These changes lasted only 12 +/- 2 (range 5 to 20) seconds (mean +/- standard error of the mean). During partial coronary occlusion and after injection of Renografin-76, preejection tension decreased from 91.7 +/- 6.3 to 53.8 +/- 3.9 percent (p less than 0.01), total tension from 89.9 +/- 5.0 to 59.7 +/- 3.5 percent (p less than 0.01) and ejection tension from 22.8 +/- 8.1 to 17.8 +/- 10.9 percent, whereas segment length increased from 112.7 +/- 3.7 to 130.7 +/- 4.6 percent (p less than 0.01) of control value. In contrast to findings in the normal coronary circulation, tension and length changes lasted 54 +/- 16 (range 15 to 180) seconds (p less than 0.05). The hyperemic response during normal coronary circulation was completely abolished during partial coronary occlusion. Prior administration of nitroglycerin did not shorten the duration of the myocardial depressant effects of Renografin. Injections of equiosmolar dextrose or saline solution produced qualitatively similar but quantitatively less marked changes. Thus, intracoronary Renografin-76 has an accentuated and prolonged depressant effect on the ischemic as compared with the normally perfused myocardium; this effect is not solely due to its hyperosmolarity or sodium concentration.

Animals↗
PubMed1981

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.

Acute Disease↗
PubMed1981

Interventricular septal motion: biventricular angiographic assessment of its relative contribution to left and right ventricular contraction.

The interventricular septum (IVS) has conventionally been regarded as a functional part of the left ventricle (LV). To determine its normal range of motion, simultaneous biventricular cineangiograms (60 frames/sec) were performed (60 degrees left anterior oblique) in nine subjects without coronary or other heart disease. Arrhythmias were avoided by using a specially designed right ventricular (RV) angiographic catheter. IVS motion was studied qualitatively by three observers and quantitatively by superimposing end-systolic and diastolic frames using intra- and extracardiac reference points. Two transverse chords that trisected the end-systolic length of the IVS were drawn to quantitate IVS, LV and RV free wall motion. Qualitatively, the IVS thickened toward both RV and LV cavities as a result of shortening on its longitudinal axis. LV motion was 39.9 +/- 7.2% on the transverse axis, of which 31.2 +/- 5.2% was contributed by the LV free wall and 8.5 +/- 2.1% by IVS. RV transverse axis motion was 36.9 +/- 3.7%, of which 28.6 +/- 2.1% was contributed by the RV free wall and 8.3 +/- 2.3% by IVS motion. There was no difference between IVS motion toward the LV and that toward the RV. The IVS longitudinal axis shortened by 17.4 +/- 2.8% (p less than 0.001). The mean systolic IVS thickness increased symmetrically from 7.43 +/- 0.55 mm to 12.49 +/- 0.39 mm (p less than 0.001). In brief, the IVS thickens on its transverse axis and shortens on its longitudinal axis, contributing equally to RV and LV function.

Adult↗
PubMed1981

The relationship between myocardial blood flow and contraction by myocardial layer in the canine left ventricle during ischemia.

We investigated the relationship between regional myocardial blood flow (MBF) and segmental shortening in 17 open-chest dogs. The left anterior descending coronary artery was cannulated and perfused from the left carotid while measuring perfusion pressure. Graded occlusion was produced by a screw clamp. Extent of occlusion was monitored by perfusion pressure. Percent systolic shortening (% delta L) was measured using ultrasonic crystals implanted in normal and ischemic endocardium and ischemic epicardium. MBF was measured in ischemic and normal endocardium and epicardium with tracer microspheres. Dogs underwent 1 to 4 grades of coronary stenosis. Myocardial blood flow both to endocardium and epicardium was found to be linearly related to diastolic perfusion pressure below 50 mmHg (r = 0.803 and 0.748, respectively). Normalized % delta L (N% delta L) was best related to fraction normal zone MBF in the endocardium by the sigmoidal equation, N% delta L = e9.01 MBF-4.03/1 + e9.01 MBF-4.03. % delta L was only weakly related to myocardial blood flow in the epicardium (r = 0.584), and, in four dogs, % delta L was zero in the epicardium despite normal regional blood flow. However, % delta L in the epicardium was linearly related to % delta L in the endocardium (r = 0.78). Thus, endocardial wall motion is related to MBF by a sigmoidal relationship while epicardial wall motion is tethered to endocardial wall motion.

Animals↗
PubMed1981

Variable effect of nifedipine on myocardial blood flow at three grades of coronary occlusion in the dog.

The effect of nifedipine on myocardial blood flow at various grades of coronary stenosis is unknown, Thus 22 open-chest dogs underwent carotid to left anterior descending perfusion with flow and perfusion pressure monitoring. Grades of coronary occlusion were defined by minimum diastolic perfusion pressure. six dogs (group 1) underwent moderate occlusion to 50 to 55 mm Hg diastolic perfusion pressure; (group 2), severe occlusion to 40 mm Hg perfusion pressure; and six (group 3), more severe occlusion at 25 mm Hg. Regional myocardial blood flow was measured with radioactive microspheres before and after the intracoronary injection of 10 microgram of nifedipine. In group 1, nifedipine induced epicardial hyperemia and little change in endocardial flow in the ischemic zone. In group 2, nifedipine induced epicardial hyperemia from 1.06 to 1.39 mg/g per min, but endocardial flow decreased from 0.70 to 0.60 ml/g per min. In group 3, there was no change in blood flow. Thus the effect of nifedipine on myocardial blood flow depends on the extent of occlusion. Furthermore for certain degrees of occlusion, redistribution of blood flow from endocardium to epicardium has been shown to occur.

Animals↗
PubMed1981

Regional coronary flow and contraction after partial coronary obstruction. Comparative effects of nitroglycerin and nitroprusside.

Following partial coronary occlusion, the comparative effects of administration of nitroglycerin and nitroprusside on aortic perfusion pressure, coronary flow, local tendon, and segmental length were assessed. Partial coronary occlusion decreased coronary flow from 78.9 +/- 5.0 ml/gm to 40.6 +/- 2.6 ml/100 gm and total tension to 76.9 +/- 5.6 percent of the control value. Nitroglycerin and nitroprusside improved total tension to a similar degree with a reduction of either 10 or 20 mm Hg in systolic pressure; however, when systolic pressure was reduced by 30 mm Hg, nitroglycerin decreased total tension slightly but insignificantly, while nitroprusside significantly decreased ischemic zone tension. Changes in segment length shortening paralleled changes in total tension. Thus, in the presence of partial coronary occlusion, both nitroglycerin and nitroprusside similarly affect coronary blood flow, total tension, and systolic shortening at a decrease of 10 and 20 mm Hg in systolic pressure; however, at a decrease of 30 mm Hg, both nitroglycerin and nitroprusside decrease total tension and systolic shortening.

Animals↗
PubMed1981

Efficacy of nifedipine in rest angina refractory to propranolol and nitrates in patients with obstructive coronary artery disease.

Nineteen patients with recurrent rest angina were given oral nifedipine. All patients had chest discomfort refractory to propranolol and oral or topical nitrates given to tolerance. The addition of nifedipine, 30 to 120 mg daily, abolished rest angina in 14 patients, decreased its frequency in two, and had no effect in three patients. Five of seven patients on long-term nifedipine (mean, 6.2 +/- 3.4 months) remained free of rest pain. Of seven patients who had their nifedipine dose decreased or discontinued, five had recurrent rest angina. Of the 19 patients, 16 had coronary angiography. Five had three- vessel obstructive disease (greater than 75% lesion), six had two-vessel obstructive disease, and five had one-vessel obstructive disease. The remaining three unstudied patients had pathologic Q waves in the ECG. Thus nifedipine appears to be an efficacious agent in the treatment of refractory rest angina in patients with obstructive coronary artery disease.

Adult↗
PubMed1981

Effect of progressive pressure reduction with nitroprusside on acute myocardial infarction in humans. Determination of optimal afterload.

The effect of nitroprusside-induced progressive systemic pressure reduction on segmental function in patients with acute myocardial infarction is unclear. In 15 patients control radionuclide angiograms were obtained at control within 24 hours of the onset of chest pain and during the administration of intravenous nitroprusside. The initial study showed a significant reduction in hemiaxial shortening in the zone of myocardial infarction. With nitroprusside, systolic pressure was decreased from a mean of 133 mm Hg to an intermediate pressure of 116 mm Hg (p less than 0.001). At this pressure central chord hemiaxial shortening increased in eight of 15 zones with an average increase from 10.1% to 27.8% (p less than 0.006). After further reduction in pressure to 87.1 mm Hg, an additional five of the seven remaining zones of acute infarction improved. However, of the eight zones that improved initially, four deteriorated at the lowest pressure. Similar changes were seen in the lateral chords. Thus, afterload reduction can improve hemiaxial shortening of the infarct zone. However, the degree of reduction in systemic pressure must be individualized to avoid adverse effects of an excessive decrease in perfusion pressure.

Adult↗
PubMed1980

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.

Arrhythmias, Cardiac↗
PubMed1980

Nuclear cardiology. II. The role of myocardial perfusion imaging using thallium-201 in diagnosis of coronary heart disease.

Since its introduction, thallium-201 has become the agent of choice in the clinical assessment of relative myocardial perfusion. Extensive evaluation has shown that it is of particular value in the diagnosis of coronary heart disease in patients with baseline S-T segment abnormalities or an inadequate heart rate response resulting in an inconclusive exercise electrocardiographic response. In addition, thallium-201 imaging is of value in the patient with a suspected false positive stress test; however, the definite incidence of false negative studies in patients with coronary heart disease tempers complete reliance on this approach. In the patient with a diagnostic exercise electrocardiographic stress test, thallium-201 provides limited additional information. Moreover, current techniques of analysis do not permit assessment of the number of coronary arteries with obstructive lesions. In the setting of acute myocardial ischemia, the role of thallium-201 is less clear. In acute myocardial infarction, the significant incidence of false negative responses combined with a multiplicity of potential causes of resting defects including severe but chronic coronary disease or unstable angina limits its diagnostic value.

Acute Disease↗
PubMed1979

Coronary spasm.

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Angina Pectoris, Variant↗
PubMed1979

Extent and severity of coronary heart disease. Determinations by thallous chloride Tl 201 myocardial perfusion scanning and comparison with stress electrocardiography.

Rest and exercise ECGs are the most widely used "noninvasive" tests for detecting coronary heart disease, but their sensitivity and specificity are suboptimal. Therefore, the diagnostic value of myocardial perfusion scanning using thallous chloride Tl 201 during rest and stress electrocardiography was examined in 95 patients with a chest discomfort syndrome. Overall, thallous chloride Tl 201 perfusion scanning had a sensitivity of 75% and a specificity of 91% for coronary heart disease compared with 56% sensitivity and 86% specificity with exercise-induced ST segment depression on the ECG. Combining rest and stress ECGs resulted in a sensitivity of 71%. In patients with coronary heart disease, perfusion scanning had a sensitivity of 93% for asynergy compared with 58% for exercise-induced ECG ST depression. Rest and stress myocardial perfusion scanning with thallous chloride Tl 201 provides improved sensitivity with good specificity in the diagnosis of coronary heart disease compared with exercise electrocardiography alone.

Arrhythmias, Cardiac↗