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Biomedical subjects

R H Helfant

Publications and source records attributed to R H Helfant.

At least 55 records · Page 3Linked to original sources
PubMed1986

Videodensitometric quantitation of aortic regurgitation by digital subtraction aortography using a computer-based method analyzing time-density curves.

To assess the clinical role of computer analysis of time-density curves in the evaluation of aortic regurgitation (AR), digital subtraction aortography (DSA) and cineaortography were performed sequentially in 17 patients with varying degrees of AR (1+ to 4+) and in 4 control patients. DSA was performed at a rate of 30 frames/s on a 512 X 512 X 8 bit pixel matrix using the same total volume and injection rate, but with half the amount of contrast agent as standard cineaortography. A 30 X 30 pixel area of interest was identified in the aorta above the valve plane and in the left ventricle where the AR stream was seen. The density of both areas of interest and the ratio of left ventricular/aortic area of interest density was calculated in each frame and then plotted vs time. The ratio at the end of injection (LVd/Aod) had an excellent correlation with cineaortography (chi 2 = 19, p less than 0.001), ranging from 0 to 0.2 in patients with no AR, 0.2 to 0.5 in those with 1+ AR, 0.5 to 0.7 in those with 2+ AR, 0.7 to 0.9 in those with 3+ AR and more than 0.9 in those with 4+ AR. Thus, quantitative assessment of AR by computer analysis of time-density curves derived from DSA is a new and objective technique with significant clinical potential.

Aortic Valve Insufficiency↗
PubMed1986

Multistage analysis of exercise radionuclide angiography in coronary artery disease.

The hypothesis that serial assessment of left ventricular function during exercise radionuclide angiography provides improved diagnostic criteria for coronary artery disease (CAD) was examined. Fifty-eight consecutive patients without previous myocardial infarction were prospectively scheduled for cardiac catheterization and multistage radionuclide angiographic exercise studies. Forty-one patients had significant CAD. The traditional criterion--failure to achieve a 5% increment in ejection fraction (EF) during exercise compared with the value at rest--had 85% sensitivity but only 41% specificity for CAD. In 12 patients, EF increased early in exercise by at least 4% and then decreased a mean of 7.5%, often with worsening regional wall motion. This "up-down" EF pattern was applied as a diagnostic test in the overall study group. Analysis of changes in EF from the maximal value achieved to that at the end of exercise resulted in criteria with greater sensitivity (p less than 0.0001) for CAD than analysis of changes from rest, with similar specificity. Regional wall motion abnormalities occurring during the first exercise stage resulted in 94% specificity for CAD (p = 0.05 vs end-stage analysis), although sensitivity was low. Analyzing the maximal EF during exercise results in improved sensitivity, while analyzing the early onset of regional dysfunction results in high specificity for CAD.

Adult↗
PubMed1986

Prognostic significance of severe narrowing of the proximal portion of the left anterior descending coronary artery.

To determine the prognostic importance of significant narrowings involving the proximal left anterior descending coronary artery (LAD), 866 medically treated patients with significant coronary artery disease (CAD) were followed after cardiac catheterization for a mean of 17 months (range 1 to 46). Coronary narrowings in all patients were evaluated based on site relative to large branches and on angiographic severity. Prognosis was best predicted by the presence of at least 70% diameter reductions in the LAD before the first 2 large branches (chi 2 = 16, p = 0.0001). At 3 years, there was a 94% cumulative survival rate in patients with less than 70% stenoses at this location, but an 82% survival rate in patients with 70% or more stenoses (p less than 0.0001). In addition, although the presence of proximal LAD narrowings was the best predictor of prognosis in patients with a low global ejection fraction, this was not so in patients with normal ejection fractions, as this subgroup had an excellent overall prognosis. Thus, the presence and severity of significant stenoses in the proximal LAD are stronger predictors of prognosis than stenoses elsewhere in the major coronary arteries. The presence of an angiographically significant narrowing in this anatomic location is highly correlated with an increased 1- to 3-year mortality rate.

Coronary Disease↗
PubMed1986

Hypokalemia and arrhythmias.

The focus of this article is hypokalemia, its electrophysiologic properties, and clinical arrhythmias. The effects of potassium on the electrophysiologic properties of the heart have been extensively studied and clearly are arrhythmogenic. Hypokalemia increases resting membrane potential and increases both the duration of the action potential and the duration of the refractory period, the latter to a greater degree than the former. This combination is conducive to the genesis of reentrant arrhythmias. Hypokalemia also increases threshold potential as well as automaticity, thus providing the context for automatic arrhythmias as well. Lastly, hypokalemia decreases conductivity, which also predisposes to arrhythmias of the reentrant type. The electrocardiographic criteria for hypokalemia include the presence of U waves greater than 1 mm and U waves larger than the T wave in the same lead (with associated ST-segment depression). Other criteria have been a T:U ratio of 1 or less and a U wave greater than 0.5 mm in electrocardiographic lead II or greater than 1.0 mm in lead V3. The relationship between hypokalemia and clinical arrhythmias has long been recognized. In 1949, Bellet et al reported extrasystoles with hypokalemic alkalosis that decreased with potassium administration. These observations were confirmed by several groups in the early 1950s. In 1953, Surawicz and Lepeschkin described a series of patients with hypokalemia and frequent junctional and ventricular premature beats; in all cases the arrhythmias disappeared with administration of potassium. These clinical observations were strengthened by the 1962 findings of Gettes et al, who employed microelectrode techniques to show that perfusion of low potassium solutions resulted in ventricular ectopic beats, ventricular tachycardia, and ventricular fibrillation. In more recent years, several studies have evaluated the relationship between potassium levels and arrhythmias in patients with and without hypertension who were receiving diuretic therapy. These studies have demonstrated that there is an increased incidence of ventricular arrhythmias associated with the hypokalemia induced by diuretic therapy, an observation with obvious clinical implications.

Action Potentials↗
PubMed1986

Rate of left ventricular functional recovery by radionuclide angiography after exercise in coronary artery disease.

To characterize determinants of the rate of recovery of left ventricular (LV) function after exercise-induced ischemia, sequential postexercise radionuclide angiography was performed prospectively in 38 consecutive patients with documented coronary artery disease (CAD). In each patient new or increased regional asynergy developed or absolute ejection fraction decreased at least 4% during exercise. Twenty patients showed immediate recovery of LV function after exercise (group 1) and 18 showed delayed recovery (group 2). Ejection fraction in the first postexercise period was significantly greater in group 1 (65 +/- 12%) than in group 2 (55 +/- 11%) (p less than 0.01). The mean number of coronary arteries with at least 70% diameter narrowing was greater in group 2 (2.7 +/- 0.5) than in group 1 (2.0 +/- 0.9) (p = 0.026); CAD score was also greater in group 2 than in group 1 (p = 0.005). The increase in LV end-diastolic volume from rest to end exercise was greater in group 2 than in group 1 (p = 0.005); neither the change in LV volume nor the change in heart rate or blood pressure after exercise separated the groups. The only independent predictor of the rate of functional recovery was the degree of exercise-induced regional myocardial asynergy (p less than 0.001). Thus, exercise radionuclide angiography in patients with CAD provides a model for evaluating postischemic myocardial function. Delayed functional recovery is associated with extensive exercise-induced regional asynergy as a result of severe CAD and is not primarily influenced by hemodynamic changes.

Adult↗
PubMed1986

Prospective evaluation of the severity of coronary artery disease with exercise radionuclide angiography and electrocardiography.

To evaluate the utility of exercise radionuclide angiography (RNA) and electrocardiography in assessing the severity of coronary artery disease (CAD), 185 patients undergoing coronary angiography were studied prospectively. To avoid work-up bias and to provide an appropriate control group, all patients were simultaneously scheduled for exercise RNA and electrocardiography and for coronary arteriography. All test results were interpreted blinded to other data. Of multiple exercise variables analyzed by stepwise linear discriminant analysis, the independent predictors of disease severity were exercise ejection fraction, ST segment change, and maximum heart rate. These three variables were used to create a set of four equations that determine probabilities of zero, one-, two-, or three-vessel disease (VD). The noninvasive estimate of number of VD in each patient was compared to the angiographic result. Patients without significant CAD were classified correctly 71% of the time, while those with three-VD were predicted correctly in 80%. Fully 90% of patients with predicted three-VD had two- or 3-VD. Conversely, 84% of patients predicted to have zero VD had zero or one-VD. Thus the combined use of exercise RNA and ECG data permits assessment of the presence and severity of CAD.

Aged↗
PubMed1986

The significance of underlying coronary stenosis for recovery of myocardial function after transient ischemia in the dog.

The rate of recovery of myocardial function after transient coronary occlusion (CO) has been considered to depend on the duration and frequency of CO. However, underlying coronary stenosis has not been previously demonstrated to be a determinant of the rate of myocardial functional recovery. Thus, 12 open-chest dogs were studied to examine the influence of critical coronary stenosis (CCS) on functional recovery after transient CO. Regional functional recovery following 2-minute CO was examined under two different conditions in eight dogs: patent coronary artery stenosis and fixed CSS that exhausted coronary reserve but did not cause a deficit in resting coronary flow or regional function. Following reperfusion with the coronary artery patent, regional function in the ischemic zone was fully recovered (100 +/- 18.0% of pre-CO value) at 30 seconds and was significantly increased (postischemic hypercontraction) compared to pre-CO value at 1 and at 2 minutes after reperfusion. Following CO and reperfusion in the setting of CCS, regional functional recovery was delayed and regional function remained depressed until 2 minutes after reperfusion. No cumulative effect on functional recovery following repeated 2-minute CO was demonstrated in a control group of four dogs. We conclude that coronary artery patency is a determinant of the rate of myocardial function recovery after a transient ischemic episode, and postischemic hypercontractility was suppressed by the underlying CCS.

Animals↗
PubMed1986

Effects of previous myocardial infarction on measurements of reactive hyperemia and the coronary vascular reserve.

The measurement of coronary vascular reserve by the reactive hyperemic response to ischemia has been advocated as a practical method of assessing the physiologic significance of coronary stenoses. Because the concept of measuring coronary blood flow during maximal vasodilation assumes a normal arteriolar network and viable myocardium, the presence of previous myocardial infarction may cause a significant decrease in the coronary reserve unrelated to the severity of a coronary stenosis itself. To determine the potential importance of this effect, rest and hyperemic coronary blood flow were measured in 14 dogs in the regions subtended by the left anterior descending and left circumflex coronary arteries. One hour occlusion of the left anterior descending artery followed by reperfusion was performed in 10 dogs; the 4 remaining dogs in which no occlusion was performed served as control animals (group 3). One week later, rest and hyperemic blood flow measurements were repeated in all 14 dogs. Of the 10 dogs undergoing left anterior descending artery occlusion, 5 had a large infarct (group 1) and 5 had a small infarct (group 2). In group 1 in the 1 week study, both the coronary reserve in the left anterior descending artery zone and the ratio of the coronary reserve in this zone and the left circumflex artery zone decreased compared with values before occlusion (from 425 +/- 134 to 150 +/- 34% and from 1.56 +/- 0.40 to 0.68 +/- 0.31, respectively; both p = 0.007).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Analysis of phases of contraction during graded acute myocardial ischemia.

The quantitative effects of graded ischemia on the phases of contraction in ischemic and nonischemic myocardium were studied in 10 open-chest dogs. During progressive coronary stenosis, an index of the overall severity of ischemia, total myocardial blood flow deficit (TMFD), was measured using microspheres. Segment shortening (% delta L) during the isovolumic and ejection phases of systole in the ischemic and nonischemic zones was obtained with ultrasonic crystals. In the ischemic zone, total systolic and ejection phase % delta L decreased progressively as stenosis increased; isovolumic phase % delta L showed segment elongation (bulging) during mild ischemia, which was unchanged as ischemia became severe. Total % delta L in the nonischemic zone increased progressively with increasing stenosis, reaching 132 +/- 20% of the control value when TMFD was 24.8 +/- 6.5% of total expected left ventricular (LV) myocardial blood flow. The increase in total % delta L was entirely attributable to increased ejection % delta L and correlated with indices of preload (multivariate r = 0.65) and afterload (multivariate r = 0.62). Multiple linear regression analysis revealed that augmented contraction in the nonischemic zone was best described (multivariate r = 0.94) by a combination of four hemodynamic variables estimating LV preload and afterload, which correlated in turn with the overall severity of ischemia. Thus systolic bulging in the ischemic zone is primarily an isovolumic phase phenomenon that develops initially with mild ischemia. Little additional change occurs in the isovolumic phase as ischemic severity increases, although further reductions in shortening occur in the ejection phase.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗
PubMed1986

Analysis of systolic bulging. Mechanical characteristics of acutely ischemic myocardium in the conscious dog.

To determine the mechanical factors affecting regional segmental motion after acute coronary occlusion, we studied seven conscious dogs, instrumented with sonomicrometers. Loading conditions were changed by the withdrawal of 500 ml of blood and the transfusion of 800 ml of blood. To express segmental motion, percent systolic shortening, percent systolic elongation, and early diastolic shortening were calculated. Blood withdrawal decreased left ventricular preload, increased percent systolic elongation (from 6.9 +/- 3.1% to 9.9 +/- 3.5%) and early diastolic shortening (12.9 +/- 5.3% to 16.6 +/- 5.3%), and decreased percent systolic shortening. Blood transfusion increased left ventricular preload, decreased percent systolic elongation (to 5.2 +/- 1.8%) and early diastolic shortening (8.8 +/- 2.9%), and increased percent systolic shortening. Manipulation of loading did not change regional myocardial blood flow. In acutely ischemic myocardium, the tension-length loop showed an exponential upstroke during isovolumic systole and a nearly superimposed exponential downstroke during the isovolumic relaxation phase after systole, compatible with essentially passive movement as seen with an elastic material. The changes in loading conditions affected the tension-length curve to a very minor extent. The uniformity of the curve and its exponential shape explain the load-dependency of systolic bulging and segmental motion. It is concluded that systolic bulging depends on the change in the preload tension due to the compliant portion of tension-length curve, and that shortening of ischemic myocardium during the isovolumic relaxation phase is a completely passive phenomenon.

Animals↗
PubMed1985

Sinus rhythm mapping in healed experimental myocardial infarction: contrasting activation patterns for inducing ventricular tachycardia versus fibrillation.

The inducibility of ventricular tachycardia (VT) and fibrillation (VF) is variable in healed myocardial infarction (MI) in the dog. To better understand the electrophysiologic basis for these arrhythmias, MI was produced in dogs by ligating the left anterior descending artery. One week later, epicardial mapping was performed with the dog in sinus rhythm using a hand-held bipolar electrode. Transmural mapping was performed with the dog in sinus rhythm with 4 pairs of bipolar electrodes mounted on a #14 needle. Ventricular arrhythmias were induced by the S1S2S3 technique or 3- to 5-beat burst pacing at twice diastolic threshold. Only VF could be induced in 11 dogs, while sustained VT was induced in 6 dogs. Significantly more marked and more extensive delay in activation was seen both in the epicardium and transmurally in dogs with VT than in dogs with VF. In addition, dogs with VT had morphologic evidence of a large transmural MI, whereas dogs with VF had only a subendocardial MI. It is concluded that inducible sustained VT in the dog is usually associated with a large transmural MI and an activation sequence in sinus rhythm characterized by an extensive area of marked delay in activation. This activation pattern in sinus rhythm presumably is necessary to provide the underlying electrophysiologic milieu for sustained reentry.

Animals↗
PubMed1985

Importance of total life consumption of cigarettes as a risk factor for coronary artery disease.

Cigarette smoking is an established risk factor for the occurrence of cardiovascular events and mortality. Whether recent smoking history or total life consumption best represents the increased risk due to smoking has not been previously established. Thus, stepwise logistic regression analysis was used to determine the relative contributions of these factors to the risk of having significant coronary artery disease in 1,349 patients who underwent cardiac catheterization. Six risk factors were analyzed: total pack-years, current packs smoked per day, age, gender, family history and symptomatic status. The results of this analysis showed that total pack-years, but not current packs per day, is a significant independent risk factor for the development of coronary artery disease. This was true in every age group up to but not older than age 70 years. Although the overall risk was lower in younger patients and in patients with less typical symptoms of angina, the relative risk in cigarette smokers relative to pack-years was consistently greater. The risk of total life consumption of cigarettes is thus greater than has heretofore been realized, particularly in persons who would otherwise be categorized as low risk.

Adult↗
PubMed1985

A sequential approach to the diagnosis of coronary artery disease using multivariate analysis.

There has been considerable interest in recent years in enhancing the accuracy of noninvasive tests in diagnosing coronary artery disease. The recognition that no currently available test is a perfect predictor has led to the use of probability analysis as a means of assessing the presence or absence of coronary disease. In this article we present a multivariate approach to the diagnosis of coronary disease. One hundred forty-seven patients undergoing coronary angiography, thallium-201 imaging, and exercise ECG were studied. Patients were classified according to age, sex, and typical vs atypical chest pain. Sequential stepwise logistic regression analysis was performed to develop probability statements prior to testing, after exercise ECG, and after exercise ECG and thallium-201. The results indicate that this sequential approach can be used to develop strategies for the diagnosis of coronary disease in the same way as Bayes' theorem, while permitting integration of multiple characteristics into one model.

Adult↗
PubMed1985

Relation between left ventricular global and regional function and extent of myocardial ischemia in the canine heart.

To develop a quantitative relation between the overall severity of acute ischemia and left ventricular global and regional function, two minor axis internal diameters and myocardial wall thickness were determined using ultrasonic crystals in 10 open chest dogs with carotid-left anterior descending artery cannulation. The overall extent of ischemia produced by graded stenosis of the cannulation system was estimated by total myocardial blood flow deficit, calculated using radioactive microspheres and a balloon-reservoir perfusion technique permitting precise separation of ischemic from nonischemic tissue. Although cardiac output and left ventricular stroke work were maintained through chamber enlargement until total myocardial blood flow deficit was about 10%, ejection indexes of left ventricular function decreased progressively with increasing ischemia and correlated inversely with total myocardial blood flow deficit (r = -0.55 to -0.73). Ejection indexes of left ventricular global function correlated directly with regional function in the ischemic zone (r = 0.67 to 0.83), although global function decreased at a far slower rate than regional contraction during progressive coronary stenosis with an ischemic region comprising about 25% of total left ventricular weight. During myocardial ischemia, regional dysfunction resulted in progressive global contractile dysfunction; left ventricular hemodynamic status was maintained until ischemia was severe.

Animals↗