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Biomedical subjects

S F Horowitz

Publications and source records attributed to S F Horowitz.

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

Effect of variable left ventricular vertical orientation on planar myocardial perfusion images.

Differences in vertical orientation of the left ventricle within the chest cavity cannot be corrected by gamma camera positioning. The effect of variations in vertical angulation on the appearance of the diagnostically important left anterior oblique (LAO) view has not been previously evaluated. In the current study, a computer simulation of a normal left ventricle was created and "imaged," varying only the degree of vertical rotation. The effect of six vertical positions on the LAO image was assessed visually and with horizontal and circumferential profile analysis. Results indicate a homogenous distribution of counts in the horizontal views. With increasing verticality, there are fewer counts in the valve plane, while the inferoapex initially increases in count density, and then progressively decreases. Quantification revealed count variations of up to 37% in the valve plane and 45% in the inferoapex due entirely to differences in vertical orientation of the left ventricular simulation. A survey of 167 patients who underwent routine stress thallium imaging showed a vertical angulation that varied from 7 degrees to 64 degrees (mean = 37 degrees) as determined from the anterior view. Clinical images were similar in appearance to computer generated images after correction for anterior view foreshortening. The present study suggests that the accuracy of current quantitative thallium methods to detect coronary artery disease might be enhanced by the use of a revised set of normal standards corrected for vertical orientation of the left ventricle.

Computers↗
PubMed1985

Response of the right ventricle to exercise in isolated mitral stenosis.

Eight patients in sinus rhythm, with varying degrees of isolated mitral stenosis (mitral valve area 0.6 to 1.3 cm2 and total pulmonary vascular resistance 5.0 to 17.5 U-m2), underwent supine rest and symptom-limited exercise radionuclide ventriculography to determine right ventricular (RV) and left ventricular ejection fraction (EF). Cardiac catheterization with hemodynamic measurements at rest and at peak exercise was performed within 24 hours of radionuclide ventriculography. Four of the 8 patients underwent corrective mitral surgery resulting in normal mean pulmonary artery pressures and total pulmonary vascular resistance at rest. These 4 patients had repeat radionuclide ventriculography at rest and during exercise 1 to 2 months after surgery. Preoperatively, all 8 patients had an abnormal exercise RVEF response (mean change +/- standard deviation [SD], -5.0 +/- 4.5%), coincident with an increase in mean pulmonary artery pressure during exercise (mean change, 15 +/- 5.0 mm Hg). The change in RVEF from rest to exercise, corrected for duration of exercise, correlated with peak exercise mean pulmonary artery pressure (r = -0.71, p = 0.05), as well as total pulmonary vascular resistance at rest (r = -0.82, p = 0.02). Postoperatively, all 4 patients who underwent surgical correction showed a normal RVEF response during exercise (mean change +/- SD, +6.8 +/- 4.0%). Thus, in patients with acquired mitral stenosis and no coronary artery disease (1) loading conditions and not contractility are prime determinants of RV exercise response, and (2) an exercise-induced decrease in RVEF may be a sensitive marker for increased total pulmonary vascular resistance and pulmonary hypertension.

Adult↗
PubMed1985

Mechanism underlying the absence of ischemic changes on the exercise electrocardiogram in patients with abnormal exercise thallium-201 imaging and coronary artery disease.

Patients with coronary artery disease may have reversible abnormalities on a thallium myocardial perfusion study without simultaneous ischemic changes on the exercise electrocardiogram, but the mechanisms responsible for this disparity have not been fully elucidated. A group of 37 patients with angiographically demonstrated coronary artery disease and abnormal thallium perfusion imaging were divided into two groups on the basis of their exercise electrocardiographic ST segment response. Thirteen patients (Group A) had no significant electrocardiographic changes with exercise, while 24 patients (Group B) had ST changes consistent with ischemia during the test. There were no significant differences in clinical or angiographic characteristics between the two groups. Stress test results showed a similar mean duration of exercise in the two groups (6.2 +/- 1.8 versus 6.7 +/- 2.5 min, p = NS), but the patients in Group A achieved a significantly lower mean maximal heart rate (117 +/- 26 versus 132 +/- 21 beats/min, p less than 0.05) and mean maximal double product (19,650 +/- 5116 versus 22,650 +/- 4871, p less than 0.05). There was no consistent pattern of thallium perfusion abnormality noted in Group A to suggest that a particular region of electrically silent myocardium was responsible for ischemia in the absence of electrocardiographic changes. These results suggest that exercise thallium-electrocardiogram discordance is mediated by the level of myocardial workload achieved. An abnormal perfusion scan accompanying an exercise electrocardiogram which does not demonstrate any ischemic ST change may occur when there is sufficient increase in myocardial oxygen demand to result in differential augmentation of myocardial blood flow, but insufficient imbalance of supply and demand to result in signs of ischemia on the surface electrocardiogram.

Cardiac Catheterization↗
PubMed1985

Inversion of the radionuclide regurgitant index in right-sided valvular regurgitation.

Estimation of left-sided valvular insufficiency has been obtained using the ratio of left- to right-ventricular stroke counts, i.e., the regurgitant index. The present study was designed to evaluate the usefulness of the regurgitant index in identifying patients with isolated right-sided valvular insufficiency. We identified 12 patients with tricuspid or pulmonic regurgitation by at least two of the following criteria: pulsatile liver, positive Carvallo's sign, and pulsatile jugular-venous distension. In 9 of the 12 patients, the right-sided insufficiency was confirmed by catheterization or contrast echocardiography and flow-directed pulsed-echo Doppler. The regurgitant index in patients with right-sided insufficiency was 0.59 +/- 0.23. This was significantly different from patients with left-sided insufficiency (3.09 +/- 0.8; P less than 0.001) and from control subjects (1.49 +/- 0.32; P less than 0.001). In 11 of the 12 patients with right-sided regurgitant lesions, the regurgitant index was less than 1.0. The hepatic expansion fraction, a possible correlate of an expansile liver, has previously been found to be both sensitive and specific for the detection of patients with right-sided regurgitation. We calculated the hepatic expansion fraction in 6 patients with tricuspid regurgitation (including 3 with pulsatile livers) and 5 controls using the method of Handler et al.. In the present study, the hepatic expansion fraction in tricuspid-insufficiency patients was 4.3% as compared to 4.1% in normals (P = NS). In summary, this study suggests that the regurgitant index may be a sensitive tool for the diagnosis of right-sided regurgitant lesions, while the hepatic expansion fraction does not appear to be useful for identifying tricuspid insufficiency.

Adult↗
PubMed1985

Characterization and automatic identification of ECG conduction abnormalities using segmental multiharmonic Fourier analysis of gated blood-pool scintigrams.

This study of biventricular segmental timing sequences compared patterns of the first-harmonic phase with those of multiharmonic Fourier-analysis-derived parameters to determine their suitability for the classification of patients using an automatic pattern recognition scheme. The study involved nine patients with normal ECGs, six with left bundle branch block, 4 with right bundle branch block, and 6 with right-ventricular pacemakers; all patients had normal left-ventricular function. The segmental sequence described by the time of end systole was similar to that described by the first-harmonic phase, with a lower correlation using the time of maximum filling rate, and a rather poor correlation of the time of maximum ejection rate with the other parameters. Thus, despite theoretical difficulties, timing patterns described by phase best agreed with those of the time of end systole. Intersegmental timing differences were used as criteria for discriminating between groups by means of a sequential logic tree. Using either phase, time of end systole or time of maximum ejection rate, all patients were correctly classified into the four ECG categories. More intersegmental timing differences were useful as criteria for phase (57) than for the time of end systole (45) or the time of maximum ejection rate (30). The first-harmonic phase was more efficient than the time of end systole for separating patient groups. Sequential biventricular timing disorders can be objectively classified using either first-harmonic or multiharmonic Fourier analysis, and their patterns can be automatically recognized and used for classification.

Bundle-Branch Block↗
PubMed1985

Femoral pseudoaneurysm following nonpenetrating trauma in a patient with aortic insufficiency.

Although not uncommon after penetrating vascular trauma, arterial pseudoaneurysms rarely develop following blunt trauma. A patient is described in whom indirect trauma led to pseudoaneurysm of the profunda femoris artery, and persistent bleeding required surgical intervention. In this case, the coexistence of significant aortic valvular regurgitation suggests that wide pulse pressure may predispose to this arterial complication.

Aged↗
PubMed1984

Bayesian comparison of cost-effectiveness of different clinical approaches to diagnose coronary artery disease.

The objective of this study was to compare the cost-effectiveness of four clinical policies (policies I to IV) in the diagnosis of the presence or absence of coronary artery disease. A model based on Bayes' theorem and published clinical data was constructed to make these comparisons. Effectiveness was defined as either the number of patients with coronary disease diagnosed or as the number of quality-adjusted life years extended by therapy after the diagnosis of coronary disease. The following conclusions arise strictly from analysis of the model and may not necessarily be applicable to all situations. As prevalence of coronary disease in the population increased, it caused a linear increase in cost per patient tested, but a hyperbolic decrease in cost per effect, that is, increased cost-effectiveness. Thus, cost-effectiveness of all policies (I to IV) was poor in populations with a prevalence of disease below 10%, for example, asymptomatic people with no risk factors. Analysis of the model also indicates that at prevalences less than 80%, exercise thallium scintigraphy alone as a first test (policy II) is a more cost-effective initial test than is exercise electrocardiography alone as a first test (policy I) or exercise electrocardiography first combined with thallium imaging as a second test (policy IV). Exercise electrocardiography before thallium imaging (policy IV) is more cost-effective than exercise electrocardiography alone (policy I) at prevalences less than 80%. 4) Noninvasive exercise testing before angiography (policies I, II and IV) is more cost-effective than using coronary angiography as the first and only test (policy III) at prevalences less than 80%. 5) Above a threshold value of prevalence of 80% (for example patients with typical angina), proceeding to angiography as the first test (policy III) was more cost-effective than initial noninvasive exercise tests (policies I, II and IV). One advantage of this quantitative model is that it estimates a threshold value of prevalence (80%) at which the rank order of policies changes. The model also allows substitution of different values for any variable as a way of accounting for the uncertainty inherent in the data. In conclusion, it is essential to consider the prevalence of disease when selecting the most cost-effective clinical approach to making a diagnosis.

Angiography↗
PubMed1984

Relation between exercise-induced changes in ejection fraction and systolic loading conditions at rest in aortic regurgitation.

To examine the role of systolic wall stress at rest in determining left ventricular performance during exercise in aortic regurgitation (AR), systolic wall stress (measured by M-mode echocardiography) was related to changes in left ventricular function during maximal exercise (evaluated by radionuclide ventriculography) in 30 patients with chronic aortic regurgitation. Of these 30 patients, 7 had a normal exercise response, defined as an absolute increase in ejection fraction of 5% or greater (Group I) and 23 had abnormal exercise response, defined as no change (less than 5% change) or a decline (less than or equal to 5%) in ejection fraction (Group II). Patients in Group I had a significantly lower radius/wall thickness ratio (2.5 +/- 0.2 versus 3.1 +/- 0.1, p less than 0.01) and lower peak systolic wall stress (123 +/- 11 versus 211 +/- 12 X 10(3) dynes/cm2, p less than 0.01) than patients in Group II. An increase in ejection fraction during exercise was seen in 6 of the 9 patients with normal systolic wall stress at rest (less than 150 X 10(3) dynes/cm2), but in only 1 of 21 patients with elevated systolic wall stress (p less than 0.001). Peak systolic wall stress at rest varied linearly, and inversely with changes in left ventricular ejection fraction during exercise (r = 0.60, p less than 0.001). Groups I and II did not differ in ejection fraction at rest, clinical symptoms or maximal work load achieved.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1984

Accuracy and precision of regional multiharmonic Fourier analysis of gated blood-pool images.

In order to estimate the precision and accuracy of parameters derived from segmental multiharmonic Fourier analysis of gated blood-pool images, a Monte Carlo computer noise simulation was tested on five sample regional time-activity curves. The first three Fourier harmonics were retained and the precision and accuracy of parameters of ventricular function were calculated, varying the ejection fraction, segment size, and framing rate. Precision improved with higher ejection fraction, higher counts per frame, or higher framing rate. There was no change in precision as the framing rate changed at fixed total counts. Accuracy changed little with changing framing rate. Thus, for segmental analysis there is no advantage to using a higher framing rate. Regions five or more pixels in size are recommended for reliable results. This study provides useful information for the optimization of acquisition and processing conditions for regional gated blood-pool analysis.

Cardiac Output↗
PubMed1983

Can noninvasive exercise test criteria identify patients with left main or 3-vessel coronary disease after a first myocardial infarction?

This study attempts to determine whether exercise treadmill testing with clinical, electrocardiographic, and thallium-201 myocardial perfusion imaging data can identify which patients have left main or 3-vessel (anatomically high-risk) coronary artery disease (CAD) after their first transmural myocardial infarct (MI). Twelve exercise test criteria for high-risk disease were compared in 40 patients referred for cardiac catheterization; 34 had a history of chest pain and 17 had angiographically defined high-risk CAD. A thallium image defect outside the vascular distribution of the MI was the most reliable criterion to distinguish patients with high-risk CAD (p = 0.00052 for Fisher's exact test of discrimination). Thallium imaging was somewhat more sensitive (92 versus 65%, p = 0.108) when patients with negative thallium imaging criteria who failed to achieve 85% of the age-predicted maximal heart rate were excluded. Failure to achieve 85% of predicted heart rate was by itself a useful criterion for detecting high-risk CAD (p = 0.017), especially in patients not taking propranolol (p = 0.004). Development of positive S-T segment depression at less than 70% predicted heart rate also discriminated left main or 3-vessel disease from less extensive CAD (p = 0.016). Other criteria failed to discriminate significantly between high-risk and less extensive CAD in patients after their first MI (p greater than 0.05). S-T segment depression (p = 0.199) or chest pain (p = 0.577) during exercise testing were particularly unreliable. Further, none of the criteria for high-risk CAD were influenced by irreversible left ventricular dysfunction. It is concluded that patients with thallium imaging defects outside the region of the infarct, decreasing blood pressure during exercise, failure to achieve 85% of predicted heart rate, or S-T depression at less than 70% of predicted heart rate have a high probability of having left main or 3-vessel disease. Patients without these criteria have a very low probability of having high-risk CAD and probably do not need coronary angiography for the purpose of excluding these high-risk coronary lesions after a first MI.

Adult↗
PubMed1983

Quantification of cardiac conduction abnormalities using segmental vector Fourier analysis of radionuclide gated blood pool scans.

Timing abnormalities of myocardial contractility may occur as inter- or intraventricular asynchrony. Gated blood pool scintigraphy was performed on 21 patients with a normal ejection fraction and the following electrocardiograms: six normal, six with left bundle branch block, four with right bundle branch block and five with right ventricular pacemaker rhythm. A phase and amplitude of the first harmonic of the Fourier transform was obtained for each pixel, and left and right ventricles were trisected. A mean vector phase for each region was obtained by vector summation. Regional and global values were analyzed within each group and compared with normal values. The phase differences between the entire left and right ventricles (mean +/- standard deviation) were: 9 +/- 3 in the normal patients, 38 +/- 8 (p less than 0.01) in patients with left bundle branch block, -6 +/- 7 (p less than 0.05) in patients with right bundle branch block and 15 +/- 9 (difference not significant) in patients with pacemaker rhythm. The phase differences between left ventricular posterolateral and septal regions were -4 +/- 2 in the normal patients, 10 +/- 5 (p less than 0.01) in patients with left bundle branch block, -7 +/- 10 (p less than 0.05) in patients with right bundle branch block and 10 +/- 5 (p less than 0.01) in patients with pacemaker rhythm. Within the right ventricle, phase differences between the apical and septal segments were 14 +/- 9 in the normal patients, 14 +/- 10 (NS) in patients with left bundle branch block, -2 +/- 3 (p less than 0.01) in patients with right bundle branch block and -22 +/- 18 (p less than 0.01) in patients with pacemaker rhythm. Interventricular phase differences were greatest in patients with left bundle branch block and absent or reversed in right bundle branch block.(ABSTRACT TRUNCATED AT 250 WORDS)

Arrhythmias, Cardiac↗
PubMed1982

Physiological influences on perfusion imaging in transient myocardial ischaemia: importance of early distribution of thallium-201.

We tested the hypothesis that visualisation of defects on thallium-201 (201Tl) myocardial perfusion images (MPI) depends on the duration of the ischaemic state between 201Tl injection and the time of reperfusion of an occluded coronary artery. Praecordial imaging with a gamma camera was performed in 24 anaesthetised, open-chest dogs with transient coronary occlusion. Results indicated that if the duration of the ischaemic state after 201Tl injection was less than 3 min before reperfusion, then the MPI 5 to 15 min after 201Tl injection was falsely negative (201Tl activity in zone (IZ)/normal zone (NZ)greater than 0.85). Dogs which were ischaemic more than 5 min always had MPI defects 5 to 15 min after 201Tl injection (IZ/NZ201Tl ratio less than 0.85). MPI results (201Tl IZ/NZ) 15 min after 201Tl injection were determined by the duration of the ischaemic state after 201Tl injection (r = -0.86) because prolonged ischaemia allowed 201Tl to distribute from blood to myocardium before reperfusion: 201Tl (IZ/NZ( = 0.356 +/- 1.00 (fraction of total 201Tl remaining in blood at the end of the ischaemic state), r = 0.94.

Animals↗
PubMed1982

Coronary collateral function during exercise.

A totally occluded coronary vessel subtending a noninfarcted, entirely collateral-dependent myocardial region (NIECDMR) provides an opportunity to assess collateral perfusion during exercise stress. Collateral function was determined by analysis of exercise thallium-201 myocardial perfusion images from 31 patients who had at least one NIECDMR (total 41 NIECDMRs) documented during catheterization. Twenty-two of 41 NIECDMRs manifested exercise-induced perfusion defects and 19 were normally perfused. The exercise-negative NIECDMRs were further categorized: Group 1 NIECDMRs (n = 13) were associated with defects in other myocardial regions supplied by diseased vessels and were considered negative relative to other jeopardized regions; group 2 NIECDMRs (n = 6) were not associated with exercise-induced defects in other myocardial regions, which suggests that collateral perfusion was adequate during maximal exercise. Regions supplied by a diseased left anterior descending coronary artery manifested exercise defects regardless of collaterals, possibly because these regions were larger and required more perfusion. Angiographic indexes of collateral function did not clearly predict exercise results.

Adult↗
PubMed1982

Recovery of right ventricular function following repair of acute ventricular septal defect.

Ventricular septal defect is a serious complication of acute myocardial infarction with a high mortality rate. Right ventricular dysfunction, which frequently accompanies septal defect, can be due to several etiologies. We describe two cases of septal defect following infarction, with sequential studies of right and left ventricular function. Right ventricular infarction was found in both patients. Postoperatively, the right ventricular ejection fraction improved significantly. The pathophysiology and expectation for recovery are discussed.

Aged↗
PubMed1981

Quantification of valve regurgitation by radionuclide angiography before and after valve replacement surgery.

Radionuclide gated cardiac blood pool imaging was used to quantify the severity of valve regurgitation in 20 patients, by calculating the ratio of left ventricular to right ventricular stroke counts (end-diastolic minus end-systolic counts in right and left ventricular regions of interest). This ratio (the stroke index ratio) was substantially higher in patients with aortic and mitral regurgitation (3.91 +/- 1.45) than in a control group of 10 patients without regurgitation (1.32 +/- 0.15), p less than 0.001. The stroke index ratio correlated closely (r = 0.947) with measurements of regurgitant fraction derived from simultaneous determinations of total and forward stroke volumes during cardiac catheterization. After aortic and mitral valve replacement in 18 patients, the stroke index ratio decreased from 4.03 +/- 1.46 to 1.38 +/- 0.23 (p less than 0.001), a value not significantly different from that observed in patients without regurgitation. All three patients with residual postoperative regurgitation had a stroke index ratio greater than 2 standard deviations above the mean values for the control group (greater than 1.62), whereas the remaining 15 patients, who had no evidence of regurgitation, had values within the normal range. Therefore, radionuclide gated blood pool scanning provides a noninvasive method of quantifying valve regurgitation and assessing the results of medical or surgical interventions.

Adult↗