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Biomedical subjects

V Bhargava

Publications and source records attributed to V Bhargava.

At least 145 records · Page 8Linked to original sources
PubMed1981

Myocardial infarction diminishes both low and high frequency QRS potentials: power spectrum analysis of lead II.

Previous studies based primarily on counts of QRS notches and slurs have suggested that myocardial infarction (MI) increases high frequency QRS components. However, this technique does not quantitatively measure total high frequency voltage. To further study this problem, a microprocessor ECG system was employed capable of averaging multiple QRS complexes to reduce noise. Power spectrum analysis of the QRS using a Fast Fourier Transform was then performed in lead II in ten normal subjects and ten patients with prior inferior MI. The infarct group showed a decrease in QRS potentials over a broad frequency range (7.81-304.7 Hz). Therefore, contrary to previous estimates, MI may attenuate high as well as low frequency QRS potentials as part of a general decrease in electromotive force.

Adult↗
PubMed1981

The relationship between exercise-induced R wave amplitude changes and QRS vector loops.

The mechanism for R wave amplitude changes during exercise testing is controversial. To investigate this, we recorded vectorcardiograms (VCG) during supine rest and bicycle exercise in 13 normals and 33 patients with coronary heart disease. In all normals, and in those CHD patients with an exercise-induced decrease in R wave amplitude, there was a posterior shift of the QRS vector loop in the transverse plane. In the CHD patients with an increase or no change in R wave amplitude, there was an anterior shift of the QRS vector loop. Though spatial vector length decreased with exercise and correlated with R wave changes, there was a better correlation between changes in the maximal QRS vector angle and R wave amplitude. The etiology of R wave changes during exercise appears to be mainly due to shifts in QRS vector loops, but the reason for these shifts is unknown.

Adult↗
PubMed1981

Temporal stability of the high frequency QRS waveform in normal subjects.

Previous attempts to assess high frequency QRS components relied primarily on counts of QRS notches and slurs. In order to measure high frequency potentials in a more quantitative manner, we adapted a commercially-available microprocessor ECG system equipped with a signal-averaging program to reduce noise and an 80-300 Hz digital band-pass filter. The high frequency QRS output was digitized for measurement of its root-mean-square (RMS) value. Serial high frequency recordings were then obtained in ten normal subjects approximately 100 days apart. Both the morphology and RMS voltage of the high frequency signal were stable over this time period. Furthermore, comparison of inter- and intra- observer variability in making these computer assisted RMS measurements revealed a high degree of reproducibility. This new technique offers a reliable way of quantitatively measuring high frequency QRS potentials and should be useful in assessing serial changes in various pathologic states.

Action Potentials↗
PubMed1981

Effect of myocardial infarction on high-frequency QRS potentials.

Studies have shown that the number of high-frequency QRS notches increases after myocardial infarction (MI). To assess overall high-frequency (greater than 80 Hz) potentials more quantitatively, we adapted filtered and the root-mean-square (RMS) voltage of the residual (80-300 Hz) signal computed. High-frequency RMS values were significantly (p less than 0.01) greater in leads II, III and aVf in normal subjects (n = 12) than in patients with inferior infarction (n = 12). Similarly, high-frequency RMS values were higher (p less than 0.01) in leads V2 and V5 in normal subjects (n = 14) than in patients with prior anterior MI (n = 14). A reduction in high-frequency RMS values with inferior infarction was independently confirmed using Fourier analysis of the QRS in lead II. QRS notching in these subjects was also quantified by computing the number of baseline crossings of the first derivative (dV/dt). As predicted, notching was significantly greater (p less than 0.05) both with inferior MI (lead II) and anterior MI (lead V5). However, contrary to classic theory, the number of notches correlated negatively with direct measurements of high-frequency RMS voltage in lead II (r = -0.63) and lead V5 (r = -0.49). Positive correlations were obtained between high-frequency potentials and two new indexes that measure the amplitude of QRS dV/dt-peak-to-peak amplitude of dV/dt and RMS dV/dt. Using these indexes, absolute separation of inferior MI patients and normal subjects was obtained. We conclude that MI increases low-amplitude QRS notching but diminishes total high-frequency voltage, probably because of an overall decrease in electromotive potentials and slowing of ventricular conduction.

Adult↗
PubMed1981

Peak rate of left-ventricular ejection by a gated radionuclide technique: correlation with contrast angiography.

Gated radionuclide cardiac blood-pool imaging can produce reliable estimates of left-ventricular (LV) volume and ejection fraction. The ventricular volume curve can be used to develop normalized ejection rates, since count volumes and framing times are known. To test the accuracy of the peak ejection rate (maximum dv/dt), as derived by a standard computer algorithm, we studied 15 patients with coronary artery disease by both contrast ventriculography and radionuclide angiography. Max dv/dt by the radionuclide technique correlated well with the angiographic result: r = 0.92, p less than 0.01. The mean intraobserver variation was (plus or minus 12%) and the mean interobserver variation plus or minus 0.33 end-diastolic volumes per sec (plus or minus 13%). We conclude that maximum dv/dt may be derived from gated blood images, with reasonable accuracy and modest variability.

Adult↗
PubMed1980

Quantitation of left ventricular wall motion in normal subjects: comparison of various methods.

Computer-assisted analysis of percent change in the square root of area in each of 12 consecutive 30-degree, pie-shaped ventricular segments was obtained in 48 normal subjects who underwent cardiac catheterization and left ventriculography. The information obtained permitted establishment of objective confidence limits for normal left ventricular regional wall motion. As an index of dynamic changes in segmental wall motion, the percent change in the square root of area method compared favorably with existing radius, area, hemichord, and chord methods. It also possessed a variety of theoretical advantages over these techniques: 1) large numbers of points were analyzed, 2) wall motion disorders in all areas except base were evaluated, 3) taking the square root of area's percent change provided both area information with least splay and an average measure of radius.

Adult↗
PubMed1980

Semiautomated method for evaluation of left ventricular regional wall motion in coronary artery disease.

Regional left ventricular wall motion was independently assessed in 436 patients using both subjective visual inspection of ventriculograms and objective computer-determined percent change in the square root of the area between systolic and diastolic outlines. Agreement between subjective and objective techniques was greatest at the ventricular apex and least at the base and partly dependent on the number of abnormal segments present. Objective analysis of regional wall motion provides a permanent quantitative record of wall motion and shows good agreement with meticulous subjective inspection of ventriculograms. As such, it has potential as an adjunct to ventriculography.

Coronary Disease↗
PubMed1980

Effect of myocardial infarction on the peak amplitude of high frequency QRS potentials.

Studies based on analysis of QRS notching and slurring have suggested an increase in high frequency QRS potentials following myocardial infarction (MI). We investigated the sensitivity and specificity of an indirect, but easily quantitated index of high frequency potentials--the peak-to-peak amplitude of the high frequency signal. A commercially-available micro-processor ECG system was employed with a QRS-averaging program to reduce random noise and an 80-300 Hz filter to selectively record higher frequency potentials. High frequency ECGs were recorded in leads II, III and aVF in 40 normal men and 41 patients with prior inferior MI. Peak-to-peak amplitude of the high frequency signal was less than or equal to 35 micro V in one or more of these leads in 18 of 41 MI patients (44%) compared with only 1 of 40 normals (2.5%) (P < 0.001). In the infarct group, reduced peak amplitude of the high frequency signal was also noted in some leads where the standard ECG did not show pathologic Q waves. This diminution in peak amplitude probably reflects a reduction in high frequency voltage. Therefore, contrary to previous theory, MI may actually cause a decrease in high frequency potentials as part of an overall loss of electromotive force or a slowing of conduction associated with myocardial necrosis. Quantitative high frequency QRS measurements may be of critical value in selected cases.

Adult↗
PubMed1979

Instantaneous transmitral blood flow and anterior mitral leaflet motion in man.

Transmitral blood flow was measured in man by numerical differentiation of left ventricular volume as a function of time in 11 patients undergoing cardiac catheterization. Using this technique, transmitral blood flow may be studied in a variety of pathologic states without the need for surgically introduced flowmeters. Just before left ventriculography, echocardiography of the mitral valve was performed. The pattern of transmitral blood flow was strikingly similar to the diastolic movement of the anterior mitral leaflet. At any equivalent diastolic filling time, the percent of the integrated area beneath the curve inscribed by the diastolic anterior mirtal leaflet echoes closely approximated the percent of stroke volume which had entered the left ventricle. This observation supports the hypothesis that mitral leaflet motion accurately reflects transmitral flow. Consequently, at a given time during diastole, the relative velocity of transmitral flow and the percent of the stroke volume which has entered the left ventricle may be approximated noninvasively from the anterior mitral leaflet echogram.

Adult↗
PubMed1978

Electrophysiologic and hemodynamic effects of verapamin. Correlation with plasma drug concentrations.

Verapamil was administered intravenously to 30 open-chest dogs and the electrophysiologic and hemodynamic effects of the drug were correlated with the corresponding plasma concentrations. At concentrations below 152 ng/ml, verapamil prolonged the A-H interval, abolished ventriculoatrial conduction, but did not significantly change sinus rate, cardiac output, left ventricular dp/dt, of systemic vascular resistance. Concentrations above 200 ng/ml were associated with slowing of the sinus rat, high degree atrioventricular block during atrial pacing, 24% decrease in mean aortic pressure, and decreased cardiac output and left ventricular dp/dt. Sinus arrest, high degree atrioventicular block during sinus rhythm, decreased systemic vascular resistance and increased left ventricular end-diastolic pressure occurred when plasma verapamil concentrations exceeded 400 ng/ml. These results show that plasma verapamil concentrations reliably reflect the electrophysiologic and hemodynamic actions of the drug, and that "therapeutic" drug effects can be achieved at plasma concentrations at which myocardial depressant effects are unlikely.

Animals↗
PubMed1978

Alteration of the left ventricular diastolic pressure-segment length relation produced by the pericardium. Effects of cardiac distension and afterload reduction in conscious dogs.

Left ventricular pressure and segment length were measured in seven conscious chronically instrumented dogs with the pericardium intact and 3-9 days after pericardiectomy. Diastolic pressure-length plots were obtained under control conditions and after acute volume loading followed by sodium nitroprusside infusion. In all dogs with intact pericardium, volume loading displaced the entire diastolic pressure-length curve upwards and sodium nitroprusside shifted it toward control. After pericardiectomy the pressure-segment length data during control, volume loading and sodium nitroprusside fell on a single curve (intercepts and slopes not statistically different); After dextran infusion, intrapericardial pressure rose from control 1.5 +/- 0.7 mm Hg to 8.2 +/- 0.5 mm Hg, and it fell to 4.8 +/- 0.1 mm Hg after nitroprusside. Therefore, in acute cardiac dilatation the pericardium contributed significantly to the increased left ventricular diastolic pressure and to the fall during sodium nitroprusside infusion and appeared responsible for shifts in the diastolic pressure-segment length relation.

Animals↗
PubMed1976

Cardiac amyloidosis, contrictive pericarditis and restrictive cardiomyopathy.

Cardiac amyloidosis is not characterized by a single hemodynamic pattern. Some of the cases present the clinical findings of restrictive cardiomyopathy and in these differentiation from constrictive pericarditis remains difficult in spite of the introduction of techniques designed to assess myocardial contractility and ventricular diastolic compliance. The clinical features and the demonstration of left ventricular diastolic pressure greater than right remain the most useful means of distinguishing restrictive cardiomyopathy from constrictive pericarditis. In other cases of cardiac amyloidosis the diastolic pressure is elevated throughout diastole and ventricular ejectile ability is lost. These cases do not simulate constrictive pericarditis and should not be classified as restrictive cardiomyopathy.

Amyloidosis↗