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Biomedical subjects

D Mehta

Publications and source records attributed to D Mehta.

At least 37 records · Page 2Linked to original sources
PubMed1989

Significance of signal-averaged electrocardiography in relation to endomyocardial biopsy and ventricular stimulation studies in patients with ventricular tachycardia without clinically apparent heart disease.

Signal-averaged electrocardiography (ECG) was performed in 38 patients (mean age 38 years, range 15 to 70) with ventricular tachycardia who had no clinical evidence of structural heart disease. Spontaneous ventricular tachycardia was nonsustained in 23 patients and sustained in 15. None of the patients had symptoms of heart failure or ischemic heart disease, and at cardiac catheterization none had significant coronary artery disease or left ventricular wall motion abnormalities. In addition, all patients underwent left and right ventricular endomyocardial biopsy and ventricular stimulation studies. Signal-averaged ECG was performed and late QRS potentials were defined with use of Simson's method. Late QRS potentials were detected in a minority (18%) of patients including 2 of 23 with nonsustained and 5 of 15 with sustained (p = NS) ventricular tachycardia. Fifteen patients (40%) had abnormal endomyocardial biopsy results and these findings were more common in patients with sustained than in those with nonsustained ventricular tachycardia (9 of 15 versus 6 of 23, p less than 0.05). Late potentials were associated with abnormal endomyocardial biopsy findings (6 of 15 versus 1 of 23, p less than 0.01). An increase in fibrous tissue was the most frequent histopathologic abnormality; this increase was quantified by morphometric methods and compared with biopsy findings in normal control subjects. In the control group the proportion of collagen in relation to myocytes was less than 10%. All patients with both late potentials and abnormal biopsy findings had a greater than 15% ratio of collagen to myocytes in at least one specimen and the biopsies revealed marked interstitial fibrosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Respiratory responses to sustained isometric muscle contractions in man: the effect of muscle mass.

1. Respiratory responses to sustained isometric contractions of a small mass of muscle (the finger flexors) during handgripping, and of a larger mass of muscle (the quadriceps) during extension of the leg at the knee, have been studied in man. 2. For both masses of muscle the increases of ventilation and of oxygen consumption were greater for contractions at 40% maximum voluntary contraction (MVC) than for contractions at 20% MVC. 3. The increase of ventilation was not related to the mass of muscle involved. 4. At 20% MVC oxygen consumption during contraction of the quadriceps was greater than that during handgripping. At 40% MVC the oxygen consumptions were similar. The oxygen debts following both handgrip and knee extensor contractions at 20% MVC were negligible. Following 40% MVC contractions of the quadriceps a significant oxygen debt was recorded but no debt was apparent following 40% MVC contractions of the finger flexors. 5. The increases of ventilation during isometric exercise were generally inappropriately high for the increases of gas exchange. This led to reductions of the end-tidal carbon dioxide pressure (PET,CO2), especially towards the end of exercise. 6. Following 40% MVC handgripping hyperventilation continued despite the reduced alveolar PCO2. By contrast, following 40% MVC knee extension PET,CO2 transiently rose above the resting level, but did not stimulate ventilation. 7. It appears that following fatiguing isometric contractions hyperventilation continues and appears to be independent of alveolar PCO2. It is suggested that stimuli which increase ventilation during exercise may continue to act during the early phase of recovery.

Adult↗
PubMed1989

Optimal atrioventricular delay at rest and during exercise in patients with dual chamber pacemakers: a non-invasive assessment by continuous wave Doppler.

The optimal atrioventricular delay at rest and during exercise was investigated in nine patients with heart block and implanted dual chamber pacemakers. All patients studied had normal left ventricular function and a normal sinus node rate response to exercise. Cardiac output was measured by continuous wave Doppler and was calculated as the product of stroke distance measured by Doppler at the left ventricular outflow, aortic root area measured by M mode echocardiography, and heart rate. Pacemakers were programmed in the DDD mode. Cardiac output was measured with the patient at rest while supine and while erect and at the peak of submaximal exercise (the end of stage 1 of the Bruce protocol) with the pacemakers programmed to the following atrioventricular intervals: 75-80 ms, 100-110 ms, 140-150 ms, and 200 ms. During exercise the basic pacing rate was programmed to 70 beats/min. Cardiac output at rest while supine and erect was greatest with an atrioventricular delay of 140-150 ms and it was significantly higher than that with an atrioventricular delay of 75-80 ms. On average there was a 31% decrease in cardiac output when patients stood up. During treadmill exercise, however, cardiac output was greatest when the atrioventricular delay was 75-80 ms, and this was significantly higher than the cardiac output with atrioventricular delays of 150 and 200 ms. During exercise 1:1 atrioventricular relations were maintained in patients at all atrioventricular intervals. In patients with atrioventricular sequential pacemakers cardiac output at rest is greatest with an atrioventricular delay of 140-150 ms but during exercise the optimal atrioventricular delay is shorter. Rate modulation of the atrioventricular interval may improve the haemodynamic response and possibly exercise tolerance in patients with dual chamber pacemakers.

Adult↗
PubMed1988

Relative efficacy of various physical manoeuvres in the termination of junctional tachycardia.

The ability of four vagotonic physical manoeuvres to terminate paroxysmal junctional tachycardias was tested in 35 patients with inducible and sustained arrhythmia. Each manoeuvre was used up to three times in an attempt to terminate an induced tachycardia and was judged to be effective if it terminated two out of the three induced episodes. The Valsalva manoeuvre in the supine position was effective in 19 (54%), right carotid sinus massage in 6 (17%), left carotid sinus massage in 2 (5%), and the diving reflex in 6 (17%) cases. 4 of the 6 patients who responded to right carotid sinus massage and all patients who responded to the diving reflex also responded to the Valsalva manoeuvre. The Valsalva manoeuvre while standing was effective in 9 (20%) patients only. Patients in whom the manoeuvres terminated the tachycardias were significantly younger than those who did not respond (median age: 30 vs 45 years, p less than 0.01). Physical manoeuvres were much more successful in terminating atrioventricular re-entry tachycardias (19/24) than atrioventricular nodal re-entry tachycardias (3/11, p less than 0.01). Efficacy of the manoeuvres was related to their bradycardic effect in sinus rhythm.

Adolescent↗
PubMed1988

Clinical electrophysiologic effects of flecainide acetate.

Flecainide acetate depresses the rate of depolarization of action potential (Vmax), the so-called "membrane stabilizing action." In the intact heart it has a unique profile of substantial effect on conduction with modest effect on refractoriness. After intravenous administration, clinical electrophysiologic studies show that conduction through atrial myocardium, atrioventricular (AV) node, His-Purkinje system, and ventricular myocardium is depressed, the most prominent effect being on the His-Purkinje system. Refractorines of the normal atrial and AV nodal myocardium is not prolonged while that of the ventricular muscle is slightly increased. Atrial fibrillation (60% to 70%), atrial tachycardia (90% to 100%), and nodal and AV tachycardia (80% to 90%) are generally terminated, while flutter is usually slowed, but in a small proportion of patients (10% to 20%) might be terminated by the intravenous use of flecainide acetate. This drug has also been shown to be effective in terminating stable ventricular tachycardia (70%). However, it appears to be slightly less effective in suppressing inducibility of ventricular arrhythmias. Administered orally, flecainide is very effective in decreasing ventricular ectopic activity (80% to 95%) and nonsustained ventricular tachycardia. Thus, flecainide has a wide range of antiarrhythmic properties, making it a useful agent in the management of a variety of supraventricular and ventricular arrhythmias. In a small proportion of patients, however, its use can lead to apparent arrhythmogenic effects, the most dangerous being exacerbation of ventricular tachycardia.

Animals↗
PubMed1988

Limitations of rate response of an activity-sensing rate-responsive pacemaker to different forms of activity.

The responses of an activity-sensing rate-responsive system (Activitrax) to various forms of physiological activity were assessed in 15 individuals who had this pacemaker. Nine were patients with complete heart block and atrial arrhythmias; their mean age was 60 years (range, 41-85 years). Six were age-matched healthy volunteers who were exercised with an external Activitrax system attached firmly to the chest wall. The pacemaker was programmed to achieve a pacing rate of about 100 bpm at the end of the first stage of the Bruce protocol (pacemaker settings: rate = 70-150 bpm; threshold = low to medium; response = 6-9). In the activity-sensing ventricular pacing mode, all patients achieved a significant increase in treadmill time compared to constant-rate ventricular pacing (mean +/- SD, 8.0 +/- 3.3 vs 5.4 +/- 2.3 minutes; p less than 0.01), with a mean maximum pacing rate of 123 +/- 18 bpm. Jogging in place produced a prompt increase in pacing rate, with the maximum achieved at the end of the exercise. However, physiological activities such as hand-grip, the Valsalva maneuver and standing resulted in only minimal rate response. Pacing rate after ascending 4 flights of stairs was the same as that achieved after descending the same stairs (100 +/- 8 vs 105 +/- 4 bpm; p = 0.1). All 15 subjects were exercised from resting heart rate for 3 minutes on a treadmill at 1.2 mph and 2.5 mph with four gradients at each speed. Although the pacing rate increased with a faster treadmill speed (p less than 0.005), it did not respond appropriately to a change in gradient compared to the sinus rate. We conclude that although activity-sensing rate-responsive pacing gives a prompt increase in pacing rate and improves maximum exercise tolerance, further refinement is necessary because: (1) physiological activities not associated with significant movement are not detected by this pacing system; (2) detection of vibrations as an indicator of activities does not correlate well with the level of exertion.

Adult↗
PubMed1988

Comparative evaluation of chronotropic responses of QT sensing and activity sensing rate responsive pacemakers.

The rate responses of activity sensing (ATS) and QT sensing (QTS) rate responsive pacemakers to different forms and durations of exercises were compared. Nine patients with ATS and five with QTS were studied. All had complete heart block and atrial arrhythmias. At the onset, the pacemakers were programmed to achieve a pacing rate of 100-110 bpm by the end of stage 1 of the Bruce protocol, and to a pacing rate range of 70-150 bpm. With progressive exercise, using a treadmill (Bruce protocol), the maximum pacing rates in the two groups were not significantly different (mean +/- SD: 123 +/- 18 vs 129 +/- 23 bpm, ATS vs QTS). The time taken to return to the baseline pacing rate during recovery was significantly longer with QTS (178 +/- 70 vs 264 +/- 68 s, p less than 0.05). Brief exercise tests on a treadmill were performed for 3 min each with different combinations of treadmill speeds (1.2 and 2.5 mph) and gradients (0, 5, 10 and 15%). In both groups of patients, faster walking speed was associated with a faster pacing rate at each gradient. However, with increasing gradients, at each speed, there was a rise in the maximum pacing rate only in patients with QTS. During brief exercise tests, the maximum rate was achieved by the end of exercise in patients with ATS, but was delayed by 33 +/- 20 s after exercise in patients with QTS.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Elimination of diffraction error in acoustic attenuation estimation via axial beam translation.

Optimized wideband attenuation estimations were performed on a tissue mimicking phantom in a water tank with and without axial beam translation (ABT), and the results were compared to those from standard substitution measurements. A -17 percent discrepancy between the results of the substitution method and the optimized estimation without ABT was noted in the far field. This discrepancy was eliminated when ABT was utilized.

Models, Structural↗
PubMed1988

Recurrent paroxysmal complete heart block induced by vomiting.

A woman had a 40-year history of vomiting associated with syncope. Spontaneous and induced vomiting was predictably associated with sinus bradycardia, paroxysmal atrioventricular block, and ventricular asystole. The clinical and laboratory studies carried out to illustrate the mechanism of this unusual complication of vomiting demonstrated it to be due to a vagovagal reflex initiated by distension of upper esophagus.

Bradycardia↗
PubMed1988

Mucoepidermoid carcinoma of the lung with intracranial metastases.

Discussed is the first roentgenographic and post-mortem description of a patient with mucoepidermoid carcinoma of the lung who presented with intracranial metastases. The patient's primary tumor eluded physical diagnosis and bronchoscopic delineation. The autopsy confirmed minimal tumor involvement of the bronchial wall despite bulky regional and distant metastases.

Aged↗
PubMed1987

Flecainide acetate in the treatment of tachycardias associated with Mahaim fibres.

Patients with Mahaim fibres are susceptible to tachycardias which can be refractory to conventional drug therapy, leading to treatment with surgery and catheter ablation. The effects of flecainide acetate were studied in 3 patients (61, 21 and 35 years of age) with Mahaim fibres presenting with tachycardias refractory to beta-blockers, quinidine and verapamil. One also had ophthalmic side-effects from amiodarone. Three types of tachycardias were induced: a reentrant tachycardia with left bundle branch block morphology (LBBBM) in all 3 patients, atrial flutter in one and atrial fibrillation in another. Intravenous flecainide acetate (2 mg kg-1) terminated reentrant tachycardia and abolished duality of atrioventricular conduction in patient 1. In patient 2, it abolished preexcitation during atrial flutter prior to termination. Atrial fibrillation could not be induced in patient 3 after flecainide acetate. In all patients, retrograde conduction was blocked, preexcitation was not present with atrial pacing and no tachycardia was induced after flecainide. All have remained asymptomatic on oral flecainide acetate (100 mg bd) for a mean follow-up period of 9 months. We conclude that (1) flecainide acetate is effective for the treatment of various tachycardias associated with Mahaim fibres; (2) since different mechanisms responsible for the tachycardia with LBBBM may be present in the same patient and difficult to determine in some, treatment with flecainide acetate which affects both the atrioventricular node and Mahaim fibre conduction may be appropriate for the condition and; (3) its use should be considered before more aggressive therapies.

Adult↗
PubMed1986

QT prolongation after ampicillin anaphylaxis.

Tall T waves and pronounced prolongation of the QT interval developed 24 hours after an apparently complete recovery from an acute anaphylactic reaction to oral ampicillin in a previously healthy woman of 29. These electrocardiographic abnormalities gradually subsided over five days. The prolongation of the QT interval has not previously been reported after anaphylaxis.

Adult↗
PubMed1986

Capillary remodeling in bleomycin-induced pulmonary fibrosis.

Lung fibrosis is a process in which collagen is laid down and the delicate capillary-alveolar relationship is disturbed. The architectural changes which occur in the capillaries, a main element of the oxygen transferring unit, are difficult to illustrate without a three-dimensional tool, such as scanning electron microscopy. Therefore, a scanning electron microscopic study was undertaken to show the capillary changes of lung fibrosis. Fibrosis was induced in rats by intratracheal instillation of bleomycin. After 30 days the rats were sacrificed, and the vascular tree of the lung was cast with methacrylate. The fibrosis was patchy. The intercapillary space became wider; and some capillaries had large, irregular dilatations. Occasionally giant capillaries (up to 19 mu in diameter) were noted. The pleural and alveolar capillary diameters increased (P less than 0.01), and the branching frequency decreased (P = 0.02). The center of the capillary rings, which has been suggested to be the site of contractile interstitial cells, increased in size (P = 0.03). The appearance of irregularly shaped capillaries and an increase in diameter without a change in density of alveolar capillaries, resulting in a loss of surface area and a decrease in branching, are the main scanning electron microscopic findings of the remodeling which occurs in pulmonary capillaries in lung fibrosis. These changes may partially explain the functional derangement of this disease.

Animals↗