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Biomedical subjects

R H Falk

Publications and source records attributed to R H Falk.

At least 55 records · Page 3Linked to original sources
PubMed1996

Should all patients with atrial fibrillation receive warfarin? Evidence from randomized clinical trials.

Anticoagulants should be used more widely in patients with atrial fibrillation. Legitimate concerns exist about the risk/benefit ratio in younger patients with no risk factors and in patients over the age of 75 years. Use of lower doses of anticoagulation (potential target range INR of 1.5-2.5) than used heretofore is probably the solution to most of the problems associated with anticoagulation, but conclusive proof of the efficacy of this strategy is needed. Although aspirin may reduce the risk of stroke the effect may be no more than among patients with a similar level of cardiovascular risk factors and in sinus rhythm. As such, aspirin is a valid alternative for patients with atrial fibrillation at a low risk of stroke but should not be used as an excuse to withhold anticoagulants in patients at greater risk. Several larger studies investigating the effects of different intensities of anticoagulation and the use of aspirin-warfarin combinations are underway. Indeed SPAF-III, comparing a combination of low dose warfarin and aspirin with formal anticoagulation has been stopped and reported in March 1996. A summary of the results will appear in the July issue. Identification of the minimum effective dose of warfarin and effective monitoring systems remain a priority.

Aspirin↗
PubMed1995

Aggravation of postcardioversion atrial dysfunction by sotalol.

OBJECTIVES: This study determined the effect of sotalol on atrial function after electrical cardioversion of atrial fibrillation. BACKGROUND: After electrical cardioversion of atrial fibrillation, the Doppler mitral A wave is often diminished, representing impaired atrial contractile function. Sotalol is an effective atrial antiarrhythmic drug with class III and beta-adrenergic blocking properties. Although the negative inotropic effect of sotalol on the ventricle is minimal in patients with normal ventricular function, it may manifest negative inotropy when ventricular function is impaired. We postulated that after cardioversion, when intrinsic atrial function is impaired, sotalol may have an adverse effect on the atrium. METHODS: Thirty-seven patients enrolled in a randomized, double-blind study of sotalol for maintenance of sinus rhythm were studied by quantitative Doppler echocardiography within 24 h of electrical cardioversion and, for those still in sinus rhythm, again at 1 month. Doppler variables (E and A wave velocities and integrals) in patients receiving sotalol were compared with those in patients receiving placebo. RESULTS: After electrical cardioversion, peak A wave velocity and A wave time-velocity integral in the 20 patients receiving placebo were reduced compared with normal values. In the 17 patients receiving sotalol (median dose 320 mg twice daily) these variables were further reduced (mean [+/- SD] peak A wave velocity 19.4 +/- 5.5 vs. 38.4 +/- 14.7 cm/s, p < 0.001 and mean A wave time-velocity integral 1.7 +/- 0.6 vs. 3.4 +/- 1.4 cm, p < 0.001, in sotalol- vs. placebo-treated patients, respectively). Early diastolic filling (E wave variables) did not differ between sotalol- and placebo-treated groups. At 1 month, five sotalol- and six placebo-treated patients remained in sinus rhythm, and A wave variables had increased for the whole group, with a greater increase in sotalol-treated patients. CONCLUSIONS: After electrical cardioversion, when atrial stunning is prominent, sotalol has a negative atrial inotropic effect. This effect may be temporary, as suggested by resolution at 1 month. Negative inotropic effects of antiarrhythmic drugs on the atrium should be considered in assessing Doppler variables of left ventricular filling.

Adult↗
PubMed1995

Atrial thrombi occurring during sinus rhythm in cardiac amyloidosis: evidence for atrial electromechanical dissociation.

Thrombus formation in the left atrium is rare in patients in sinus rhythm. In three patients with extensive cardiac amyloidosis transthoracic echocardiography showed large atrial thrombi in or protruding into the body of the left atrium during sinus rhythm. Doppler studies showed no A wave on mitral inflow. Severe atrial and ventricular infiltration by amyloid may have resulted in mechanical atrial standstill with resultant thrombus formation. These findings suggest that patients with severe cardiac amyloidosis may require anticoagulation when atrial function is impaired.

Adult↗
PubMed1994

Current management of atrial fibrillation.

A resurgence of interest in atrial fibrillation has led to research in several avenues. Observations on the behavior of the atrium during atrial fibrillation demonstrate that electrical activity is not entirely random and that sinus node activity persists despite surrounding fibrillation. Anticoagulation therapy for chronic atrial fibrillation is now accepted as optimal treatment, but randomized trials have excluded the majority of patients screened and the risk-benefit ratio of therapy in the average patient therefore remains unclear. This is being addressed in comparative trials of warfarin and aspirin and in an analysis of risk factors for stroke derived from a major trial. Assessment of the efficacy of therapy for the control of ventricular rate in atrial fibrillation has underscored the slow action of digoxin and raised the issue of suboptimal dosing. With the recognition that improvement of exercise capacity following cardioversion may be postponed for weeks, several studies have evaluated serial changes in ventricular function and shown that in some patients sinus rhythm is associated with an improved ejection fraction. Transesophageal echocardiography is an area of intense interest for the identification of patients at high risk of thromboembolism following cardioversion, and the significance of left atrial spontaneous echo contrast as well as the left atrial appendage contractile function are being investigated. Finally, new methods of arrhythmia termination are being evaluated and developed, and surgical approaches to atrial fibrillation are being expanded and refined.

Animals↗
PubMed1994

Flecainide.

Flecainide is a Class IC antiarrhythmic agent whose primary electrophysiologic effect is a slowing of conduction in a wide range of cardiac tissues. It is well absorbed and effective in suppressing isolated premature ventricular contractions (PVCs) or nonsustained ventricular arrhythmia but has only a modest efficacy when electrophysiologic testing is used as an endpoint. Its adverse effect on mortality in the CAST trial suggested a propensity to proarrhythmia--a phenomenon to which the Class IC agents appear particularly prone. Despite the applicability of the CAST study only to patients with a prior myocardial infarction, there has been a shift away from flecainide in ventricular arrhythmia, but the low noncardiac side effect profile of the agent allows for its continued use in a wide variety of supraventricular arrhythmias.

Atrial Fibrillation↗
PubMed1993

External cardiac pacing using low impedance electrodes suitable for defibrillation: a comparative blinded study.

OBJECTIVES: The objective of this study was to determine whether the threshold for successful cardiac pacing is affected by electrode impedance and whether this procedure can be successfully carried out through low impedance electrodes that are also suitable for defibrillation. BACKGROUND: Reintroduced in the early 1980s, external cardiac pacing utilizes large externally placed electrodes with a high impedance, in conjunction with a stimulator capable of producing an impulse of 20 to 40 ms in duration. On the basis of empiric observation, high impedance electrodes (> 500 omega) are believed to be optimal for external cardiac pacing. Such electrodes are unsuitable for defibrillation, a technique that is most successful when impedance is low. In view of the absence of controlled data to support this recommendation, as well as the desirability of using one set of electrodes for both pacing and defibrillation, we undertook the following study. METHODS: Thirty-two normal subjects underwent a total of 110 attempts at external cardiac pacing with either (or both) high or low impedance electrodes in combination with one or two commercially available external cardiac pacemakers. Each subject underwent pacing at least twice in a randomized double-blind fashion to determine the pacing threshold and level of discomfort. RESULTS: Individual subjects had a wide range of pacing thresholds but did not experience any greater discomfort with one pacemaker-electrode combination than with any other. Similarly, no pacemaker-electrode combination was superior to another in terms of pacing thresholds. The mean pacing threshold was 72.5 +/- 6 mA for the 40-ms impulse/high impedance electrode combination, 78.7 +/- 6 mA for the 40-ms impulse/low impedance electrode, 73.8 +/- 7 mA for the 20-ms impulse/high impedance electrode and 77.5 +/- 7 mA for the 20-ms impulse/low impedance electrode (p = NS for all comparisons). CONCLUSIONS: Contrary to previous belief, a high impedance electrode offers no advantage for external pacing in terms of either pacing threshold or discomfort level during pacing. This study demonstrates that it is feasible to perform external pacing through an electrode that is also suitable for defibrillation and suggests that a single external pacing-defibrillation electrode is all that is needed to perform these two procedures.

Adult↗
PubMed1993

Pacemaker therapy in patients with atrial fibrillation.

Pacing is indicated in patients with AF when clinical symptoms are readily attributable to slow ventricular rate and prolonged ventricular pauses. When choosing a pacemaker for implantation, one should consider the importance of a reasonable chronotropic response to exercise and provide a rate-responsive system (VVIR) for those patients who show chronotropic incompetence. In the case of paroxysmal AF, an AV synchronized system may provide protection against deterioration to chronic AF and heart failure and is preferred over VVI pacing, providing that paroxysms are infrequent. Drug-pacemaker interaction is rare, but it is recommended that class IC antiarrhythmic agents should not be used in pacemaker-dependent patients. Cardioversion should be performed with care in patients with a permanent pacemaker, and certain protective measures must be employed to avoid pacemaker destruction or malfunction. Pacemakers, when used according to strict criteria, constitute an integral part of treatment and may improve the quality of life and facilitate the use of necessary drugs in selected patients with AF.

Adrenergic beta-Antagonists↗
PubMed1993

Left ventricular systolic dysfunction precipitated by verapamil in cardiac amyloidosis.

Cardiac amyloidosis produces a restrictive cardiomyopathy with impaired diastolic function. We report a case in which low-dose verapamil resulted in marked worsening of congestive heart failure, as a result of a profound negative inotropic effect. Withdrawal of verapamil therapy demonstrated a return of systolic function to normal with improvement in heart failure. We postulate that patients with cardiac amyloidosis may be exceptionally sensitive to the negative inotropic effects of calcium-channel blockers either because of abnormal binding to amyloid fibrils or because their usual vasodilator effects are blunted.

Amyloidosis↗