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At least 1,747 records · Page 97Linked to original sources
PubMed1975

Mechanism of action of antidysrhythmic drugs on ventricular conduction as studied with intramural electrodes.

Using the Dürrer electrode needle to record the intramural electrogram and a standard peripheral electrocardiogram (ECG) lead as reference, the authors studied the action of 9 different drugs in the conduction system of dogs. The authors concluded that diphenylhydantoin and lignocaine would be useful in dysrhythmias related to increased excitability and perhaps increased automatism. Ajmaline and quinidine may be some of some interest in dysrhythmias due to conduction disturbances; and, finally, ajmaline, diphenylhydantoin, di-isopyramide and quinidine may be useful in dysrhythmias due to focal re-entry.

Ajmaline↗
PubMed1978

Electrode-catheter arrhythmia induction in the selection and assessment of antiarrhythmic drug therapy for recurrent ventricular tachycardia.

We performed intracardiac electrophysiologic studies in 33 patients with recurrent ventricular tachycardia. Nineteen patients underwent one, 10 patients two, and four patients three serial electrophysiologic studies. Ventricular tachycardia was successfully induced in 83% of the patients, and pacing methods were successful in terminating tachycardia in 71% of the studies, although pacing-induced acceleration of ventricular tachycardia occurred at least once in 36% of the studies. Seventeen of the 33 patients (52%) required a total of 24 external direct current cardioversions during study. In 21 patients a variety of antiarrhythmic drugs were given I.V. and attempts at ventricular tachycardia induction were repeated to assess prophylactic effects of the drugs. An acutely effective drug or combination of drugs was found in 15 of the patients (71%). Fourteen of the 15 were placed on chronic oral therapy with the effective agent and were followed for an average period of 8.1 months (range one to 33 months). In all 14 patients we could document complete (13 patients) or partial (one patient) long-term prophylaxis against ventricular tachycardia. We conclude that drug efficacy trials in patients with recurrent ventricular tachycardia using intracardiac pacing techniques is a rapid and accurate method of selecting effective long-term antiarrhythmic therapy.

Administration, Oral↗
PubMed1983

The response to procainamide during electrophysiologic study for sustained ventricular tachyarrhythmias predicts the response to other medications.

We evaluated 126 patients with inducible sustained ventricular tachyarrhythmias to assess whether the response to procainamide during electrophysiologic study could predict responses to other conventional antiarrhythmic agents and combinations of agents. Thirty of 42 patients in whom tachycardia was not inducible after the administration of procainamide and 69 of 84 patients in whom ventricular tachycardia was inducible after procainamide underwent serial electrophysiologic studies. Forty-three of 67 antiarrhythmic regimens (64%) tested in the patients in whom ventricular tachycardia could not be induced after procainamide prevented induction of ventricular tachycardia, compared with 10 of 145 regimens (7%) tested in the patients in whom ventricular tachycardia could be induced after procainamide. Sixty of the 69 patients in whom ventricular tachycardia remained inducible after procainamide had ventricular tachycardia induced on all other conventional antiarrhythmic regimens tested. By comparison, of the 30 patients in whom ventricular tachycardia became noninducible after procainamide, 25 had no ventricular tachycardia inducible on at least one other antiarrhythmic regimen tested. Thus, the response to procainamide accurately predicted the response to other conventional antiarrhythmic agents during electrophysiologic study.

Adolescent↗
PubMedDate not supplied

Mechanism of benefit of negative inotropes in obstructive hypertrophic cardiomyopathy.

BACKGROUND: Drugs with negative inotropic effect are widely used to decrease obstruction in hypertrophic cardiomyopathy (HCM). However, the mechanism of therapeutic benefit has not been studied. METHODS AND RESULTS: We used M-mode, two-dimensional, and pulsed Doppler echocardiography to study 11 patients with obstructive HCM before and after medical elimination of left ventricular outflow tract obstruction. We measured 148 digitized pulsed Doppler tracings recorded in the left ventricular cavity 2.5 cm apical of the mitral valve. Successful treatment slowed average acceleration of left ventricular ejection by 34% (P=.001). Mean time to peak velocity in the left ventricle was prolonged 31% (P=.001). Mean time to an ejection velocity of 60 cm/s was prolonged 91% (P=.001). Before treatment, left ventricular ejection velocity peaked in the first half of systole; after successful treatment, it peaked in the second half (P=.001). In contrast, after treatment, we found no change in peak left ventricular ejection velocity. We also found no change in the distance between the mitral coaptation point and the septum, as measured in two planes, indicating no treatment-induced alteration of this anatomic relationship. CONCLUSIONS: Medical treatment eliminates mitral-septal contact and obstruction by decreasing left ventricular ejection acceleration. By slowing acceleration, treatment reduces the hydrodynamic force on the protruding mitral leaflet and delays mitral-septal contact. This, in turn, results in a lower final pressure gradient.

Aged↗
PubMed1987

A receptor for type I antiarrhythmic drugs associated with rat cardiac sodium channels.

We assessed the effects of type I antiarrhythmic drugs on the binding of ligands to receptors on voltage-sensitive sodium channels of rat cardiac myocytes. The radioligand was [3H]batrachotoxinin A 20 alpha-benzoate ([3H]BTXB), a toxin that binds to the sodium channel. The 8 drugs tested inhibited [3H]BTXB binding in a dose-dependent fashion with IC50 values from 1.34 microM for O-demethylencainide to 811 microM for procainamide. A log-log plot of IC50 versus mean therapeutic serum concentration yielded a regression line with slope of 1.17 and r of 0.95. Scatchard analysis of [3H]BTXB binding showed that lidocaine reduced the maximal binding without altering the KD for [3H]BTXB binding, indicating allosteric inhibition. The inhibition by lidocaine of [3H]BTXB binding was reversible within 30 minutes when the samples were diluted from 390 to 39 microM lidocaine. In other studies, the stereoisomers of tocainide were shown to have a threefold to fourfold difference in IC50 for inhibition of [3H]BTXB binding. The binding of antiarrhythmic drugs to this site is saturable, reversible, and stereospecific and occurs at pharmacologically relevant concentrations with similar rank order of potency in vivo and in vitro. This suggests that binding at this site relates to pharmacologic activity.

Animals↗
PubMed1982

Effects of antiarrhythmic agents on cardiac function.

Many, if not most antiarrhythmic drugs, even with differing pharmacologic properties, are capable of myocardial depression. That this has not occurred commonly with most drugs currently available may reflect several factors. These may include depression of myocardial function which is not clinically overt or which is masked by preexisting cardiac decompensation, limitation of dosages because of the difficulty in accurately determining a therapeutic endpoint, and the lack of physician awareness of the effects of these drugs on myocardial performance. However, as techniques for monitoring and quantifying arrhythmia permit more aggressive drug therapy, and as more drugs become available for clinical use, the incidence of clinically overt myocardial depression from anti-arrhythmic therapy will undoubtedly rise. Hopefully, awareness of the hemodynamic effects of these drugs and applications of new technology permitting accurate, noninvasive assessment of left ventricular function will identify and hence limit the occurrence of toxic hemodynamic effects, as well as permit the usage of maximum dosages of antiarrhythmic drugs when warranted by clinical circumstances.

Adrenergic beta-Antagonists↗
PubMed1983

The usefulness of Holter monitoring in the evaluation of antiarrhythmic drug efficacy for tachycardia.

Using Holter monitoring tachycardia was found in 145 out of 2058 patients suffering from various underlying diseases. Three thousand seven hundred and forty monitorings were performed. The mean age of patients was 54.5 years with a range of 19 to 83 years. The observed tachycardia was classified into three types: tachycardia with short duration, tachycardia with long duration and tachycardia with complex form. The attacks of tachycardia were more frequently observed during periods of physical activity than during sleeping periods. The relationship of the number of tachycardia with short duration between 24-hour Holter monitorings was examined in order to establish day to day variability of the attacks. The 95% confidence interval about the resultant regression line was calculated and the percent reduction required for the evaluation of drug efficacy to avoid the chances of interference of spontaneous variation was found to be about 44.0, 55.0 and 82% when the total number of attacks during a 24-hour period were 50, 100 and 1,000, respectively. Holter monitoring showed higher positive results as compared to exercise testing for detection of tachycardia. Higher correlation coefficients between numbers of premature ventricular contractions (PVCs) and the plasma concentrations of procainamide or N-acetylprocainamide were observed in 3 or more successive PVCs than in individually occurring PVCs. Using repeated 24-hour Holter monitorings a significant reduction in the number of tachycardia was observed when the therapeutic concentration was reached after the combined or single administration of the drug. These results suggest that repeated Holter monitorings, exercise testing and determination of plasma level of the drug may be useful for the evaluation of antiarrhythmic drug efficacy for tachycardia.

Adult↗
PubMed1985

The usefulness of electrophysiological-pharmacologic studies in the long-term therapy of paroxysmal tachycardias.

In 96 cases of paroxysmal tachycardia, results of chronic pharmacological assessment (CPA) were compared with acute electrophysiological-pharmacologic assessments (EPA) to evaluate the usefulness of EPA. I. Patients with sustained VT (31 cases): Sustained VT and repetitive ventricular response (RVR) could be induced in 61% and 23% respectively. More than one effective drug was found by EPA for 23 of 24 subjects. Of the 22 followed by CPA, the effectiveness of medication was excellent for 14 (64%), moderate for 1, slight for 4, and ineffective for 3 (14%). II. Patients with non-sustained VT (23 cases): RVR could be induced in 52%. Effective medication was identified by EPA for 8 of 10 patients. Of the 7 followed by CPA, the effectiveness of medication was excellent for 2(28.5%) moderate for 2, and ineffective for 3. III. Patients with PSVT (42 cases): PSVT could be induced in 90% of cases. Effective medication was found for all 31 cases which underwent EPA. Of the 23 cases followed by CPA, the chronic efficacy of drugs was excellent for 7 (30%), moderate for 5 (22%), slight for 7 (30%), and noneffective for 4 (18%). Therefore, we conclude that the usefulness of EPA differs according to the type of tachycardia. EPA is most useful in predicting chronic results for patients with sustained VT, especially when the sustained VT is readily reproducible by electrical stimulation. It is less useful for nonsustained VT and PSVT. With nonsustained VT, EPA is limited by difficulty in repeatedly inducing RVR, and by difficulty in predicting the appropriate medication for chronic oral therapy. With PSVT, even though the PSVT can be induced with greater success, EPA is limited by variations in pharmacologic effects over time, which create discrepancies between EPA and CPA.

Administration, Oral↗
PubMed1989

The effects of class IA antiarrhythmic drug on the common type of atrial flutter in combination with pacing therapy.

In 11 patients with common type of atrial flutter (common AF), rapid atrial pacing from the high right atrium was performed before and/or after class Ia antiarrhythmic drug administration, confirming transient entrainment by decreasing the pacing cycle length by 10 ms. In 10 patients before the drug administration, common AF was not interrupted although the pacing cycle length was decreased to 200 ms in 5 patients, accelerated atrial flutter or atrial fibrillation was induced in 4 patients, and common AF was converted into sinus rhythm in only 1 patient. After the drug administration common AF was converted into sinus rhythm in 5 out of 6 patients. The class Ia antiarrhythmic drug prolonged the common AF cycle length (255 +/- 12 ms vs. 298 +/- 37 ms, p less than 0.005) and widened the entrainment zone (64 +/- 7 ms vs. 90 +/- 20 ms, p less than 0.05). The widening of the entrainment zone and the prolongation of the common AF cycle length facilitate the successful conversion of common AF at a longer pacing cycle length, which would not precipitate atrial fibrillation or accelerated atrial flutter. The combination therapy of rapid atrial pacing and the class Ia antiarrhythmic drug is thought to be useful in the therapy of common AF.

Adult↗