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Biomedical subjects

L N Horowitz

Publications and source records attributed to L N Horowitz.

At least 73 records · Page 4Linked to original sources
PubMed1985

Usefulness of electrophysiologic testing in evaluation of amiodarone therapy for sustained ventricular tachyarrhythmias associated with coronary heart disease.

The prognostic importance of electrophysiologic studies in patients with sustained ventricular tachyarrhythmias treated with amiodarone was prospectively studied in 100 consecutive patients. Sustained ventricular tachycardia (VT)/ventricular fibrillation (VF) was inducible in all patients before amiodarone therapy. After amiodarone administration 2 groups of patients were identified. In group 1 patients the ventricular tachyarrhythmia was no longer inducible and in group 2 patients the arrhythmia remained inducible. In group 1, no recurrent arrhythmia occurred during a follow-up of 18 +/- 10 months. In group 2, 38 of 80 patients (48%) had arrhythmia recurrence during a follow-up of 12 +/- 9 months. The difference between group 1 and 2 could not be explained by clinical variables, amiodarone doses or plasma concentrations, or electrocardiographic variables. In patients in whom cardiovascular collapse or other severe symptoms where noted during electrophysiologic study after amiodarone treatment, recurrences caused sudden death (n = 12). However, in patients in whom the induced arrhythmia produced moderate symptoms, the recurrent arrhythmia was nonfatal VT (n = 26). Electrophysiologic testing provides clinical guidance and predicts prognosis in patients treated with amiodarone as it does for the evaluation of other antiarrhythmic agents.

Adult↗
PubMed1985

The clinical electrophysiology of intravenous indecainide.

The electrophysiologic effects of indecainide, a new class IC antiarrhythmic agent, were assessed in 10 patients with left ventricular dysfunction and inducible sustained ventricular tachycardia. Indecainide was administered intravenously in a dose of 60 to 90 mg/kg at a rate of 12.5 to 15 micrograms/kg/min. Indecainide had no effect on sinus node function or atrial and ventricular effective refractory periods. The AH (106 +/- 13 vs 130 +/- 24 msec, p less than 0.002) and HV (57 +/- 7 vs 73 +/- 19 msec, p less than 0.001) intervals were significantly increased. The QRS duration increased (102 +/- 9 vs 120 +/- 13 msec, p less than 0.001); however, the JT duration did not change. Induction of ventricular tachycardia was prevented in 1 of 10 patients. In the remaining nine patients, the ventricular tachycardia cycle length was significantly prolonged (248 +/- 47 vs 320 +/- 71 msec, p less than 0.001). Indecainide significantly depressed intracardiac conduction at several sites.

Adult↗
PubMed1985

A review of the uses and limitations of tocainide--a class IB antiarrhythmic agent.

In conclusion, it appears that tocainide will be an extremely important new antiarrhythmic agent in the armamentarium of the clinical cardiologist (Table V). Its similarity to lidocaine and the predictability of its efficacy in patients responsive to lidocaine is an important note. Its lack of interaction with beta blockers and digoxin is also a promising feature. While tocainide has proven to be effective in the prophylaxis and treatment of patients with both refractory and chronic ventricular arrhythmias, its efficacy is in the approximate range of other class I agents, such as quinidine, procainamide, and disopyramide. Its side effect profile appears to be similar in percentage to the adverse effects of quinidine, but often these side effects are milder, better tolerated, and respond to dosage alteration. Thus, tocainide will undoubtedly prove to be a useful new antiarrhythmic agent, particularly when compared to the currently available antiarrhythmic agents.

Animals↗
PubMed1985

Ischemia at rest is independent of the extent of ventricular dysfunction and arrhythmias in patients with coronary artery disease.

To assess the relation between myocardial ischemia, ventricular arrhythmias (VA), and left ventricular (LV) dysfunction, we evaluated 74 patients with coronary artery disease (CAD) using radionuclide angiography (to determine the resting ejection fraction [EF]), resting thallium-201 scintigraphy (to ascertain the extent of resting ischemia), and 24-hour Holter monitoring (to assess VA). Thirty patients had resting ischemia, 26 had resting EF less than 30%, and 27 had repetitive VA. Patients with and without ischemia had similar EFs (36 +/- 14 vs 38 +/- 14, p = NS). Further, patients with and without repetitive forms of VA had a similar number of resting ischemic segments (1.1 +/- 1.7 vs 1.1 +/- 2.2, p = NS). Patients with EFs less than 30 had more VA than patients with EFs greater than or equal to 30 (Holter class 4.3 +/- 2.3 vs 3.0 +/- 1.8, p less than 0.01) but a similar extent of ischemia (1.4 +/- 2.2 vs 1.0 +/- 1.7, p = NS). Thus, while patients with lower EFs have more repetitive forms of VA, ischemia at rest is independent of VA and EF. These data suggest that prognostic stratification of patients with CAD for intervention studies should include a separate consideration of ischemia.

Arrhythmias, Cardiac↗
PubMed1985

Effect of long-term amiodarone therapy on thyroid hormone levels and thyroid function.

Both hyperthyroidism and hypothyroidism have been noted to occur in some patients treated with amiodarone for cardiac arrhythmias. To determine the frequency of the development of thyroidal abnormalities in patients receiving amiodarone, 45 euthyroid patients were prospectively evaluated. Serum samples were obtained for measurement of thyroxine, thyrotropin, triiodothyronine, and triiodothyronine resin uptake prior to initiation of amiodarone treatment and serially over a 12- to 27-month period during which amiodarone was administered. The patients were divided into four subgroups as follows: Group I (n = 22) had elevated thyroxine levels, Group IIA (n = 13) had normal thyroxine levels and normal thyrotropin levels, Group IIB (n = 7) had normal thyroxine levels and elevated thyrotropin levels, and Group III (n = 3) had subnormal thyroxine levels. Demographic factors (such as route of administration, cardiac diagnosis, sex of the patient, or indication for amiodarone therapy) and amiodarone levels had no significant effect on the thyroid hormone parameters. However, Group I patients were statistically older than the patients in the other groups. Linear regression analysis revealed a negative correlation for thyroxine levels and a positive correlation with thyrotropin levels with age for the whole group. The various groups were not statistically affected by duration of therapy, but a positive trend existed for increasing thyroxine levels. Although virtually all patients showed changes in their thyroid hormone levels, chemical hyperthyroidism (elevated thyroxine and triiodothyronine levels without symptoms) developed in only two patients (4 percent), and clinical hyperthyroidism (elevated thyroxine and triiodothyronine levels with symptoms) developed in no patients. Four patients (9 percent) became biochemically and clinically hypothyroid. Thus, amiodarone frequently influences thyroid hormonal parameters, but less commonly causes a change in actual thyroid function. However, hyperthyroidism and hypothyroidism do occur in a significant number of patients.

Age Factors↗
PubMed1985

Limitations of failure of procainamide during electrophysiologic testing to predict response to other medical therapy.

To determine whether failure of procainamide to prevent initiation of ventricular tachyarrhythmias during electrophysiologic testing predicted failure of other antiarrhythmic regimens, 81 consecutive patients with coronary artery disease whose ventricular tachyarrhythmias remained inducible during procainamide administration were studied. Overall, 26 (12%) of 216 subsequent drug studies were successful and at least one effective drug regimen was identified in 22 (27%) of the 81 patients. Drug success was significantly related to the arrhythmia induced at baseline study; 7% of drug studies were successful in patients with sustained ventricular tachycardia, 24% in patients with ventricular fibrillation, and 29% in patients with nonsustained ventricular tachycardia. An effective drug regimen was found in 11 (19%) of 59 patients with sustained ventricular tachycardia, 4 (50%) of 8 patients with ventricular fibrillation and 7 (50%) of 14 patients with nonsustained ventricular tachycardia. In patients with sustained ventricular tachycardia, failure of procainamide to suppress the arrhythmia correlated with failure of other agents used singly but not in combination. This study supports the view that when procainamide fails to prevent initiation of the arrhythmia in patients with inducible sustained ventricular tachycardia it is unlikely that other individual standard agents will be effective. However, combination regimens may suppress the arrhythmia and should be evaluated. In patients with nonsustained ventricular tachycardia, all agents should be evaluated because failure to respond to procainamide does not predict subsequent responses to other agents either alone or in combination.

Adult↗
PubMed1985

Use of amiodarone in the treatment of persistent and paroxysmal atrial fibrillation resistant to quinidine therapy.

The efficacy of amiodarone was assessed in 38 patients with atrial fibrillation resistant to quinidine and an effort made to identify factors correlated with amiodarone response. The study group included 29 patients with and 9 without organic heart disease and either persistent (n = 11) or paroxysmal (n = 27) atrial fibrillation. All patients were treated with amiodarone and followed up in a research clinic. Efficacy was classified as excellent (no recurrent symptomatic atrial fibrillation) in 15 (55%) of 27 patients with paroxysmal and 5 (45%) of 11 patients with persistent atrial fibrillation. Efficacy was poor (no effect on atrial fibrillation) in 5 (19%) of 27 patients with paroxysmal and 6 (55%) of 11 patients with persistent atrial fibrillation. Efficacy was good (amelioration but not total suppression) in 7 (26%) of 27 patients with paroxysmal atrial fibrillation. Efficacy was related to echocardiographic left atrial dimension, left ventricular ejection fraction and, in patients with persistent atrial fibrillation, the duration of the arrhythmia. During the follow-up period of 15 months (range 1 to 36), overall efficacy (considering response and toxicity) was 67% in the 27 patients with paroxysmal and 45% in the 11 patients with persistent atrial fibrillation. It is concluded that amiodarone offers an additional therapeutic alternative in quinidine-resistant atrial fibrillation and that certain clinical factors are correlated with amiodarone response.

Adult↗
PubMed1985

Electrophysiologic testing in patients at high risk for sudden cardiac death. I. Nonsustained ventricular tachycardia and abnormal ventricular function.

Nonsustained ventricular tachycardia, although usually asymptomatic, is associated with a high risk of sudden cardiac death in patients with depressed left ventricular function. To test the vulnerability of such patients to symptomatic and potentially life-threatening arrhythmias, complete electrophysiologic studies were performed in 58 patients with clinically documented nonsustained ventricular tachycardia (greater than or equal to three complexes but less than 15 seconds of self-terminating ventricular tachycardia by 24 hour ambulatory electrocardiographic [Holter] or telemetric monitoring) and abnormal left ventricular function (ejection fraction less than 50% by radionuclide angiography). All patients had nonsustained ventricular tachycardia in the absence of antiarrhythmic drugs, acute ischemia, long QT syndrome, recent infarction or electrolyte abnormalities. The stimulation protocol for each patient included the introduction of single, double and triple ventricular extrastimuli at three cycle lengths (sinus, 600 and 450 ms) and two right ventricular sites (apex and outflow tract). A sustained ventricular tachyarrhythmia was induced in 23 patients (40%) and a nonsustained ventricular tachycardia in 14 patients (24%). Induction of sustained tachycardia correlated with the presence of akinesia or aneurysm, or both, by radionuclide angiography, but not with ejection fraction or presence or absence of coronary artery disease. These results indicate that: 1) patients with clinical nonsustained ventricular tachycardia and chronic left ventricular dysfunction have a high incidence of inducible sustained ventricular tachycardia or ventricular fibrillation; and 2) electrophysiologic testing may allow further substratification of risk of sudden cardiac death in high risk patients with nonsustained ventricular tachycardia.

Adult↗
PubMed1985

Improved method for evaluating ventriculoatrial conduction before implantation of atrial-sensing dual chamber pacemakers.

Pacemaker-mediated tachycardia may occur when a spontaneous ventricular premature depolarization is retrogradely conducted to the atrium with a ventriculoatrial (VA) interval that exceeds the atrial refractory period of an atrial-sensing dual chamber pacemaker. Previous methods for evaluating VA conduction have failed to predict clinical occurrences of pacemaker-mediated tachycardia. In this study, maximal VA intervals after ventricular extrastimuli during atrial or atrioventricular (AV) sequential pacing were compared with intervals measured by the standard method of ventricular pacing. VA intervals were 201 +/- 53 ms during ventricular pacing and 224 +/- 52 ms after ventricular extrastimuli during atrial pacing (p = NS). VA intervals were 305 +/- 77 ms after ventricular extrastimuli during AV sequential pacing and were longer than VA intervals during ventricular pacing (p less than 0.001) or after ventricular extrastimuli during atrial pacing (p less than 0.01). Thus, the ventricular extrastimulus technique during AV sequential pacing reveals substantially longer VA intervals than does ventricular pacing and explains why pacemaker-mediated tachycardia might occur when pacemaker atrial refractory periods are designed or programmed according to VA intervals measured only during ventricular pacing.

Adult↗
PubMed1985

Conversion from intravenous to oral mexiletine in the acute management of repetitive ventricular arrhythmia.

We evaluated the safety and efficacy of intravenous mexiletine and a method for converting from intravenous to oral mexiletine therapy. Fifteen patients with repetitive ventricular ectopy (13 had ventricular tachycardia) received intravenous mexiletine at a rate of 10 mg/min for 30 to 60 minutes. Ventricular ectopy was suppressed with minimal side effects in 10 of 15 subjects. Oral mexiletine was begun immediately after completion of the intravenous infusion at a dose of 10 mg/kg/24 hr in the 10 responders to intravenous therapy. In eight, the oral dose was effective in suppressing the arrhythmia, but it induced side effects in three of them. In one of these three, dose reduction resulted in adequate arrhythmia control with acceptable toxicity. In the two who did not respond to the original dose, a larger dose (15 mg/kg/24 hr) induced arrhythmia control with acceptable side effects in one subject. Thus rapid control of nonsustained repetitive ventricular arrhythmia can be achieved with intravenous mexiletine in about two thirds of patients, and conversion to oral therapy can often be achieved smoothly without significant arrhythmia recurrence.

Administration, Oral↗
PubMed1985

Tocainide: a new oral antiarrhythmic agent.

Tocainide, a newly released class 1B antiarrhythmic agent, has membrane stabilizing and electrophysiologic characteristics similar to those of lidocaine, but it can be prescribed for oral administration. Investigational studies in both animals and humans have shown tocainide's effectiveness for the treatment of ventricular arrhythmias in chronic and acute settings. The drug has nearly 100% bioavailability after oral administration and an effective half-life of 9 to 37 hours (mean, 15 hours). Antiarrhythmic efficacy is similar to that of other class I medications currently in use. Serious side effects most frequently involve the central nervous or gastrointestinal system and occur in 10% to 20% of patients. Tocainide has minimal negative inotropic effects and a tendency to shorten effective refractory periods.

Administration, Oral↗
PubMed1985

ST segment and T wave abnormalities.

ST segment and T wave changes are the most common ECG abnormalities. Interpretation must be correlated with other clinical and laboratory information to avoid overestimating or underestimating their significance. Classic causes include left ventricular hypertrophy, digitalis glycosides, and ischemic heart disease. Notched or bifid T waves have been reported in a variety of syndromes. In the geriatric population, they are most commonly associated with psychoactive drugs or CNS disorders.

Aged↗
PubMed1985

Invasive cardiac electrophysiologic testing.

The indications for clinical electrophysiologic study have continued to evolve since the introduction of this technique in the mid 1960s. They now include evaluation of sinus node dysfunction, AV conduction disturbances, syncope of unknown etiology, supraventricular arrhythmias with and without Wolff-Parkinson-White syndrome, sustained ventricular tachycardia, and out-of-hospital cardiac arrest. The rate of complications for this procedure is acceptable, with the potential benefits being accurate diagnosis and prescription of therapy.

Anticoagulants↗
PubMed1984

Flecainide: its proarrhythmic effect and expected changes on the surface electrocardiogram.

The proarrhythmic potential and electrophysiologic effect of flecainide acetate, a potent class IC anti-arrhythmic agent, are considered in this report. Although the definition of a proarrhythmic effect is arbitrary, several such definitions are discussed and applied to data on flecainide. In patients with chronic ventricular arrhythmias, an increase in VPC frequency developed in 0 to 4% of patients, compared with 1 to 8% of patients who received quinidine and 2% who received encainide, another class IC agent. In patients with acute hemodynamically significant ventricular arrhythmias, the proarrhythmic effects were noted in 5 to 12%. Proarrhythmic effects appear to be more common in patients with left ventricular dysfunction and life-threatening ventricular arrhythmias. The depression of atrioventricular conduction produced by flecainide is similar to that seen with other class IC agents. Increases in PR and QRS intervals are related to dose and plasma concentration and are approximately 25% at therapeutic levels. These changes in the electrocardiographic intervals do not appear to carry important clinical implications and do not require discontinuation of flecainide. QT prolongation is absent or minimal with flecainide. Guidelines for management of patients with flecainide are suggested.

Anti-Arrhythmia Agents↗
PubMed1984

Correlation between changes in R wave amplitude and left ventricular volume induced by rapid atrial pacing.

To examine the Brody effect in humans, we studied 15 patients by means of coronary sinus pacing. We measured left ventricular (LV) volumes from the cardiac output (measured by the thermodilution technique) and LV ejection fraction (measured by radionuclide ventriculography). Pulmonary blood volume was determined by means of cardiac output and mean pulmonary transit time. In six patients, pacing was performed at two different rates, resulting in 21 pacing measurements. The heart rate increased with pacing from 73 +/- 11 to 119 +/- 19 bpm (mean +/- standard deviation, p less than 0.001). The end-diastolic volume (EDV) and the end-systolic volume (ESV) decreased with pacing (p less than 0.001 each). The R wave amplitude decreased with pacing (1.44 +/- 0.63 mV control vs 1.32 +/- 0.58 mV with pacing; p less than 0.01). R wave amplitude decreased in 19 of the 21 pacing studies (90%); EDV and ESV decreased in all 21 pacing studies, and pulmonary blood volume decreased in 14 of the 15 pacing studies (93%) performed in 11 patients. There was a significant correlation between the percentage of change in R wave amplitude with the percentage of change in EDV (r = 0.54, p less than 0.01) and with the percentage of change in ESV (r = 0.54, p less than 0.01). These results, therefore, validate Brody's hypothesis and indicate that changes in LV volumes affect the R wave amplitude.

Adult↗