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Influence of drugs on the relationship between sinus node recovery time and calculated sinoatrial conduction time in man.

Sinus node recovery time (SRT), the pacing rate with the maximal SRT, and calculated sinoatrial conduction time (SACT) were studied by overdrive atrial pacing and programmed premature atrial stimulation in 78 patients before and after the application of several antiarrhythmic drugs or of atropine. The maximum SRT was usually observed at lower rates of atrial pacing after application of a drug that prolonged SACT, whereas the opposite behaviour was observed in the majority of cases in whom the drug tested shortened calculated SACT. However, this relationship was not observed in all cases which may be due to random changes of sinus node automaticity or sinoatrial conduction, or to the inability of programmed premature atrial stimulation to detect changes of SACT. The results of this study further substantiate the importance of the properties of sinoat;ial conduction for achieving a maximal depression sinus node activity during high rate atrial pacing.

Anti-Arrhythmia Agents↗

Selection of an antiarrhythmic drug for a sudden-death-prevention trial.

Several therapeutic approaches have sought to prevent the occurrence of sudden cardiac death. Many sudden deaths are presumed to be due to an arrhythmia, but the drugs best known for antiarrhythmic activity, the local anesthetic agents, have not been suitable prophylactic agents because of their toxicities and other undesirable pharmacologic characteristics. Several new drugs in this class have been synthesized and are currently being tested for antiarrhythmic activity in clinical trials. One of them may prove to be worthy of a large-scale clinical trial to determine whether chronic arrhythmia suppression reduces the risk of sudden death. The characteristics of the "ideal" antiarrhythmic agent are discussed, and a brief summary of the drugs currently being tested in the United States is presented. The discussion of each drug emphasizes the characteristics that might make it suitable--or unsuitable--for use in a sudden-death trial. Many agents being tested are clearly not satisfactory for such a trial. However, they may be prototypes for an ideal drug or combination of drugs that might yet be developed.

Acecainide↗

Drug conversion of nonsustained ventricular tachycardia to sustained ventricular tachycardia during serial electrophysiologic studies: identification of drugs that exacerbate tachycardia and potential mechanisms.

Eleven of 83 patients who had ventricular tachycardia (VT) and underwent serial electrophysiologic study (EPS) had a more severe VT induced while receiving a particular antiarrhythmic drug as compared to control study. For all patients only nonsustained VT was initiated during control study, while sustained VT occurred during drug testing with disopyramide (2 patients), quinidine (2 patients), amiodarone (4 patients), and encainide (7 patients), although spontaneous arrhythmias appeared well-controlled prior to repeat testing. Pacing techniques used to induce sustained VT were the same as those used in the control study in eight patients and "less aggressive" in three patients. Almost all episodes of sustained VT resulted in substantial hypotension, especially in patients who were taking encainide. Drugs associated with sustained VT increased the median tachycardia cycle length by 112 msec (p less than 0.005) but increased the median ventricular effective refractory period by only 30 msec (p less than 0.02). Assuming re-entry was responsible for VT, we postulate that drugs facilitated initiation of sustained VT by prolonging activation time but only minimally increasing refractoriness of the tachycardia circuit.

Adult↗

New directions in antiarrhythmic drug therapy.

Cardiac arrhythmia causing sudden cardiac death is a serious worldwide public health problem. Antiarrhythmic agents have been available for therapy, but the conventional agents cause a high degree of intolerable side effects. The recent development of many new experimental antiarrhythmic agents has increased our capacity to effectively treat cardiac arrhythmias. Using a multifaceted approach of programmed electrical stimulation studies, drug level determinations, exercise testing and 24-hour ambulatory Holter monitoring, it can reasonably be decided which patient needs therapy and if therapy is going to be effective. Both aspects of the sudden death equation, ectopy frequency (triggering mechanism) and the ability to propagate sustained ventricular tachycardia (substrate), may be examined. Careful follow-up is needed to determine continued drug efficacy and the presence of side effects that may compromise patient compliance with therapy. If side effects intervene that may cause continued therapy to be intolerable, changing the antiarrhythmic agent, as opposed to decreasing the dosage to an ineffective range, may be appropriate. A comprehensive approach to arrhythmia management may begin to reduce the high incidence of sudden death due to fatal arrhythmias.

Adrenergic beta-Antagonists↗

Ventricular ectopy: etiology, evaluation, and therapy.

Ventricular ectopy occurs commonly. Its significance is related to the degree of complexity and the associated cardiac substrate. Coronary artery disease is the most frequent underlying cause, followed by cardiomyopathy and valvular disease. Symptomatic ventricular arrhythmias require treatment, whereas benign simple ventricular ectopy does not; however, the treatment of asymptomatic high-grade ventricular ectopy remains controversial. Therapy first must be directed toward the cardiac disease. Evaluation of the patient includes Holter monitoring, echocardiography, radionuclide studies, exercise testing, cardiac catheterization, and electrophysiologic testing. Programmed stimulation is useful in the diagnosis and prognosis of ventricular tachycardia, as well as in the evaluation of drug regimen efficacy. After treatment of ischemia and/or failure, specific antiarrhythmic agents, conventional and investigational, alone or in combination, are systematically selected. Should medical therapy alone be insufficient, consideration is given to surgical procedures such as subendocardial resection or ventriculotomy, often in combination with bypass grafting, aneurysmectomy, or valvular replacement. Electronic devices, including pacemakers or automatic internal defibrillators, may also be useful in certain selected cases. Suggested guidelines are proposed for a standardized approach, although therapy for each patient must still be individualized.

Adrenergic beta-Antagonists↗

Liquid chromatography in the monitoring of plasma levels of antiarrhythmic drugs.

High-performance liquid chromatography has been employed in the development of assay methods for six antiarrhythmic drugs, disopyramide, lidocain, tocainide, procainamide, aprinidine and quinidine. Liquid-solid chromatography has been used and separation times of about 5 min have usually been sufficient. Owing to the capacity of the liquid chromatographic system, sample preparation has been minimized to a single extraction and direct injection of a considerable part of the extract. The overall time of analysis is very short and the methods are well suited for monitoring of plasma levels of the antirrhythmic drugs and in some instances (procainamide and disopyramide) also for their main metabolites. UV detection at the optimal wavelength has permitted determinations down to 50 pmole (20 ng) in 1 ml of plasma for the amines with high absorbance.

Anilides↗