Robert G. Zoble

Efficacy and Safety of Oral Dofetilide in Converting to and Maintaining Sinus Rhythm in Patients With Chronic Atrial Fibrillation or Atrial Flutter The Symptomatic Atrial Fibrillation Investigative Research on Dofetilide (SAFIRE-D) Study

BackgroundThis double-blind, multicenter, placebo-controlled study determined the efficacy and safety of dofetilide in converting atrial fibrillation (AF) or atrial flutter (AFl) to sinus rhythm (SR) and maintaining SR for 1 year. Methods and ResultsPatients with AF or AFl (n=325) were randomized to 125, 250, or 500 &mgr;g dofetilide or placebo twice daily. Dosages were adjusted for QTc response and, after 105 patients were enrolled, for calculated creatinine clearance (ClCr). Pharmacological cardioversion rates for 125, 250, and 500 &mgr;g dofetilide were 6.1%, 9.8%, and 29.9%, respectively, versus 1.2% for placebo (250 and 500 &mgr;g versus placebo;P =0.015 and P <0.001, respectively). Seventy percent of pharmacological cardioversions with dofetilide were achieved in 24 hours and 91% in 36 hours. For the 250 patients who successfully cardioverted pharmacologically or electrically, the probability of remaining in SR at 1 year was 0.40, 0.37, 0.58 for 125, 250, and 500 &mgr;g dofetilide, respectively, and 0.25 for placebo (500 &mgr;g versus placebo, P =0.001). Two cases of torsade de pointes occurred, 1 on day 2 and the other on day 3 (0.8% of all patients given active drug); 1 sudden cardiac death, classified as proarrhythmic, occurred on day 8 (0.4% of all patients given active drug). ConclusionsDofetilide, a new class III antiarrhythmic agent, is moderately effective in cardioverting AF or AFl to SR and significantly effective in maintaining SR for 1 year. In-hospital initiation and dosage adjustment based on QTc and ClCr are necessary to minimize a small but nonnegligible proarrhythmic risk.

St-qR pattern: new sign for diagnosis of anterior myocardial infarction during right ventricular pacing.

In 4 patients with recent anterior wall myocardial infarction involving the ventricular septum, bipolar right ventricular apical stimulation resulted in small negative deflections preceding larger R waves (St-qR pattern) in leads I, aVL, and (except for Case 3) V6. Abnormal ST segment elevation after St-qR pattern was noted in only 2 cases. The presence or absence of repolarization changes probably reflected the stage of infarction during which electrocardiograms were obtained. The mechanisms of these changes are similar to those responsible for the qR morphology in left bundlebranch block complicated by septal infarction, as shown by the case in which both patterns were seen during spontaneous left bundle-branch block as well as during right ventricular stimulation. The St-qR pattern may not be recorded when the ventricular complexes are distorted by large spikes (as when unipolar pacing is used) or when stimulation is performed from the upper portion of the right septal surface, an area to which the infarction does not extend.

Relationship of Surface Electrogram Recordings to Activity in the Underlying Specialized Conducting Tissue

Surface electrodes are widely used to study the electrophysiology of the A-V conducting system. The recording of activity from the human in-situ His bundle represents a practical, clinically useful adaptation of surface recording technics. The interpretation of data accumulated by this means must be considered in relation to the extent to which the surface recordings from the specialized conducting system accurately reflect activity in the underlying tissue. A combination of microelectrode technics to record transmembrane action potentials and surface recording technics on isolated preparations of canine conducting tissue were used to approach this question. Under many conditions the surface electrogram was found to be an accurate indicator of the presence and timing of impulses in the conducting system. However, during early premature activity, marked decreases or complete absence of surface electrogram voltage could occur at coupling intervals at which premature impulses were still able to propagate through tissue under the electrodes. In addition, early premature activity could be associated with reversal of polarity of the surface electrogram without reversal of the direction of propagation. Inaccurate relationships between the time of inscription of the surface recording and the time of passage of the propagating wavefront beneath the surface electrodes also occurred with early premature impulses. Finally, there is some evidence that surface electrograms primarily reflect that activity in the most superficial levels of tissue.

Wide QRS Tachycardia in a Young Patient

Robert J. Hariman, MD; Maung M. Khin, MD; Robert G. Zoble, MD, PhD; Department of Cardiology, James A. Haley VA Hospital, Tampa, Florida. Dr Hariman is now with the Department of Medicine, University of Illinois College of Medicine at Peoria. A 22-YEAR-OLD HISPANIC MAN PRESENTED to the emergency department with palpitation after playing basketball. He had similar episodes of palpitation associated with exercise, which disappeared spontaneously. He denied any previous cardiac history. On examination, he appeared diaphoretic with a blood pressure of 96/60 mm Hg. His heart rate was above 200 beats/min. His lungs were clear to percussion and auscultation. The rest of his examination findings were normal. His complete blood cell count and serum electrolyte, creatinine, glucose, and troponin-I levels were normal. The presenting electrocardiogram (ECG) is shown in Figure 1. Questions: What is the treatment for this patient? What is the etiology for his rapid heart rate?