Perspectives and future trends in cellular electrophysiology: Implications for the clinician

As a result of single fiber electrophysiologic studies, the clinical approach to the electrical behavior of the heart has improved. Three areas are examined: 1) the electrocardiographic waveform, 2) normal and abnormal cardiac rhythms, and 3) the mechanism of action of antiarrhythmic drugs. In each area, the results of single fiber studies have provided a conceptual framework for diagnostic and therapeutic decisions. These studies have also enabled investigators to test hypotheses formulated from clinical observations. It may be only a slight exaggeration to attribute many of our recent advances in each of the three areas to the development and use of the microelectrode

Repolarization heterogeneity and rate dependency in a canine rapid pacing model of heart failure

Repolarization heterogeneity and rate dependency have long been established as factors contributing to arrhythmogenic risk. However there are conflicting observations regarding the nature and extent of ventricular repolarization heterogeneity that complicate understanding of arrhythmogenic mechanisms. In order to explore these disparate findings, we studied ventricular repolarization heterogeneity and rate dependency in a canine, rapid pacing model of heart failure

ACC/AHA/HRS 2008 guidelines for device-based therapy of cardiac rhythm abnormalities: A report of the American College of Cardiology/American Heart Association Task Force on practice guidelines (Writing Committee to revise the ACC/AHA/NASPE 2002 guideline update for implantation of cardiac pacemakers and antiarrhythmia devices)

This revision of the “ACC/AHA/NASPE Guidelines for Implantation of Cardiac Pacemakers and Antiarrhythmia Devices” updates the previous versions published in 1984, 1991, 1998, and 2002. Revision of the statement was deemed necessary for multiple reasons: 1) Major studies have been reported that have advanced our knowledge of the natural history of bradyarrhythmias and tachyarrhythmias, which may be treated optimally with device therapy; 2) there have been tremendous changes in the management of heart failure that involve both drug and device therapy; and 3) major advances in the technology of devices to treat, delay, and even prevent morbidity and mortality from bradyarrhythmias, tachyarrhythmias, and heart failure have occurred

Initial and Secondary ST-T Alternans During Acute Myocardial Ischemia in the In-Situ Pig Heart

The factors responsible for the ST-T wave alternans (STTA) and associated arrhythmias during acute ischemia have not been clarified.In acutely ischemic porcine myocardium, we recorded transmural unipolar and bipolar electrocardiograms and mid-myocardial extracellular K(+) ([K(+)]e) from the center of the ischemic zone during 8-minute episodes of ischemia. Two different STTAs occurred. The initial STTA, which occurred at 4 minutes 15 seconds ± 12 seconds of ischemia during sinus rhythm, was most prominent in the subendocardium, independent of [K(+)]e and activation block, and heart rate dependent. It occurred in 13/19 (68%) occlusions at heart rates ≤ 100 bpm and in 22/23 (96%) at > 100 bpm. The second STTA was more obvious and greatest in the subepicardium. It began in the later phase of ischemia and was also heart rate dependent (5/19 [26%] occlusions at heart rates ≤ 100 bpm and 10/23 [44%] at > 100 bpm). This STTA was consistently associated with 2:1 change in the bipolar electrogram morphology, possibly due to 2:1 conduction block. Ventricular fibrillation (VF) occurred only at > 100 bpm.The initial STTA may be independent of conduction abnormalities and represent primary repolarization alternans. The second STTA may be secondary to and indicative of 2:1 activation block or marked alternans of the action potential amplitude/duration. The associated VF most likely reflects the underlying conduction abnormality