Hysteresis in atrial refractoriness in the conscious dog: influence of stimulation parameters and control by the autonomic nervous system

Exploring Refractoriness as an Adjunctive Electrical Biomarker for Staging of Atrial Fibrillation

Patients diagnosed with the same subtype of atrial fibrillation according to our current classification system may differ in symptom severity, severity of the arrhythmogenic substrate, and response to antiarrhythmic therapy. Hence, there is a need for an electrical biomarker as an indicator of the arrhythmogenic substrate underlying atrial fibrillation enabling patient‐tailored therapy. The aim of this review is to investigate whether atrial refractoriness, a well‐known electrophysiological parameter that is affected by electrical remodeling, can be used as an electrical biomarker of the arrhythmogenic substrate underlying atrial fibrillation. We discuss methodologies of atrial effective refractory period assessment, identify which changes in refractoriness‐related parameters reflect different degrees of electrical remodeling, and explore whether these parameters can be used to predict clinical outcomes.

A novel implantable cardiac telemetry system for studying atrial fibrillation

Atrial fibrillation (AF) is the most common arrhythmia in clinical practice. Most in vivo experimental research on AF is performed in a surgical setting, on animals instrumented by external devices, or using commercial implantable pacemakers. This paper describes a novel implantable cardiac telemetry system, which allows the study of AF remotely in conscious and ambulatory animals over a few month period. To validate this concept, the system was built and implanted in a sheep for 3 months. During this period, the system was used to deliver chronic rapid atrial pacing for AF induction, and to record and measure atrial electrograms and atrial effective refractory period (AERP) daily. During the course of AF induction the AERP decreased, confirming the progression of the electrical remodeling process in the atria. Episodes of paroxysmal AF were successfully induced in the animal. Burst pacing therapy was delivered with the system, however, no AF termination was observed. Result shows that this telemetry-based pacing and monitoring system can be used to study AF in a conscious animal non-invasively for an extended period of time, making this system a unique research tool.

Effects of quinidine, verapamil, nifedipine and ouabain on hysteresis in atrial refractoriness in the conscious dog: an approach to ionic mechanisms

1. This work determines the effects of quinidine, verapamil, nifedipine and ouabain on the hysteresis of the atrial effective refractory period (AERP) in the conscious dog. 2. AERP was always longer in the increasing phase than in the decreasing phase of the extrastimulus method, thus demonstrating the existence of AERP hysteresis. Calculated as the difference between the two values, hysteresis was between 8+/-0.8 and 11+/-1.0 msec. 3. Quinidine increased hysteresis from 9+/-0.7 to 13+/-0.7 msec, whereas verapamil decreased it from 10+/-0.9 to 5+/-0.5 msec and nifedipine did not affect it. Ouabain also lengthened hysteresis from 8+/-0.8 to 11+/-1.2 msec. 4. Thus, these results confirm the existence of a hysteresis phenomenon in the AERP in the conscious dog and are evidence that the fast sodium and slow calcium specific membrane currents participate in this phenomenon.