Electrophysiologic control of ventricular rate in atrial fibrillation using automatic left vagal control of atrioventricular conduction

Matthew Scott Waninger, Purdue University

Abstract

Atrial fibrillation (AF) is a common cardiac disorder, primarily of the elderly, that now affects over one million Americans. In this condition, the normal coordinated contraction of the atrial muscle is disturbed and atrial pumping ceases. The normal synchronized electrical depolarizations and repolarizations of atrial myocardial cells are replaced by random cell depolarizations and repolarizations which generate a high-frequency electrical signal (f waves) in the atrial electrogram. These depolarizations are propagated through the atrioventricular (A-V) node to the ventricles, which respond at a rapid, irregular rate, limited by the refractory period of the A-V node. Although the atria can be defibrillated electrically, reversion to AF is common. Antiarrhythmic drugs are used to either chemically cardiovert the atria, or if unsuccessful, depress conduction across the A-V node to reduce the number of impulses conducted to the ventricles. However, drug therapy is not always successful and often has serious side effects. Radio-frequency ablation of the A-V node prevents all impulses from reaching the ventricles and a pacemaker must be implanted. There is evidence that this procedure can be thrombogenic and often multiple attempts must be made before successful ablation occurs. In this research, a new therapy for AF has been developed that employs electrical left vagal stimulation to control propagation of excitation through the A-V node. In open-loop feasibility studies, twenty-nine out of twenty-nine attempts demonstrated increasing left vagal stimulation frequency decreases ventricular rate and either reduces or completely eliminates pulse deficit. A closed-loop controller was developed to automatically adjust the vagus-nerve stimulation frequency to maintain ventricular rate within a preselected range. Records from five out of six dogs demonstrated that control of ventricular rate by this technique was possible. These episodes of control lasted from five to forty-five minutes. Sufficient control was not possible in the remaining one. System time response studies were conducted and a mathematical description of the atrioventricular nodal response to left vagal stimulation was developed. The parameters of this equation have physiologic interpretation. These animal studies have verified the soundness of the method and a United States patent has been issued for the system.

Degree

Ph.D.

Advisors

Geddes, Purdue University.

Subject Area

Biomedical research

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