Simultaneous atrial and ventricular electrogram transmission via a specialized single lead system

Functional characterization of atrial electrograms in sinus rhythm delineates sites of parasympathetic innervation in patients with paroxysmal atrial fibrillation

OBJECTIVES

This study sought to characterize left atrial (LA) sinus rhythm electrogram (EGM) patterns and their relationship to parasympathetic responses during atrial fibrillation (AF) ablation.

BACKGROUND

The mechanistic basis of fractionated LA EGMs in patients with paroxysmal AF is not well understood.

METHODS

We analyzed 1,662 LA ablation sites from 30 patients who underwent catheter ablation for paroxysmal AF. Pre-ablation EGM characteristics (number of deflections, amplitude, and duration) were measured in sinus rhythm. Parasympathetic responses during radiofrequency application (increase of atrial-His interval by > or =10 ms or decrease of sinus rate by > or =20%) were assessed at all sites. We also prospectively studied the effect of adenosine, a pharmacological agent mimicking acetylcholine signaling in myocytes, on LA EGMs. Finally, we performed mathematical simulations of atrial tissue to delineate possible mechanisms of fractionated EGMs in sinus rhythm.

RESULTS

A specific pattern of pre-ablation sinus rhythm EGM (deflections > or =4, amplitude > or =0.7 mV, and duration > or =40 ms) was strongly associated with parasympathetic responses (sensitivity 72%, specificity 91%). The sites associated with these responses were found to be located mainly in the posterior wall of the LA. Adenosine administration and mathematical simulation of the effect of acetylcholine were able to reproduce a similar EGM pattern.

CONCLUSIONS

Parasympathetic activation during AF ablation is associated with the presence of pre-ablation high-amplitude fractionated EGMs in sinus rhythm. Local acetylcholine release could potentially explain this phenomenon.

A technique for conducting noninvasive cardiac electrophysiology studies in conscious swine

A noninvasive method was developed in swine for conducting cardiac electrophysiology (EP) studies without the potential confounding effects of sedatives or anesthetics. Following a 1-week conditioning regimen in the EP laboratory, 1-month-old Hanford miniature swine underwent transvenous pacemaker (PM) implantation under isoflurane anesthesia. Two bipolar screw-in pacing leads were inserted into the left external jugular vein, with one positioned in the right atrial appendage and one in the myocardium at the right ventricular apex. The leads were attached to a multiprogrammable pulse generator, and the pacing system was placed in a subcutaneous pocket. At weekly intervals following implantation, conscious, unsedated swine were remained in a sling for noninvasive programmed stimulation (NIPS) using a programmable telemetry system. A NIPS protocol to induce arrhythmias was performed separately for the atrium and ventricle. Data for this model are reported. Complications occurred in 6 of 26 animals studied and included one infection of the PM pocket, three cases of dislodgement of the atrial lead, and rotation of the generator within the pocket in two animals, preventing communication with the PM. This technique has been used to perform EP studies successfully in swine and has been utilized in a variety of studies of the cardiac conduction system.

Utility of the atrial endocardial electrogram concurrent with dual-chamber pacing in the determination of a pacemaker-mediated arrhythmia

A 73-year-old male required a permanent pacemaker for complete heart block. After placement of the dual-chamber pacemaker, the patient developed random, repetitive ventricularly paced coupling at the upper rate limit. The diagnosis made from the surface electrocardiography was one of ventricular tracking of occult (T wave obscured) atrial ectopic activity. Examination of the telemetered atrial electrogram (EGM) revealed a diagnosis of intermittent far-field atrial sensing of the terminal ventricular depolarization. The value of obtaining an atrial electrogram during dual-chamber pacing is discussed.

A transcardiac lead system for identification and termination of supraventricular and ventricular tachycardia

The value of a transcardiac lead system (coronary sinus to right ventricular apex) to record atrial and ventricular electrical activity and its pacing capabilities was assessed in 20 patients with a variety of tachycardias (atrial tachycardia in 3 patients, atrial flutter in 4, intranodal tachycardia in 6, circus movement tachycardia using an accessory pathway in 1 patient, and ventricular tachycardia in 9). The transcardiac lead invariably showed both atrial and ventricular electrical activity during sinus rhythm and tachycardias, allowing application of the same criteria as used when analyzing cardiac rhythm on the surface electrocardiogram. Atrial complexes had a mean amplitude of 4.2 mV during sinus rhythm and varied from 3.0 to 4.1 mV during the different types of tachycardia. Ventricular complexes had a mean amplitude of 9.8 mV during sinus rhythm, 13.8 mV during supraventricular tachycardia and 16.1 mV during ventricular tachycardia. The duration of the QRS complex on the transcardiac lead was equal to the duration of the QRS complex on the surface electrocardiogram during tachycardias with a small or wide QRS complex. By varying the intensity of current delivered through the transcardiac lead, only right ventricular pacing (mean current intensity 1.2 +/- 0.4 mA) or simultaneous atrioventricular pacing (mean current intensity 4.7 +/- 3.3 mA) could be achieved. Termination of all episodes of tachycardia was achieved with either ventricular pacing or simultaneous atrioventricular pacing. This transcardiac lead system allows clear identification of atrial and ventricular events, is suitable for tachycardia analysis using simple surface electrocardiographic algorithms and allows pacing termination of a variety of tachycardias.