Diagnostic Implications of Atrial Vulnerability*

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Abstract
Extrastimulation in the atrial vulnerable zone may result in atrial fibrillation or flutter (AFF), especially with stimulation of multiple atrial sites. However, the clinical relevance of such vulnerability to AFF is unknown. Therefore, single twice-threshold extrastimuli were applied at three disparate right atrial sites in 45 consecutive unmedicated patients without overt heart failure. Group I consisted of 12 patients with documented spontaneous paroxysms of AFF. AFF was duplicated in 9 to 12 patients using extrastimulation in the vulnerable zone (5 in sinus rhythm, 4 requiring atrial pacing at 120 beats/min). Group II consisted of 33 patients without documented AFF dispite monitoring. Vulnerability to AFF was found in 12 of 33 patients (4 in sinus rhythm, 8 requiring atrial pacing). The duration of induced AFF did not discriminate between the two groups. Among the 12 Group II patients vulnerable to AFF, 3 had rapid palpitations, 2 had undiagnosed rapid tachycardias, 1 had atrial tachycardias and 1 junctional tachycardias. In vulnerable patients, the pause after AFF correlated with the pause after atrial pacing, but only 1 of 11 Group II patients with sick sinus syndrome was vulnerable. Thus, paroxysmal AFF may be duplicated with the extrastimulus technique if sufficient arial sites are stimulated, providing a model for evaluation of these arrhythmias. But atrial vulnerability, even to extrastimulation at normal heart rates, may be seen in patients suspected of atrial tachyarrhythmia in the absence of documented AFF, and does not contribute to the diagnosis of sinoatrial dysfunction.