Role of cycle length, cycle length alternans, and electrocardiographic lead in electrical alternans with rapid atrial pacing

The role of cycle length and cycle length alternans in the induction of tachycardia-related QRS electrical alternans was investigated using an atrial pacing protocol in 16 patients. Pacing was performed at a cycle length less than 400 ms in 5 patients, greater than 400 ms in 5 and at both in 6 with 0, 6, 10, 20, 40 and 60 ms of atrial cycle length alternans. A 12-lead electrocardiogram and high right atrial, His bundle and right ventricular apical electrograms were simultaneously recorded after 30 to 60 seconds of pacing. Alternans was produced in 88% of patients. Alternans was 3 times more frequent at short (less than 400 ms) than long paced cycle lengths (greater than 400 ms) (66% vs 22%, p less than 0.0001). Alternans increased with increasing cycle length alternans and occurred with very little (less than or equal to 10 ms) atrioventricular nodal, His-Purkinje and ventricular cycle length alternans when paced cycle length was short. Alternans was more frequent in the precordial than the limb leads (45% vs 17%, p less than 0.001) and was most frequent in V3 and V2 (sensitivity 69% and 65%) and least frequent in leads I and aVL (sensitivity 4% and 10%). More leads per electrocardiogram showed alternans at short compared with long paced cycle lengths and the number of leads per electrocardiogram increased with increasing cycle length alternans. Occurrence of alternans was highly related to QRS amplitude by Spearman rank correlation (p less than 0.0005).