RELATION BETWEEN CYCLE LENGTH, VOLUME, AND PRESSURE IN TYPE-I ATRIAL-FLUTTER

Assuming that type I atrial flutter is a macroreentrant circuit, its c ycle length should vary with the atrial dimensions. In order to test t his hypothesis, flutter cycle length was measured while inducing atria l volume and pressure changes by postural and pharmacological means in seven patients undergoing a therapeutic programmed stimulation for ty pe I atrial flutter conversion. Right atrial volume was estimated from B-mode echocardiography data. Basal values were compared with those o btained during inspiration, expiration, Valsalva maneuver, negative ti lt (head down), and positive tilt (head up) with 0.8-1.6 mg p.o. nitro glycerin. The right atrial size increased slightly from 17.8 to 18.3 c m2 (p = 0.04) during the pressure load induced by negative tilt (+ 3 m mHg), with a corresponding lengthening of the flutter cycle length fro m 228 to 233 msec (P = 0.02). Similarly, pressure unloading of -2 mmHg by positive tilting and nitrates was accompanied by a decrease in rig ht atrial size to 16.6 cm2 (p = 0.04), with a corresponding decrease i n cycle length from 228 to 219 msec (P = 0.03). Respiratory maneuver y ielded similar results with an inspiratory cycle lengthening, expirato ry shortening, and further shortening during Valsalva maneuver. These experiments demonstrate a direct relation between cycle length and atr ial volume in human type I atrial flutter. They underline the importan ce of the right heart preload and atrial size for the electrophysiolog ical characteristics of type I atrial flutter. Beside its fundamental interest, this finding is important for the understanding of the mecha nism of maintenance and therapeutic responses of this common arrhythmi a.