Plasma ANP and cyclic GMP levels versus left ventricular performance at different AV delays in AV sequential pacing

Eleven resting patients with an implanted DDD pacemaker were studied. After 30 minutes of AV sequential pacing at a rate of 80 beats/min with three consecutive atrioventricular delays (AVDs; 100, 150, and 200 msec) peripheral venous blood was drawn for further analyses by specific radioimmunoassays of atrial natriuretic peptide (ANP) and the ANP second messenger, cyclic guanosine monophosphate (cGMP). Relative changes in left ventricular (LV) stroke volume following alterations of AVD were assessed by means of pulsed-Doppler echocardiography through measurement of LV outflow time-velocity integrals (TVI). The optimal AVD (oAVD) was defined in individual patients as that which was associated with the greatest TVI and with improvement over both other AVDs of more than 4%. The oAVD was found in nine patients. For these nine patients no significant differences in either plasma ANP or cGMP between various AVDs were observed. However, we found such differences with respect to values measured at oAVD; both ANP and cGMP levels were lowest at oAVD. Pooling together the data obtained in 11 patients at three AVDs, a positive correlation between ANP and cGMP levels was found (r = 0.7, P < 0.0001, n = 33). Moreover, changes of plasma ANP and cGMP induced by every AVD increment of 50 msec were also correlated (r = 0.6, P < 0.01, n = 22). It is concluded that in AV sequential pacing at rest plasma ANP reaches minimal levels at the AVD, which provides the best LV performance. Although levels of cGMP changed in parallel with those of ANP, low relative values of cGMP differences may limit the usefulness of cGMP assays in optimization of the AVD.