Peripheral circulating levels of atrial natriuretic peptide may exhibit short-term variation compatible with a pulsatile pattern of secretion. We obtained samples every 2 min for 90 min from the antecubital vein of 16 patients with chronic cardiac failure and 13 controls. Overall levels were higher in the patients (median and quartiles 230 (125,325) vs. 26 (16,48) ng l-1; P < 0.001). In both groups there was considerable variability, with 10 (2-12) peaks, 9 (7-15) troughs (both defined as > 2 SD from the mean) and 16 (13-18) pulses (defined by computer) during the sampling period in controls, and a similar number in patients. We then carried out simultaneous sampling in the pulmonary artery, femoral artery and peripheral vein in eight subjects with normal cardiac function and six patients with impaired function due to valvular heart disease. The pattern of variability was preserved in all three sites in both groups, suggesting intermittent secretion rather than variable breakdown of the peptide in the lung. No changes in right atrial pressure or heart rate were observed to coincide with the variations, but levels of the peptide in the pulmonary artery correlated with right atrial pressure in patients (r = 0.87; P < 0.05). The mechanism of such periodicity and its pathophysiological importance remain unknown.

Impaired NO-mediated pulmonary vasodilatation does not appear to contribute to exercise limitation in CCF. Alternatively, the lower NO production observed during maximal exercise in the patient group compared with controls may reflect a reduced incremental response of a system that is already abnormally activated in heart failure.

The data demonstrate marked variability in circulating levels of the neuropeptides studied. In addition, peaks and troughs were observed every 10-15 min from all three vascular beds. If these peptides are secreted in a pulsatile pattern, then interpretations of single measurements should be guarded. Furthermore, this study raises interesting questions about the physiology of hormone secretion in man.

Using a unipolar esothoracic pacing system (where current passes from a point source positioned in the distal esophagus to a chest wall pad) and pulse duration of 50 msec, satisfactory 1:1 ventricular capture was obtained in 57 (86%) of 66 patients, with a mean threshold current of 27.7 mA at an optimal depth of 40.3 cm from the lower lip. When the unipolar esothoracic and bipolar transesophageal ventricular pacing systems were compared, the bipolar system was associated with a lower success rate and higher threshold current. When unipolar esothoracic pacing and gastrothoracic pacing (where current passes from a point source positioned in the stomach to a chest wall pad) were compared in 23 patients with bradyarrhythmia, ventricular capture was achieved using gastrothoracic pacing in 22 patients (96%) and esothoracic pacing in 21 (91%): gastrothoracic pacing required less current (16.0 mA +/- SD 7.2 vs 25.8 mA +/- SD 8.6). Optimal ventricular capture occurred using a unipolar gastrothoracic pacing electrode inserted to an average depth of 44.3 cm together with a high impedance chest pad (250 omega) placed in the fourth interspace at the left sternal edge, with 50-msec current pulses and a mean threshold of 16.0 mA. Thus, using a gastroesophageal electrode system, ventricular pacing can be achieved successfully, and the availability of such a system could play a major role in resuscitation of patients from severe bradyarrhythmias.

No abstract