BASE-LINE ARTERIAL-PRESSURE AFFECTS SYMPATHOEXCITATORY RESPONSES TO VENTRICULAR PREMATURE BEATS

The seconds to minutes before sudden cardiac death are characterized b y fluctuations of arterial pressure, cardiac rhythm, and probably symp athetic nerve activity. We explored the interrelations among these fac tors in seven patients undergoing clinical electrophysiological testin g. We measured muscle sympathetic nerve activity (SNA) and arterial pr essure responses to ventricular premature beats induced throughout the cardiac cycle under three conditions: 1) lowered arterial pressure an d elevated SNA produced by intravenous nitroprusside, 2) baseline arte rial pressure and SNA during saline infusion, and 3) elevated arterial pressure and decreased SNA activity produced by intravenous phenyleph rine. Sympathetic responses to premature beats were inversely related to diastolic pressure. The magnitude of the sympathetic response was d irectly related to the prevailing arterial pressure and inversely rela ted to baseline SNA. These data demonstrate that sympathoexcitation ev oked by ventricular dysrhythmias is determined importantly by the prev ailing arterial pressure and possibly by the background R-R interval a nd level of sympathetic activity. This effect may influence hemodynami c and electrophysiological stability during dysrhythmias.