Isoproterenol induced cardiovascular hypersensitivity in nonpheochromocytoma patients with paroxysmal hyperadrenergic symptoms

The objective of this study was to determine whether graded isoproterenol i nfusion test identifies a specific hypersensitivity response of the LV dias tolic relaxation properties in nonpheochromocytoma patients with paroxysmal symptoms of hyperadrenergic surges. We hypothesized that patients with hyp eradrenergic surges, nor due to pheochromocytoma, have hypersensitivity of cardiac beta-adrenergic receptor responses to exogenous catecholamines, res ulting in enhancement of LV relaxation. We assessed the physiological PI an d pa receptor responsiveness to graded isoproterenol infusion (0.01, 0.02, 0.03 and 0.04 mu g/kg per min) in 32 patients presented with hyperadrenergi c surges not due to pheochromocytoma. Two major observations rt ere made. F irst, systemic hemodynamic evaluation using 99mTechnetium first pass method revealed hyperkinetic state only in 21 patients (20 females and 1 male; ag ed 31 +/- 9 years); the other 11 patients were without hyperkinetic circula tory state (10 females and 1 male; aged 41 +/- 9 gears). At baseline, plasm a catecholamines rr ere not significantly different between the two groups. The baseline corrected LV peak filling and ejection rates (cPFR and cPER) were significantly higher in hyperkinetic group (cPFR: 10 +/- 2 vs 8 +/- 2 X 10(-2) Hz/ms, P = 0.03; cPER: 11 +/- 2 vs 8 +/- 1 X 10(-2) Hz/ms, P = 0.0 02) and their baseline HR was faster (85 +/- 16 vs 70 +/- 9 beats/min, P = 0.006). Second, the cardiac and vascular responses to isoproterenol infusio n rs ere compared between these two groups. During the graded isoproterenol infusion, the response of HR, systolic, and diastolic BP were not signific antly different between the two groups at all doses of isoproterenol, but c PFR and cPER had a more marked response to the lowest dose of 0.01 mg/kg pe r min in the hyperkinetic group. Thus, the graded isoproterenol infusion te st can differentiate between two groups of nonpheochromocytoma patients pre senting with paroxysmal symptoms of hyperadrenergic surges. Only patients w ith baseline hyperkinetic hemodynamic profile had accentuated cardiac hyper responsiveness to a low dose of isoproterenol. We concluded that cPFR and c PER is a more sensitive index to assess the response to isoproterenol, beca use of metabolic determinants affecting the rate of change in LV volume.