Contrasting preload-dependent hemodynamic and neurohumoral effects of isomazole, a partial phosphodiesterase inhibitor and calcium sensitizer.

Background: Currently evaluated positive inotropic agents that act predominantly through phosphodiesterase III-inhibiting properties, have been disappointing in the treatment of heart failure. Lack of efficacy as a result of diminished cellular cyclic adenosine monophosphate and vasodilating tolerance and side effects are prevalent. In contrast, calcium sensitization is preserved in heart failure and agents that combine phosphodiesterase-inhibiting and calcium-sensitizing properties may be more efficacious. Isomazole is such a novel agent with combined properties. This study investigated the acute hemodynamic and neurohormonal effects of intravenous isomazole (3 micrograms/kg/min for 30 minutes).

Methods And Results: The effects of preexisting preload were evaluated in 18 patients with heart failure, New York Heart Association class II/III, and elevated (> 15 mmHg, n = 11, group I) and normal; (n = 7, group II) pulmonary wedge pressure at baseline. In the overall group, isomazole increased myocardial contractility and relaxation and decreased systemic resistance by 20%. Left and right filling pressures fell by 35-45%, accompanied by a 69% reduction in cardiac atrial natriuretic peptide release. In contrast, levels of arterial norepinephrine and renin both increased by 27%. Cardiac output increased in group I (23%), but fell in group II (18%), accompanied by a 51% increase in arterial norepinephrine. Cardiac atrial natriuretic peptide decreased in group I, but not in group II.

Conclusions: Isomazole induced positive inotropic and lusitropic effects and arterial vasodilation in all patients. Cardiac pump function improved only in group I, accompanied by a reduction in sympathetic activity and renin-angiotensin and aldosterone levels and a more pronounced decrease in cardiac atrial natriuretic peptide release. In contrast, in patients with normal to low preload, the further reduction in preload led to a deterioration of pump function and increased sympathetic tone.