Future directions in vasodilator therapy for heart failure

Angiotensin converting enzyme inhibitor therapy in severe postcardiotomy dysfunction: a prospective randomized study

BACKGROUND

Occurrence of severe postcardiotomy dysfunction requiring prolonged postoperative support with intra-aortic balloon counterpulsation (IABP) and inotropes, complicating surgery for coronary artery disease and valvular heart disease carries important hospital morbidity and mortality. This study evaluated the impact of angiotensin converting enzyme inhibitor (captopril) therapy in these patients in the early postoperative period.

METHODS

During a 5-year period, 298 patients with prolonged diminished cardiac output required support (> 48 to 72 hours) with IABP plus two or three inotropes. This cohort was randomized to two groups, group A (195 patients) who were continued on IABP and inotropes alone and group B (103 patients) who were given an angiotensin converting enzyme (ACE) inhibitor, captopril 48 to 72 hours postoperatively and continued on IABP and inotropes.

RESULTS

Tissue perfusion and hemodynamic parameters improved (p < 0.0001) in group B with early termination of IABP (duration of support mean 86 hours in group B vs 169 hours in group A) and inotropes. Peak improvement in tissue perfusion and hemodynamic parameters correlated with decreased serum angiotensin converting enzyme levels. Hospital mortality occurred in 31% of patients in group A and 14.5% in group B. Morbidity complications developed in 37% of patients in group A and 20% in group B. The average length of hospital stay in group A was 27 days and 17 days in group B. Cardiac, pulmonary, infective, gastrointestinal, renal, and neurological complications were common in both groups.

CONCLUSION

Administration of ACE inhibitors in the early postoperative period to patients with severe postcardiotomy dysfunction caused improvement in tissue perfusion with decreases in mortality, morbidity, and length of hospital stay. These drugs, by effectively limiting physiological effects induced by renin angiotensin-aldosterone axis and other mechanisms, caused recovery of stunned myocardium. More randomized trials are needed before recommending these drugs for routine use in similar patients.

Mechanisms of positive inotropic action of flosequinan, hydralazine, and milrinone on mammalian myocardium

Flosequinan is an arterial and venous dilator that also has a positive inotropic effect at relatively higher doses. The purpose of this study was to determine the mechanism of this positive inotropic effect in ferret papillary muscles loaded with the Ca2+ indicator, aequorin. Over the range of doses from 10(-6) to 10(-3) M, flosequinan produced a 61 +/- 9% increase in peak tension that was accompanied by a corresponding increase in [Ca2+]i. This positive inotropic effect was not selectively blocked by addition to the perfusate of procaine 0.6 microM, tetrodotoxin 10(-6) M or by verapamil, 5 x 10(-8) M. In contrast, the positive inotropic effect of flosequinan, but not milrinone or hydralazine, was potentiated by prior addition of ouabain 3 nM to enhance intracellular Ca2+ via reduction of the Na+/Ca2+ exchange. Moreover, antagonists of Na+/Ca2+ exchange, including cadmium 10 microM, amiloride 600 microM and choline substitution for 1/3 Na+ in the perfusate, blocked the response to flosequinan but not hydralazine or milrinone. These results indicate that flosequinan produces a positive inotropic effect by reduction of Na+/Ca2+ exchange in mammalian myocardium. Moreover, flosequinan has the potential to interact synergistically with other positive inotropic agents such as digoxin that affect Na+/Ca2+ exchange by direct or indirect actions.

Sustained hemodynamic response to flosequinan in patients with heart failure receiving angiotensin-converting enzyme inhibitors

OBJECTIVES

We evaluated the short- and long-term effects of flosequinan in 47 patients with severe heart failure despite ongoing captopril treatment.

BACKGROUND

There have been no previous evaluations of the long-term hemodynamic effects of any direct-acting vasodilator in patients with heart failure receiving an angiotensin-converting enzyme inhibitor. Flosequinan is an arterial and venous vasodilator with actions similar to those of the hydralazine-isosorbide dinitrate combination.

METHODS

After baseline hemodynamic measurements using balloon-tipped pulmonary artery and radial arterial catheters, patients were randomized to receive 50, 100 or 150 mg of flosequinan daily. Hemodynamic variables were measured immediately before and after short-term flosequinan administration and after 8 weeks of therapy.

RESULTS

With short-term flosequinan administration, mean arterial, right atrial and left ventricular filling pressures decreased by 6.4 +/- 1.1, 3.8 +/- 0.5 and 7.3 +/- 0.7 mm Hg, respectively (all p < 0.001). Cardiac index increased by 0.5 +/- 0.1 liters/min per m2, systemic vascular resistance decreased by 616 +/- 105 dynes.s.cm-5 and heart rate increased by 4 +/- 1 beats/min (all p < 0.001). After 8 weeks of long-term flosequinan administration, the vasodilator effect of a dose of flosequinan persisted. Compared with pretreatment baseline values, mean arterial, right atrial and left ventricular filling pressures at the peak effect of flosequinan were decreased by 3.5 +/- 1.3, 2.8 +/- 0.7 and 5.1 +/- 1.3 mm Hg, respectively (all p < 0.01). Systemic vascular resistance had decreased by 585 +/- 95 dynes.s.cm-5, cardiac index had increased by 0.5 +/- 0.1 liters/min per m2 and heart rate had increased by 10 +/- 2 beats/min (all p < 0.001).

CONCLUSIONS

The arterial and venous vasodilator flosequinan exerts both short- and long-term sustained hemodynamic effects in patients with heart failure receiving angiotensin-converting enzyme inhibitors.

Differential inotropic effects of flosequinan in ventricular muscle from normal ferrets versus patients with end-stage heart failure

1. In right ventricular papillary muscles from control ferrets, flosequinan (10(-7)-10(-4) M) produced a concentration-dependent positive inotropic effect (10(-5) M = 153 +/- 24, 10(-4) M = 198 +/- 44% increase in isometric tension; control tension = 100%; n = 11) associated with a corresponding increase in amplitude of the intracellular Ca2+ ([Ca2+]i) transient recorded with aequorin (10(-5) M = 133 +/- 11, 10(-4) M = 187 +/- 36% increase in [Ca2+]i transient; n = 11). 2. The positive inotropic effect of flosequinan in control ferret ventricular muscle was neither blocked by propranolol (6 x 10(-7) M), nor associated with the abbreviation of the [Ca2+]i transient and contraction that is typical of catecholamines. 3. Neither flosequinan (n = 12) nor BTS 53 554, its sulphone metabolite (n = 6) produced a positive inotropic effect or altered the time course of contraction in myocardium from the hearts of patients with end-stage failure. 4. In contrast to milrinone, which produces a positive inotropic effect via phosphodiesterase inhibition, the unresponsiveness of myopathic human myocardium to flosequinan was not restored after intracellular adenosine 3':5'-cyclic monophosphate (cyclic AMP) levels were increased by prior treatment with forskolin (n = 13). 5. Taken together, these data indicate that flosequinan has a direct positive inotropic effect that is Ca(2+)-dependent, but independent of changes in intracellular cyclic AMP concentrations. 6. The positive inotropic effect may be species-dependent or altered by the presence of hypertrophy and/or heart failure. However, when used therapeutically in patients with severe heart failure, our data suggest that flosequinan should not adversely affect myocardial oxygen consumption through direct or catecholamine-mediated actions on the heart.