Comparison of vasodilator drug prazosin with digoxin in aortic regurgitation

Vasodilator therapy in patients with aortic insufficiency: a systematic review

BACKGROUND

The use of vasodilators to improve long-term outcomes in asymptomatic patients with chronic aortic insufficiency (AI) is controversial.

METHODS

We reviewed MEDLINE, PREMEDLINE, Current Contents, and Cochrane databases to identify relevant clinical trials on asymptomatic patients with chronic AI of at least moderate severity. We included those studies that involved long-term vasodilator therapy (including hydralazine, calcium-channel blockers, and angiotensin-converting enzyme inhibitors) and assessed either hemodynamic and structural parameters or clinical outcomes. Data on patient demographics, study protocols, and outcomes were abstracted.

RESULTS

Ten studies with 544 asymptomatic patients with chronic AI were identified. Treatment duration with vasodilators ranged from 12 weeks to 7 years. Of these, 8 studies compared vasodilators with placebo or no therapy, with 5 demonstrating improvements in at least 1 hemodynamic or structural parameter with vasodilators and 3 showing little or no apparent benefit. The remaining 2 studies directly compared outcomes between 2 different vasodilators. Both of these studies demonstrated greater improvements in hemodynamic and structural parameters with angiotensin-converting enzyme inhibitors compared with hydralazine and nifedipine. Clinical outcomes were primarily reported in only 2 of the 10 studies. Although one study suggested that the use of vasodilators slowed the rate of progression to surgery for aortic valve replacement, another showed no difference.

CONCLUSIONS

Vasodilators inconsistently improve hemodynamic and structural parameters in asymptomatic patients with chronic AI. In addition, the impact of vasodilators on clinical outcomes is largely uncertain and requires further study.

Are vasodilators still indicated in the treatment of severe aortic regurgitation?

Aortic regurgitation (AR) is a valve disease that causes severe complications and reduces life expectancy. Surgical correction is required in the late stages of the disease. In less advanced forms, treatment with vasodilators is a consideration. The available evidence suggests that this type of treatment has a favorable effect on the consequences of AR, particularly left ventricular remodeling. However, the impact of vasodilators on clinical endpoints complicating the course of AR remains in doubt. The limited evidence supporting or opposing the utilization of vasodilators in AR hinders drawing firm conclusions and emphasizes the process of individualized interpretation of the clinical presentation of patients with the disease.

Vasodilatation with felodipine in chronic asymptomatic aortic regurgitation

BACKGROUND

Afterload reduction decreases volume overload on the left ventricle and may thereby delay the need for valve replacement in chronic asymptomatic aortic regurgitation. The aims of this randomized double-blind, placebo-controlled trial were to examine short- and long-term hemodynamic effects of felodipine in chronic asymptomatic aortic regurgitation.

METHODS

Sixteen patients were randomly assigned to an intravenous infusion of either felodipine 0. 3 mg or placebo followed by 3 months' treatment with felodipine 10 mg or placebo orally once daily. Magnetic resonance imaging was performed at baseline, immediately after intravenous treatment, and after 3 months of oral treatment.

RESULTS

Intravenous felodipine caused a statistically significant reduction in the systemic vascular resistance from (mean +/- SD) 1160 +/- 400 to 970 +/- 320 dynes. s. cm(-5) (P <.05), in the regurgitant volume index from 1.5 +/- 0.8 to 1.3 +/- 0.8 L. min(-1). m(-2) (P <.05), and in the regurgitant fraction from 0.31 +/- 0.15 to 0.26 +/- 0.14 (P <.05). The forward cardiac output index increased significantly from 3.2 +/- 0.9 to 3.5 +/- 0.7 L. min(-1). m(-2) (P <.05). Three months of oral treatment with felodipine caused a corresponding but more pronounced decrease in systemic vascular resistance of 880 +/- 330 dynes. s. cm(-5) (P <.05), regurgitant volume index of 1.2 +/- 0.7 L. min(-1). m(-2) (P <.05), and regurgitant fraction 0.25 +/- 0.11 (P <.05), whereas the forward cardiac output index increased to 3.6 +/- 0.7 L. min(-1). m(-2) (P <.05). No significant changes were found in the placebo group. Left ventricular volumes and ejection fraction remained unaffected by treatment, but compared with the placebo group left ventricular myocardial mass decreased significantly from 137 +/- 24 to 132 +/- 21 g. m(-2) (P <.01).

CONCLUSION

In chronic asymptomatic aortic regurgitation, felodipine causes beneficial hemodynamic effects that may postpone the need for valve replacement.

Effects of six-month afterload reduction therapy with hydralazine in chronic aortic regurgitation

Seventeen patients with chronic asymptomatic aortic regurgitation (AR) were studied to determine whether 6 months of hydralazine therapy can reduce the severity of AR or reverse left ventricular (LV) enlargement and hypertrophy. Echocardiography, radionuclide angiography at rest and during exercise, and maximal treadmill exercise with respiratory gas analysis were performed at intake and after a 6-month double-blind treatment period. After dose titration with hydralazine, patients were randomized to their maximal tolerated hydralazine dose or to placebo. At intake, hydralazine and placebo groups were similar. Six patients taking hydralazine and 8 taking placebo completed the study protocol. One patient taking placebo died and 2 patients taking hydralazine withdrew with drug-related adverse effects. The mean titrated dose of hydralazine was 96 +/- 9 mg, but the mean treatment dose was 63 +/- 21 mg administered 3 times daily because of drug intolerance. After 6 months, mean systolic blood pressure with hydralazine therapy decreased from 136 to 125 mm Hg (p less than 0.02), and end-systolic posterior wall thickness increased from 1.58 to 1.70 cm (p less than 0.05), resulting in a significant reduction in M-mode meridional end-systolic stress (from 104 to 80 kdynes/cm2) (p less than 0.05). M-mode fractional shortening increased from 0.28 to 0.31 (p less than 0.05) with hydralazine, but mean LV echocardiographic dimensions were unchanged. LV mass increased from 383 to 434 g (p less than 0.05) with hydralazine primarily because of an increase in end-diastolic wall thickness. In the placebo group, there was no change in any of the hemodynamic or echocardiographic parameters at 6 months.(ABSTRACT TRUNCATED AT 250 WORDS)

Unloading effects of prazosin in patients with chronic aortic regurgitation

Seventeen patients with chronic aortic regurgitation (AR) were examined by echocardiography and left and right heart catheterization. Cardiac output and regurgitation volume were measured by the dye dilution method. Administration of single and four repeated doses of prazosin (PZ) led to reductions of left ventricular (LV) end-diastolic, end-systolic, and left atrial end-systolic diameters, and decrease of left ventricular filling pressure. Regurgitation fraction, regurgitation flow, and volume indexes decreased significantly (p less than 0.01). Total left ventricular output decreased (p less than 0.001) as did derived parameters of left ventricular work and performance. Fractional shortening, ejection fraction, and mean circumferential fiber shortening velocity increased as did LV dP/dt and dP/dt/P. Changes in heart rate and cardiac and stroke indexes after PZ were not significant. Preload reduction (dilation of the venous bed and reduction of regurgitation) seems to be the most important effect of PZ in AR. We found PZ to be a suitable and effective drug for oral treatment of chronic AR.

Prazosin update. A review of its pharmacological properties and therapeutic use in hypertension and congestive heart failure

Prazosin is an orally active post-synaptic selective alpha 1-adrenoreceptor antagonist that has been widely used in treating hypertension and congestive heart failure (CHF). Its role in the treatment of hypertension has previously been reviewed in this journal. Subsequent reports confirm its efficacy in treating mild to severe hypertension as a single agent or, more frequently, in combination with another antihypertensive agent and/or a diuretic. Recent studies of the metabolic effect of prazosin indicate that the drug may have a favourable effect on plasma lipids in hypertensive patients. Its recent use in treatment of congestive heart failure has shown prazosin to be comparable with nitroprusside in producing balanced arterial and venous dilation with generally sustained haemodynamic and clinical effects during long term therapy. Initial studies in Raynaud's phenomenon and in patients with aortic regurgitation or aortic stenosis or with mitral regurgitation are promising, but require confirmation from wider clinical experience. The drug has generally been well tolerated. The primary side effect of orthostatic hypotension can be largely avoided by beginning treatment with a low dose.

Noninvasive assessment of left ventricular wall stress in chronic congestive heart failure patients

Therapy with prazosin can improve the condition of patients with congestive heart failure due to its vasodilating action. Therefore nine patients with volume overloaded left ventricles due to aortic insufficiency and mitral insufficiency received 1 mg. of prazosin four times a day for two weeks. Peak and end-systolic wall stress were estimated using a noninvasive echocardiographic technique. The peak systolic wall stress in this group was 155 x 10(3) dynes/cm2 which is similar to the reported normal value. However, the end systolic wall stress was 101 x 10(3) dynes/cm2 which is much higher than the reported normal values. Following the administration of oral prazosin, the end systolic stress was normalized while the peak systolic stress was reduced below normal. As a result of therapy with prazosin, the ejection fraction, the percentage of change in the minor axis, and the velocity of circumferential fiber shortening significantly increased. Thus, the oral administration of prazosin can improve left ventricular function in patients with mitral insufficiency and aortic insufficiency.

Afterload reduction with nifedipine in aortic insufficiency

The acute hemodynamic effects of nifedipine were assessed in 12 patients with severe aortic insufficiency during control conditions and 30 minutes after administration of nifedipine (20 mg sublingually). Left ventricular end-diastolic pressure decreased from 19 +/- 8 (mean +/- standard deviation) to 9 +/- 5 mm Hg (probability [p] less than 0.0001), mean aortic pressure from 98 +/- 12 to 80 +/- 9 mm Hg (p less than 0.00001), systemic vascular resistance from 1,135 +/- 280 to 794 +/- 176 dynes . s. cm-5 (p less than 0.0002) and rate-pressure product from 11,732 +/- 1,727 to 10,022 +/- 1,103 mm Hg beats/min (p less than 0.01). Forward cardiac index increased by 24 percent, from 3.8 +/- 1.1 to 4.4 to 0.8 liters/min per m2 (p less than 0.04). Left ventricular end-diastolic volume, ejection fraction and total stroke work index did not change significantly. Regurgitant fraction, measured in five patients, changed parallel with systemic vascular resistance. Left ventricular function was maintained while both preload and afterload were decreased. Regurgitant flow was moderated and myocardial oxygen demand decreased. This hemodynamically favorable condition, due to nifedipine, is clinically important and suggests the need for further therapeutic trials.

Captopril in congestive heart failure

1 Vasodilator therapy is used widely for the treatment of congestive heart failure irrespective of its origin. The acute and long-term effects of captopril were studied in 50 patients with congestive heart failure due to valvular incompetence, hypertension, cardiomyopathy, and ischaemic heart disease. Haemodynamic studies were performed in all patients. In those with valvular incompetence, regurgitation fractions were measured cineangiographically. In patients with ischaemic heart disease coronary sinus blood flow was assessed by a thermodilution technique. During clinical follow-up patients were studied by non-invasive techniques including electrocardiography, echocardiography and chest radiography.

2 In the short-term studies, left ventricular filling pressure, total peripheral resistance, and end-diastolic and end-systolic volumes decreased after captopril, while cardiac output, stroke volume, and ejection fraction increased. Valvular regurgitation fraction was assessed in 10 patients with aortic or mitral insufficiency. In every patient the regurgitation fraction decreased. Coronary blood flow was measured in eight patients with severe ischaemic heart disease. In three patients it remained constant and in the other five patients it decreased. At the same time a highly significant decrease of myocardial oxygen consumption was measured.

3 During long-term treatment clinical improvement occurred in most of the patients. This was documented by a reduction of ventricular diameters in hypertensive heart disease as well as in valvular incompetence. These values remained constant in congestive cardiomyopathy despite clinical improvement. Serious hypotensive episodes were observed in eight patients with valvular stenosis or complex congenital cardiac abnormalities.

4 Captopril is therefore an effective vasodilator for the treatment of congestive heart failure. In patients with intact left ventricular function captopril should not be given because severe hypotensive episodes may occur. Ischaemic heart disease with congestive heart failure is no contraindication for treatment with captopril because the reduction in myocardial blood flow is balanced by the reduced myocardial oxygen consumption.

Comparative pharmacology and clinical efficacy of newer agents in treatment of heart failure

The animal and human pharmacology of several new drugs (prazosin, trimazosin, pirbuterol, and carbazeran) useful in the treatment of congestive heart failure (CHF) is delineated in relation to the pharmacology of other agents employed for CHF management. Prazosin and trimazosin are selective alpha 1-blockers that cause a balanced increase in cardiac output (CO) and reduction in left ventricular filling pressure (LVFP); the reduction in diastolic blood pressure with these drugs is significantly related to increase in treadmill exercise, fall in LVFP, and increase in CO. Pirbuterol is a relatively selective beta 2-agonist with somewhat greater effects on CO than on LVFP. Early promise in CHF therapy is being shown by a novel series of cyclic adenosine monophosphate (cAMP) phosphodiesterase inhibitors with combined direct inotropic and vasodilator effects. Double-blind long-term studies demonstrate persistent efficacy of prazosin and trimazosin in CHF as measured by improvement in New York Heart Association functional class, treadmill exercise performance, and noninvasive measures of cardiac function; these data are supported by studies in which repeat cardiac catheterization has been performed after several months of therapy. Double-blind studies of other CHF drugs are in progress.