Comparative hemodynamic effects of intravenous nitroprusside and oral prazosin in refractory heart failure

Acute effects of alpha- and beta-adrenoceptor blockade on plasma atrial natriuretic peptides during exercise in elderly patients with mild hypertension

In a randomized study in 26 elderly patients with mild essential hypertension, acute effects of alpha- and beta-adrenoceptor blockade on plasma ANP levels were examined at rest and during ergometric exercise. Plasma ANP level and LVEF were measured before and after administration of prazosin (an alpha 1-adrenergic blocker), atenolol (a cardioselective beta-adrenergic blocker), or carteolol (a nonselective beta-adrenergic blocker). Plasma ANP level was increased by exercise. Carteolol and atenolol increased plasma ANP levels at rest and during exercise, but the effect of atenolol was not statistically significant. Prazosin significantly suppressed the ANP values at rest and during exercise. The LVEF was increased by prazosin and decreased by beta-blockers, especially by carteolol. Multivariate regression analysis showed that LVEF was the most significant predictor of the plasma ANP level at maximal exercise; the resting blood pressure and heart rate were not predictors of this value. The results showed that single administrations of an alpha-blocker and a nonselective beta-blocker had opposite effects on the plasma ANP level both at rest and during exercise in elderly patients with mild essential hypertension. The observed difference in the ANP response seems to be related to changes in left ventricular function rather than changes in blood pressure or heart rate.

The hemodynamic and clinical responses to terazosin, a new alpha blocking agent, in congestive heart failure

To determine the hemodynamic effects of a new alpha 1 blocker, terazosin, in congestive heart failure, six patients with this condition underwent hemodynamic testing (at rest and during exercise) before and after dosing. Doses of 2, 5, and 10 mg were examined in sequence over 3 days to define dose-response characteristics. Terazosin, in these doses, decreased pulmonary and systemic vascular resistances and right atrial and pulmonary capillary wedge pressures. Terazosin increased stroke volume and cardiac output, presumably through afterload-reduction, without altering heart rate. These aforementioned responses were apparent both at rest and during exercise. While a direct relationship existed between dose and plasma concentration, a similar relationship was not observed for dose (or plasma concentration) and hemodynamic response; no differences were noted between the hemodynamic responses to the three doses. Improvement in hemodynamics persisted and the clinical status and exercise capacity improved in the four patients chronically treated (over 2 months) with terazosin. Treating the heightened tone of the sympathetic nervous system in congestive heart failure with the alpha 1 blocker, terazosin, may be of benefit to some patients afflicted with this disorder.

Role of vasodilators in the treatment of congestive heart failure

Appreciation of the important role played by peripheral vasoconstriction in the pathophysiology of congestive heart failure (CHF) has led to the widespread use of vasodilators as treatment. Short-term studies show that, regardless of the vasodilator used, the arterial and venous dilatation produced invariably results in improvement in the hemodynamic status of patients. This short-term response, however, does not automatically translate to long-term clinical improvement. The reasons for this are not well understood but such factors as differing mechanisms of action, development of tolerance and unique patterns of regional redistribution of blood flow may all play a modifying role in differentiating one vasodilator from another. Nevertheless, a number of controlled trials have demonstrated sustained symptomatic and functional improvement when vasodilators such as the converting enzyme inhibitors or nitrates are given to patients with CHF.

New concepts and drugs in the treatment of congestive heart failure

This article seeks to make clear the basic differences in the treatment of heart failure between therapeutic maneuvers that are aimed at improving the mechanical loading conditions of the heart and those that are aimed at augmenting the fundamental contractile or inotropic state of the myocardium. Emphasis is placed on recognizing that treatment expectations must be viewed within an age- or maturity-dependent framework, since a diminished margin of cardiocirculatory reserve exists in the smallest and youngest patients that limits the extent of benefit that may be derived from diverse treatment approaches.

Haemodynamic effects of a single low dose of prazosin in patients with chronic congestive cardiac failure correlations with pharmacokinetics

The haemodynamic effects and pharmacokinetics of a single orally administered dose of 0.5 mg of prazosin have been compared in six patients with stable severe congestive cardiac failure. Administration of prazosin induced significant decreases in mean pulmonary capillary wedge pressure (from 27.5, s.e.m. = 4.5 to 19.4, s.e.m. = 5.1 mmHg; P less than 0.001), mean arterial blood pressure (from 94.5, s.e.m. = 6.0 to 85.4, s.e.m. = 5.0 mmHg; P less than 0.01), and systemic vascular resistance (from 1690, s.e.m. = 360 to 1420, s.e.m. = 200 dyn. s/cm5; P less than 0.05) and a rise in cardiac index from 1.98 (s.e.m. = 0.07) to 2.28 (s.e.m. = 0.16) litres/min per m2 (P less than 0.05). There was a non-significant fall in heart rate. Pharmacokinetic analysis revealed maximum plasma prazosin concentrations of 4.1 (s.e.m. = 1.4) ng/ml, occurring 2.1 (s.e.m. = 0.4) h after drug ingestion. The mean elimination half-life was 5.1 (s.e.m. = 0.8) h, which is longer than that found in our previous studies in normal subjects. There was considerable interindividual variation in peak plasma prazosin concentrations, elimination half-life and area under the concentration-time curve. While mean maximal haemodynamic effects of prazosin occurred at similar times to the peak plasma concentration of the drug, there was no significant correlation between the extent of haemodynamic response and individual pharmacokinetic parameters. It is concluded that significant and potentially beneficial haemodynamic effects occur with the initial administration of 0.5 mg oral dose of prazosin in patients with stable congestive cardiac failure and it is suggested that in many patients little advantage will be achieved with higher initial doses.

Vasodilator therapy in chronic congestive heart failure

Vasodilator agents are relatively new additions to the armamentarium for the management of patients with congestive heart failure. Myocardial failure, irrespective of the aetiology, tends to create a vicious cycle characterised by reduced cardiac output and elevated systemic vascular resistance, which further decrease cardiac output by increasing left ventricular ejection impedance. The rationale for the use of vasodilators is to interrupt the vicious cycle by decreasing the left ventricular ejection impedance by peripheral vasodilatation. Although most vasodilator agents produce qualitatively similar haemodynamic responses, quantitatively their haemodynamic effects differ considerably. Knowledge of the haemodynamic effects of the various vasodilators helps in the selection of a particular drug for the management of such patients. This article reviews the mechanisms of action, haemodynamic effects, pharmacokinetics, clinical usage and adverse effects of non-parenteral vasodilator agents currently available for the management of patients with chronic heart failure.

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.

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.

Vasodilator therapy for acute myocardial infarction and chronic congestive heart failure

Vasodilator therapy is useful adjunctive therapy in the management of both acute and chronic heart failure. Arteriolar dilators, such as hydralazine, increase cardiac output by decreasing the elevated peripheral vascular resistance that occurs in heart failure. Venodilators, such as nitrates, decrease ventricular filling pressures by redistributing blood so that more is pooled in peripheral veins. Vasodilators that produce both effects (nitro-prusside, prazosin, captopril, for example) are usually helpful in short-term improvement of hemodynamics. Long-term treatment with nonparenteral vasodilators often reduces symptoms and increases exercise tolerance, although there is inconclusive evidence regarding the effects of these agents on mortality. In acute myocardial infarction, intravenous vasodilators frequently improve cardiac performance. Evidence regarding their beneficial effects on infarct size and immediate mortality is encouraging but inconclusive. There is little evidence that they prolong life in patients who survive cardiogenic shock and leave the hospital. Thus, vasodilators can improve hemodynamics and lessen symptoms, but more evidence is needed regarding their long-term effects on survival.

Assessment of vasodilator therapy in patients with severe congestive heart failure: limitations of measurements of left ventricular ejection fraction and volumes

Although noninvasive techniques are often used to assess the effect of vasodilator therapy in patients with congestive heart failure, it is unknown whether changes in noninvasively determined left ventricular ejection fraction, volume, or dimension reliably reflect alterations in intracardiac pressure and flow. Accordingly, we compared the acute effect of sodium nitroprusside on left ventricular volume and ejection fraction (determined scintigraphically) with its effect on intracardiac pressure and forward cardiac index (determined by thermodilution) in 12 patients with severe, chronic congestive heart failure and a markedly dilated left ventricle. Nitroprusside (infused at 1.3 +/- 1.1 [mean +/- standard deviation] microgram/kg/min) caused a decrease in mean systemic arterial, mean pulmonary arterial, and mean pulmonary capillary wedge pressure as well as a concomitant increase in forward cardiac index. Simultaneously, left ventricular end-diastolic and end-systolic volume indexes decreased, but the scintigraphically determined cardiac index did not change significantly. Left ventricular ejection fraction averaged 0.19 +/- 0.05 before nitroprusside administration and increased by less than 0.05 units in response to nitroprusside in 11 of 12 patients. The only significant correlation between scintigraphically and invasively determined variables was that between the percent change in end-diastolic volume index and the percent change in pulmonary capillary wedge pressure (r = 0.68, p = 0.01). Although nitroprusside produced changes in scintigraphically determined left ventricular ejection fraction, end-systolic volume index, and cardiac index, these alterations bore no predictable relation to changes in intracardiac pressure, forward cardiac index, or vascular resistance. Furthermore, nitroprusside produced a considerably greater percent change in the invasively measured variables than in the scintigraphically determined ones.

Haemodynamic effects of dobutamine in patients with congestive heart failure receiving captopril

Treatment with captopril has proved effective in some patients with resistant heart failure. Since cardiac output responses to captopril treatment are generally small, we infused the positive inotropic agent dobutamine in six patients already receiving captopril to determine whether cardiac output could be augmented without concomitantly increasing myocardial oxygen demands. At low infusion rates of dobutamine (2.5 and 5 microgram/kg per min), a substantial rise in cardiac output was observed yet myocardial oxygen uptake remained well below baseline (pre-captopril/dobutamine) levels. At higher rates of infusion (10 and 20 microgram/kg per min) the rise in cardiac output was accompanied by a pronounced increase in myocardial oxygen uptake, and the appearance of chest pain or multifocal ventricular extrasystoles in three patients. These data indicate that captopril treatment combined with low infusion rates of dobutamine can augment cardiac output in the short term, without increasing myocardial oxygen demand.

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.

Influence of oral prazosin therapy on exercise hemodynamics in patients with severe chronic heart failure

In 10 patients with severe chronic congestive heart failure, changes in hemodynamic and cardiac performance at rest and during exercise were evaluated following short-term oral prazosin therapy. The median total dose of prazosin was 43 mg (range 23 to 95 mg) and the median duration of therapy was 47 hours (range 18 to 92 hours). Prazosin increased cardiac output and stroke volume significantly during exercise (both p less than 0.05) but not at rest (both p greater than 0.10). The magnitude of the increase in pulmonary capillary wedge pressure during exercise with the addition of prazosin was also significantly less than that during conventional therapy, suggesting improved cardiac performance during exercise. Peak oxygen consumption, peak lactate concentration and rate of disappearance of the increased concentration of lactate induced by exercise, however, remained unchanged following prazosin therapy. These findings suggest that short-term prazosin therapy, as other vasodilators, improves cardiac performance during exercise but may not necessarily influence oxygen consumption.

Long-term maintenance therapy with prazosin in congestive heart failure

We evaluated the effects of long-term maintenance therapy with oral prazosin (6-20 mg, mean 14 +/- 2 mg/d) in 14 patients with congestive heart failure. The patients were followed for 6 +/- 1 months. Eleven of the fourteen patients reported subjective improvement. Two patients required increased diuretics because of gain in body weight. Systolic blood pressure showed a slight but sustained decrease suggesting persistent vasodilator effect. Reductions in echocardiographic left ventricular end-diastolic (6.35 +/- 0.25-5.88 +/- 0.25 cm, p less than 0.05) and end-systolic (5.16 +/- 0.35-4.73 +/- 0.28 cm, p less than 0.05) diameters were observed at 2 months. However, the cardiothoracic ratio on chest x ray was unaltered. Maximum exercise tolerance time increased in eight patients (57%) during prazosin therapy. Improvement in exercise tolerance time was observed in patients with most marked clinical improvement, suggesting presence of cardiac reserve. Two patients died suddenly after reporting subjective improvement. This study shows sustained clinical improvement in most patients with heart failure treated with oral prazosin.

Ambulatory prazosin treatment of chronic congestive heart failure: development of late tolerance reversible by higher dosage and interrupted substitution therapy

To evaluate whether long-term administration of the oral vasodilator, prazosin, in the ambulatory therapy of chronic refractory congestive heart failure (CHF) results in gradual attentuation of its marked salutary peripheral circulatory relaxing actions, 16 coronary heart failure patients receiving chronic prazosin, 16 mg daily, were assessed for the development of vasodilator tolerance for 12 months. In six of these patients such tolerance was documented after 7 months which was readily surmountable, thereby allowing continuation of effective chronic prazosin therapy. Each of the six tolerance patients underwent four forearm plethysmography studies: prior to chronic prazosin (study I; 4.0 mg study dose), after 7 months prazosin (study II; 4.0 mg), repeated following 1 additional week on higher effective prazosin dose of 32 mg daily (study III; 8.4 mg), and following 2 weeks of prazosin withdrawal (study IV; 4.0 mg). The prazosin study dose increased forearm blood flow, decreased forearm vascular resistance and venous tone in studies I, III, and IV; these variables were unchanged by prazosin in study II. Despite vasodilator tolerance to the initial daily dosage at 7 months (study II), symptomatic effectiveness and improved cardiac performance were sustained throughout the entire 12 months of chronic prazosin therapy by increasing dosage (study III) and brief interruption of the vasodilator (study IV) (NYHA class IV pre-prazosin symptoms improved to class 2.7 at 3 months, class 2.4 at 6 months, and class 2.5 at 12 months chronic prazosin). This study showed that prazosin vasodilator tolerance occurred in approximately one third of CHF patients after several months of chronic prazosin therapy. More importantly, however, the present investigation demonstrated that chronic prazosin symptomatic efficacy can be maintained in such CHF patients by overcoming tolerance with higher effective prazosin dosage or brief prazosin discontinuation.

Effects of prazosin on autonomic control of circulation in essential hypertension

Prazosin, an antihypertensive agent that reduces blood pressure (BP) mainly through a blockade of alpha-adrenergic receptors, may, in theory, affect sympathetic control of circulation to an extent that impairs circulatory hemeostasis. This possibility was studied in subjects with essential hypertension by examining the cardiovascular effects of several stimuli that induce a powerful and diversified activation of the sympathetic noradrenergic activity (dynamic and isometric exercise, cold exposure) and of stimuli that exert a powerful inhibitory influence upon the sympathetic nervous system (carotid baroreceptor reflex). Before and after 15 days of continuous administration of prazosin (2-5 mg), 3 times a day, measurements were made of BP (intraarterial catheter), heart rate, cardiac output (thermodilution), and peripheral resistance. Prazosin reduced mean arterial pressure (10%) and peripheral resistance (9%) at rest, and it did not affect heart rate and cardiac output. Neurally mediated changes in arterial pressure, cardiac output, and peripheral resistance during dynamic or isometric exercise and cold exposure were unaffected by the drug; also unaffected were the cardiovascular responses to increase and decrease in carotid baroreceptor activity obtained by varying carotid transmural pressure through a variable neck pressure chamber device. Thus, the hypotensive and vasodilating effect of prazosin in essential hypertension is not accompanied by an impaired response to neural excitation influences upon the cardiovascular system. Also, the inhibitory influences originating from the carotid baroreflex are unchanged. These data indicate that circulatory homeostasis is largely preserved during administration of prazosin at clinically effective doses.

Comparison of vasodilator drug prazosin with digoxin in aortic regurgitation

Intravenous administration of the vasodilator sodium nitroprusside has beneficial haemodynamic effects in subjects with severe aortic regurgitation while acute digitalisation can produce unwanted effects associated with an increase in systemic vascular resistance. This study compares the haemodynamic effects of the vasodilator prazosin and digoxin in eight patients with isolated severe aortic regurgitation. Prazosin 5 mg orally resulted in a 12 +/- 3 (SE) per cent increase in cardiac index (thermodilution), maintained over four to six hours, while digoxin 0.75 mg intravenously did not change the cardiac index. Prazosin reduced mean arterial pressure by 9 +/- 3 mmHg and systemic vascular resistance by 18 +/- 4 per cent while digoxin resulted in a 6 +/- 2 per cent increase in the latter. Mean pulmonary capillary wedge pressure fell 3 mmHg with prazosin. In this group of patients with severe aortic regurgitation but without severe cardiac failure, the changes with either drug, studied in doses conventionally used, were small but those with prazosin were directionally more desirable than those resulting from digoxin.

Acute haemodynamic effects of oral prazosin in severe mitral regurgitation

Acute haemodynamic effects of single dose oral prazosin were studied in eight patients with mitral regurgitation. Heart rate, mean systemic arterial pressure, pulmonary arterial pressure, left ventricular filling pressure, and forward cardiac output were measured in all patients. At peak effect, prazosin reduced mean systemic arterial pressure (95 +/- 4 to 86 +/- 4 mmHg), pulmonary arterial pressure (45 +/- 6 to 23 +/- 4 mmHg), and left ventricular filling pressure (30 +/- 4 to 21 +/- 3 mmHg). Pulmonary and systemic vascular resistance also fell (316 +/- 49 to 208 +/- 43 dynes s cm-5 and 2132 +/- 148 to 1491 +/- 94 dynes s cm-5, respectively). Forward cardiac index increased from 1.89 +/- 0.12 to 2.43 +/- 0.13 l/min per m2 and stroke volume from 43 +/- 5 to 57 +/- 6 ml/beat after prazosin. The onset of these changes occurred between 15 and 30 minutes, peaked between 45 and 60 minutes, and persisted for six hours. These data indicate that in patients with mitral regurgitation oral prazosin promptly improves cardiac performance (judged by increased forward cardiac output and reduced left ventricular filling pressure) as systemic and pulmonary vascular resistance are reduced.

Platelet function studies in heart disease. VI. Enhanced platelet aggregate formation activity in congestive heart failure: inhibition by sodium nitroprusside

We studied 11 patients with congestive heart failure and 10 normal volunteers for in vivo platelet aggregate formation activity. The patients with heart failure had significantly (p less than 0.01) more circulating platelet aggregates than the normal volunteers. During sodium nitroprusside infusion, the number of circulating platelet aggregates declined to normal levels and in vitro platelet aggregation responses to epinephrine and adenosine diphosphate were also suppressed significantly (p less than 0.01). This was associated with a 30% decline in systemic vascular resistance and a 28% increase in cardiac output. In other in vitro experiments, sodium nitroprusside was found to have direct, dose-related platelet aggregation inhibitory actions. This study suggests that an increase in vascular resistance in certain heart failure patients may in part be related to an increase in circulating platelet aggregates. Direct inhibition of platelet aggregation by sodium nitroprusside may be a mechanism of its beneficial effects in heart failure.

Differences in hemodynamic effects of nitroprusside and prazosin in severe chronic congestive heart failure: evidence for a direct negative chronotropic effect of prazosin

To compare the hemodynamic effects of prazosin and nitroprusside in patients with severe congestive heart failure, nine patients with heart failure refractory to conventional therapy received oral prazosin and intravenous nitroprusside administered so as to produce a similar decrease in left ventricular filling pressure in each patient. By this comparison, both drugs produced similar decreases in mean right atrial pressure, mean pulmonary arterial pressure and systemic and pulmonary vascular resistance. However, with nitroprusside, cardiac index increased more (+0.97 versus +0.73 liters/min per m2, P less than 0.01) and mean arterial pressure decreased less (-13.7 versus -18.3 mm Hg, P less than 0.05) than with prazosin. Both drugs produced similar changes in stroke volume index (+11.7 cc/beat per m2 with nitroprusside and +12.5 with prazosin) and stroke work index (+8.1 g-m/m2 with nitroprusside and +6.6 with prazosin). Therefore, the differences in the hemodynamic responses observed with the two agents were due to the significantly greater decrease in heart rate with prazosin (-8 beats/min) than with nitroprusside (-2 beats/min, P less than 0.05). These clinical data support experimental evidence suggesting that there is a significant negative chronotropic action of prazosin independent of its peripheral vascular effects.

Non-parenteral combined afterload and preload reduction therapy in congestive heart failure

It has been shown that hydralazine is beneficial in chronic heart failure by virtue of its afterload reducing effect. Nitroglycerin paste results in venodilation and fall in left ventricular filling pressure (LVFP). Thirteen patients with chronic heart failure were given a combination of oral hydralazine and nitroglycerin paste. With oral hydralazine (75 to 100 mg every 8 h), left ventricular stroke work increased and LVFP slightly fell. Following addition of 2% nitroglycerin paste, an additional decline in mean pulmonary artery and LVFP was observed without significant changes in heart rate and arterial pressure. There were no untoward side effects from either therapy. Eight patients followed for three to eight months (mean five months) reported subjective improvement in shortness of breath and other symptoms related to ventricular dysfunction. This study shows that in certain patients with chronic heart failure, hydralazine and nitroglycerin paste combination produces salutary clinical effects on long term probably through afterload and preload reduction, respectively.