Haemodynamic and electrocardiographic effects of intravenous disopyramide (rythmodan) following acute myocardial infarction

Negative inotropic effects of disopyramide on guinea-pig papillary muscles

1. The inhibitory effects of disopyramide on electromechanical responses were investigated in guinea-pig papillary muscles driven by electrical stimuli. Disopyramide up to 10(-5) M did not cause a negative inotropic effect, while the maximum upstroke velocity of the action potential (dV/dtmax) was significantly decreased. 2. At higher concentrations, this drug dose-dependently inhibited the contraction, and dV/dtmax was further decreased. This inhibition of contraction was accompanied by a depression of the slow action potential in partially depolarized preparations by increasing [K+]0 (26 mM). 3. In preparations pretreated with nifedipine (10(-6) M) and ryanodine (10(-6) M), the contraction was almost completely inhibited. In such preparations, ouabain (2 x 10(-6) M) markedly increased the contraction, probably through the Na(+)-Ca2+ exchange mechanism. This contraction was inhibited by disopyramide above 10(-8) M, and an almost complete inhibition was caused at 3 x 10(-5) M. 4. A similar inhibitory effect was observed on the contraction increased by the lowering of [Na+]0 (36 mM). 5. These results suggest that disopyramide at high concentrations inhibits Ca influx through slow Ca2+ channels and at low concentrations, it reduces the contraction increased through the Na(+)-Ca2+ exchange mechanism. Disopyramide had a greater effect on cardiac contractility mediated by the Na(+)-Ca2+ exchange mechanism.

Disopyramide. A reappraisal of its pharmacodynamic and pharmacokinetic properties, and therapeutic use in cardiac arrhythmias

Disopyramide is a widely used class IA antiarrhythmic drug with a pharmacological profile of action similar to that of quinidine and procainamide. Over the past 10 years disopyramide has demonstrated its efficacy in ventricular and atrial arrhythmias. In therapeutic trials, usually involving small numbers of patients, the efficacy of disopyramide was comparable with that of mexiletine, perhexiline, tocainide, propafenone or prajmalium. Recent comparisons with quinidine have confirmed the similar efficacy and better tolerability of disopyramide. The suggestion from initial studies that disopyramide may be less effective than amiodarone or flecainide requires further investigation. In addition, studies have failed to demonstrate that the early administration of disopyramide after acute myocardial infarction decreases important arrhythmias or early mortality. Thus, disopyramide is now well established as an effective antiarrhythmic drug in ventricular and supraventricular arrhythmias although its role in therapy relative to that of recently introduced antiarrhythmic agents is not clear.

Hemodynamic effects of antiarrhythmic drugs

In order to use antiarrhythmic drugs safely, one must understand their hemodynamic effects. Quinidine and the calcium antagonists have direct cardiac effects and frequently opposing autonomically mediated or indirect cardiac effects. Lidocaine is exceptionally well tolerated, even by patients with severe left ventricular dysfunction. Phenytoin and procainamide have the potential for serious adverse effects, but are generally well tolerated at usual doses. Disopyramide causes serious depression of left ventricular function in many patients because of its direct myocardial depressant and peripheral vasoconstricting actions. Although bretylium causes an immediate increase in contractility, it can ultimately result in important hypotension. In this review the in vitro and in vivo hemodynamic effects of these and other antiarrhythmic drugs are discussed to provide information that will assist the clinician in using these drugs properly.

The cardiac effects of d- and l-disopyramide in normal subjects: a noninvasive study

Commercially available disopyramide is a racemic mixture of equal parts of dextrorotatory (d-) and levorotatory (l-) optical isomers. We studied the cardiac effects of i.v. administration of each isomer and the racemic mixture (dl-) in six normal males by digitized echocardiography, systolic time intervals and ECG. Both isomers and the racemic mixture produced equally marked dose-dependent negative inotropic effects (28.1 +/- 11.8% mean maximal reduction in fractional shortening of left ventricular dimension) and diastolic effects (28.6 +/- 24.1% mean maximal reduction in peak left ventricular filling rate). However, only the d-isomer prolonged QTc duration (by 13.6 +/- 5.2% at maximum, p less than 0.001 vs l-isomer). We conclude that disopyramide, in the doses used, produces marked adverse effects on left ventricle systolic and diastolic function in normal subjects independent of optical rotation. The production of these effects by the l-isomer without affecting QTc duration suggests different subcellular mechanisms for the myocardial depressant effects and some of the electrophysiologic effects of disopyramide.

The effect of saturable binding to plasma proteins on the pharmacokinetic properties of disopyramide

Disopyramide exhibits saturable binding to plasma proteins in the therapeutic plasma concentration range. Because of this property, controversy exists in the literature regarding the pharmacokinetic properties of the drug. The purposes of this study were to reassess the pharmacokinetic properties of disopyramide in humans, taking into consideration both total and unbound concentrations and to use disopyramide as a model compound to study the effect of drug binding on the renal clearance of both total and unbound drug. A single intravenous dose of disopyramide (1.5 mg/kg) was administered to eight normal volunteers. Blood and urine samples were collected for 36 h. Total concentrations of disopyramide in plasma and urine were determined by high pressure liquid chromatography. Binding of disopyramide to plasma proteins was determined by equilibrium dialysis. In all subjects the binding of disopyramide to plasma proteins was saturable, but there were considerable differences in binding between subjects. The volume of distribution, total body clearance, and renal clearances of both total and unbound drug were calculated. Because only the total body clearance and renal clearance of unbound compound are not dependent upon unbound fraction (alpha), these are the only parameters which can be reported without qualification as to the concentration. The mean +/-DS total body clearance of unbound drug in the eight subjects was 5.40 +/- 2.80 ml/min/kg. About 50% of this was due to renal elimination. A statistically significant negative correlation of the renal clearance of total disopyramide with time was observed in seven of eight subjects, whereas a significant correlation between the renal clearance of unbound disopyramide and time was observed in only one subject. This suggests that the renal clearance of unbound disopyramide is independent of alpha, while the renal clearance of total disopyramide is dependent upon alpha.

[The effect of disopyramide of left ventricular function: an echocardiographic study of the extent and time course (author's transl)]

Seven healthy volunteers were evaluated for changes in left ventricular function after a therapeutic intravenous dose of Disopyramide (2 mg/kg, maximum 150 mg given over 5 min) and, subsequently, under oral maintenance therapy (200 mg every 6 h for 3 days). Parameters of left ventricular function were determined by Echocardiography. Measurements were taken before injection, 5--25 min after intravenous Disopyramide in intervals of 5 min and 120 min after the last oral dose of the drug. Peak changes occurred 5 min after termination of injection and included increases in mean arterial pressure (10%), heart rate (22%) and endsystolic ventricular diameter (30%) and decreases in percentage (43%) and mean velocity (36%) of diameter shortening, decreases of systolic thickness and percentage of thickening of left posterior wall (27 and 43% respectively) and of interventricular septum (15 and 22% respectively) as well as a decrease of the relative thickness of left ventricular wall (40%) and of left posterior (36%) and septal (39%) amplitude. After 20 min changes in all parameters were significantly less than 5 min after injection but still significantly greater than under oral maintenance therapy. After 25 min measurements differed from those under oral Disopyramide only slightly. At both times, however, all parameters were significantly different from control values. Thus, Disopyramide given intravenously and orally in therapeutic dosage is a potent myocardial depressant in man. As the acute negative inotropic effect of intravenous Disopyramide might be of clinical importance in patients with decreased myocardial function a slow injection over 15--20 min and a dose reduction is recommended in these cases.

Hemodynamic effects of disopyramide at rest and during exercise in normal subjects

The hemodynamic effects of disopyramide phosphate, 2.0 mg/kg body weight, given intravenously over a period of five minutes were studied at rest and during exercise in ten patients without clinical or angiographic evidence of heart disease. Following disopyramide, the resting cardiac index was lower (4.0 +/- 0.6 vs 4.3 +/- 0.6 liters/min/m2, mean +/- 1 SD,P less than 0.05), while left ventricular end-diastolic pressure (16 +/- 4 vs 11 +/- 4 mm Hg, P less than 0.001), pulmonary arterial (PA) mean pressure (20 +/- 5 vs 17 +/- 5 mm Hg, P less than 0.05), and brachial arterial (BA) mean pressure (105 +/- 8 vs 96 +/- 7 mm Hg, P less than 0.05), were higher than the pre-infusion resting values. During exercise, there was no change in left ventricular end-diastolic pressure while cardiac index rose from 4.0 +/- 0.6 to 6.5 +/- 0.6 liters/min/m2 (P less than 0.001) and left ventricular stroke work index increased from 62 +/- 19 to 84 +/- 22 gm/beat/m2 (P less than 0.001). The normal hemodynamic response during exercise after disopyramide despite the apparent depression of left ventricular function at rest probably reflects the positive inotropic effect of enhanced sympathoadrenergic activity.

Disopyramide and lignocaine. A comparison of cardiac effects using echocardiography

1 The cardiac effects of disopyramide (D) and lignocaine (L) were measured and compared in normal volunteers (D n=4; L n=3) following the establishment of a series of three steady-state drug plasma concentrations spanning the therapeutic range (1.5-5 micrograms base ml-1). 2 During control and steady-state periods multiple measurements were made of heart rate, blood pressure, drug concentrations and echocardiographic measurement of cardiac dimensions and estimated left ventricular function. 3 No change in heart size or estimated function occurred with L except for a small increase in estimated cardiac output (+0.5 1 min-1) secondary to a small rise in heart rate (maximum +7 beats min-1). Blood pressure rose slightly (maximum +11 mmHg). 4 D caused an increase in heart size, marked at end systole (+0.63 cm), and a decrease in echo indices of ventricular function (25-33%). These changes were related to plasma drug concentration but were not reflected in cardiac output estimation since heart rate rose (+15 beats min-1). Blood pressure also rose (+10 mmHg). 5 Significant differences were shown between D and L at similar plasma drug concentrations. The negative inotropic effect of D may be greater than previously suggested and clinically important.

Cardiac depression by intravenous disopyramide in patients with left ventricular dysfunction

The hemodynamic effects of disopyramide phosphate were studied in nine patients with left ventricular dysfunction. After control measurements, administration of a 2 mg/kg bolus of disopyramide phosphate over 5 or 15 minutes was followed by a 20 minute 0.4 mg/kg/hour infusion and a 15 minute recovery period. Response to the 5 and 15 minute bolus injection was similar. Maximum hemodynamic effects occurred immediately after the bolus was given; there were decrements in systolic pressure (142 to 124 mm Hg)(p less than 0.005), cardiac index (2.5 to 1.8 liters/min/m2)(p less than 0.001) and stroke index (29.4 to 20.6 ml/beat/m2)(p less than 0.001), and increases in right atrial pressure (9 to 12 mm Hg)(p less than 0.005) and total peripheral resistance (21.2 to 25.7 U)(p less than 0.005). Two studies had to be terminated after the bolus was given due to profound hemodynamic deterioration. In the remainder, the systolic pressure returned to control by the end of the infusion, whereas the mean arterial pressure increasd significantly (92 to 96 mm Hg)(p less than 0.01). Little further change in mean arterial pressure, cardiac and stroke index, and total peripheral resistance occurred during the recovery period. These data indicated that intravenous disopyramide phosphate is a potent cardiac depressant when given over 5 to 15 minutes to patients with left ventricular dysfunction. It is concluded that disopyramide should not be administered to such patients unless conventional therapy fails. In such circumstances it should be used with extreme caution and careful monitoring.