Electrophysiologic and hemodynamic effects of slow-channel blocking drugs

Verapamil inhibits Kir2.3 channels by binding to the pore and interfering with PIP2 binding

The inwardly rectifying potassium current of the cardiomyocyte (IK1) is the main determinant of the resting potential. Ion channels Kir2.1, Kir2.2, and Kir2.3 form tetramers and are the molecular correlate of macroscopic IK1 current. Verapamil is an antiarrhythmic drug used to suppress atrial and ventricular arrhythmias. Its primary mechanism of action is via blocking calcium channels. In addition, it has been demonstrated to block IK1 current and the Kir2.1 subunit. Its effect on other subunits that contribute to IK1 current has not been studied to date. We therefore analyzed the effect of verapamil on the Kir channels 2.1, 2.2, and 2.3 in the Xenopus oocyte expression system. Kir2.1, Kir2.2, and Kir2.3 channels were heterologously expressed in Xenopus oocytes. Respective currents were measured with the voltage clamp technique and the effect of verapamil on the current was measured. At a concentration of 300 µM, verapamil inhibited Kir2.1 channels by 41.36% ± 2.7 of the initial current, Kir2.2 channels by 16.51 ± 3.6%, and Kir2.3 by 69.98 ± 4.2%. As a verapamil effect on kir2.3 was a previously unknown finding, we analyzed this effect further. At wash in with 300 µM verapamil, the maximal effect was seen within 20 min of the infusion. After washing out with control solution, there was only a partial current recovery. The current reduction from verapamil was the same at − 120 mV (73.2 ± 3.7%), − 40 mV (85.5 ± 6.5%), and 0 mV (61.5 ± 10.6%) implying no voltage dependency of the block. Using site directed mutations in putative binding sites, we demonstrated a decrease of effect with pore mutant E291A and absence of verapamil effect for D251A. With mutant I214L, which shows a stronger affinity for PIP2 binding, we observed a normalized current reduction to 61.9 ± 0.06% of the control current, which was significantly less pronounced compared to wild type channels. Verapamil blocks Kir2.1, Kir2.2, and Kir2.3 subunits. In Kir2.3, blockade is dependent on sites E291 and D251 and interferes with activation of the channel via PIP2. Interference with these sites and with PIP2 binding has also been described for other Kir channels blocking drugs. As Kir2.3 is preferentially expressed in atrium, a selective Kir2.3 blocking agent would constitute an interesting antiarrhythmic concept.

Pharmacological heart rate lowering in patients with a preserved ejection fraction-review of a failing concept

Epidemiological studies have demonstrated that high resting heart rates are associated with increased mortality. Clinical studies in patients with heart failure and reduced ejection fraction have shown that heart rate lowering with beta-blockers and ivabradine improves survival. It is therefore often assumed that heart rate lowering is beneficial in other patients as well. Here, we critically appraise the effects of pharmacological heart rate lowering in patients with both normal and reduced ejection fraction with an emphasis on the effects of pharmacological heart rate lowering in hypertension and heart failure. Emerging evidence from recent clinical trials and meta-analyses suggest that pharmacological heart rate lowering is not beneficial in patients with a normal or preserved ejection fraction. This has just begun to be reflected in some but not all guideline recommendations. The detrimental effects of pharmacological heart rate lowering are due to an increase in central blood pressures, higher left ventricular systolic and diastolic pressures, and increased ventricular wall stress. Therefore, we propose that heart rate lowering per se reproduces the hemodynamic effects of diastolic dysfunction and imposes an increased arterial load on the left ventricle, which combine to increase the risk of heart failure and atrial fibrillation. Pharmacologic heart rate lowering is clearly beneficial in patients with a dilated cardiomyopathy but not in patients with normal chamber dimensions and normal systolic function. These conflicting effects can be explained based on a model that considers the hemodynamic and ventricular structural effects of heart rate changes.

A second-generation computational modeling of cardiac electrophysiology: response of action potential to ionic concentration changes and metabolic inhibition

Background

Cardiac arrhythmias are becoming one of the major health care problem in the world, causing numerous serious disease conditions including stroke and sudden cardiac death. Furthermore, cardiac arrhythmias are intimately related to the signaling ability of cardiac cells, and are caused by signaling defects. Consequently, modeling the electrical activity of the heart, and the complex signaling models that subtend dangerous arrhythmias such as tachycardia and fibrillation, necessitates a quantitative model of action potential (AP) propagation. Yet, many electrophysiological models, which accurately reproduce dynamical characteristic of the action potential in cells, have been introduced. However, these models are very complex and are very time consuming computationally. Consequently, a large amount of research is consecrated to design models with less computational complexity.

Results

This paper is presenting a new model for analyzing the propagation of ionic concentrations and electrical potential in space and time. In this model, the transport of ions is governed by Nernst-Planck flux equation (NP), and the electrical interaction of the species is described by a new cable equation. These set of equations form a system of coupled partial nonlinear differential equations that is solved numerically. In the first we describe the mathematical model. To realize the numerical simulation of our model, we proceed by a finite element discretization and then we choose an appropriate resolution algorithm.

Conclusions

We give numerical simulations obtained for different input scenarios in the case of suicide substrate reaction which were compared to those obtained in literature. These input scenarios have been chosen so as to provide an intuitive understanding of dynamics of the model. By accessing time and space domains, it is shown that interpreting the electrical potential of cell membrane at steady state is incorrect. This model is general and applies to ions of any charge in space and time domains. The results obtained show a complete agreement with literature findings and also with the physical interpretation of the phenomenon. Furthermore, various numerical experiments are presented to confirm the accuracy, efficiency and stability of the proposed method. In particular, we show that the scheme is second-order accurate in space.

Management of arrhythmias in the perioperative setting

Perioperative arrhythmias are a common complication of surgery, with incidence ranging from 4% to 20% for noncardiothoracic procedures, depending on the type of surgery performed. The immediate postoperative period is a dynamic time and is associated with many conditions conducive to the development of postoperative arrhythmias. The presence of postoperative atrial fibrillation is associated with increased morbidity, ICU stay, length of hospitalization, and hospital costs. The associated burdens are expected to rise in the future, given that the population undergoing cardiac surgery is getting older and sicker. Thousands of patients undergo major surgery each year and a major complication of these procedures is the occurrence of perioperative arrhythmia. It is imperative for clinicians to be up-to-date on current management of these arrhythmias.

Effect of verapamil on long-term tachycardia-induced atrial electrical remodeling

BACKGROUND

The effect of verapamil on long-term tachycardia-induced atrial electrical remodeling has not been reported.

METHODS AND RESULTS

Forty-eight dogs were randomly divided into verapamil and control groups. The dogs in the verapamil group received verapamil 120 mg every day, those in the control group did not receive verapamil. Atrial effective refractory period (AERP), inducibility of atrial fibrillation (AF), and duration of AF were assessed before and after complete atrioventricular junction ablation with 1-day, 1-week, or 6-week rapid atrial pacing (780 bpm). AERP shortening, AERP dispersion, AERP maladaptation, and inducibility of AF after 1-day pacing was significantly attenuated by verapamil. However, verapamil did not have any significant effect on these parameters in the dogs with 1-week or 6-week pacing. Verapamil did not have any significant effect on the conduction velocity in the dogs with 1-day, 1-week, or 6-week pacing. Before rapid atrial pacing, verapamil significantly prolonged the duration of AF. In the dogs with 1-day pacing, the duration of AF measured immediately after termination of pacing was similar between the control and verapamil groups. However, in the dogs with 1-week or 6-week pacing, the duration of AF after pacing was significantly longer in the verapamil group.

CONCLUSIONS

Verapamil cannot prevent long-term (1 and 6 weeks, respectively) tachycardia-induced changes of atrial electrophysiological properties. Furthermore, verapamil increases the duration of AF in the dogs either before or after long-term rapid atrial pacing.

Felodipine or hydrochlorothiazide/triamterene for treatment of hypertension in the elderly: effects on blood pressure, hypertensive heart disease, metabolic and hormonal parameters

The aim of the study was to compare the antihypertensive efficacy of either felodipine or the diuretic combination hydrochlorothiazide/triamterene in a group (n = 65) of elderly (> or = 70 years) hypertensives (office blood pressure > or = 160/95 mmHg) with special regard to ambulatory blood pressure monitoring, hypertensive heart disease and metabolic parameters. This was a randomized, double-blind study with a treatment period of 6 months. Reduction of office and 24-hr ambulatory blood pressure was comparable with both treatment regimens; after 6 months. 18 of 29 patients in the felodipine group (62%) and 20 of 27 patients in the diuretic group (74%; p = 0.4) were controlled. While episodes of ischemic type ST-segment depression were significantly reduced in the felodipine group (from 49 to 9 episodes), there was no significant change in the diuretic group (from 24 to 21 episodes). Both regimens decreased left ventricular wall thickness, but the decline in left ventricular muscle mass index was significant only for felodipine. Felodipine did not induce any change in metabolic or hormonal parameters; the diuretic combination significantly increased serum creatinine, uric acid, plasma renin activity, and plasma prorenin. Thus, the antihypertensive efficacy of felodipine and the diuretic combination was comparable in elderly hypertensives; only felodipine, however, improved parameters of hypertensive heart disease and showed a neutral metabolic and hormonal profile.

Efficacy and tolerability of felodipine ER and diltiazem SR as monotherapy in primary hypertension: a double-blind randomized study

PURPOSE

Efficacy, tolerability, and optimal doses of felodipine ER (FER) and diltiazem SR (DSR), given as monotherapy, were evaluated in patients with mild or moderate primary hypertension.

METHODS

This was a multicenter, double-blind, parallel-group study of 98 hypertensive patients. Following a 4 weeks placebo run-in period, patients were randomized to either FER 5 mg once daily (qd) or DSR 90 mg twice daily (bid). If supine DBP was > 90 mmHg after 2 and 4 weeks treatment, the dose was increased to 10 mg FER qd or 120 mg DSR bid plus 20 mg FER qd or 180 mg DSR bid, respectively. The double-blind treatment lasted 8 weeks.

RESULTS

After 8 weeks FER treatment 70% of the patients responded (DBP < or = 90 mmHg or DBP decrease > or = 10 mmHg) and 50% became normotensive (DBP < or = 90 mmHg); the corresponding figures for DSR were 63% and 37%, respectively. No statistical significant differences in BP reduction and HR were found between the two compounds. HR did not change during the study. Seven patients discontinued due to adverse events (AEs). Five patients received FER and two patients received DSR. The AEs were similar in the two groups and generally mild.

CONCLUSIONS

At the highest dose levels of FER and DSR, no further BP reduction was observed, but there was a tendency to report more AEs. Both FER and DSR can be used as first-line therapy in hypertension.

Effects of amiodarone on the circadian rhythm and power spectral changes of heart rate and QT interval: significance for the control of sudden cardiac death

Effects of chronic amiodarone therapy on the circadian rhythmicity and power spectral changes of heart rate and QT intervals from Holter recordings were evaluated in three groups of patients: group 1 baseline (n = 10); group 2, treated for 3 to 6 months (n = 11); and group 3, treated for > 1 year (n = 13). Amiodarone reduced heart rate, which reached steady state at 3 to 6 months; bradycardia was evident during the entire 24 hours. The corrected QT (QTc) interval increased as a function of treatment duration. It was 457 +/- 39, 530 +/- 28 (p < 0.001), and 581 +/- 36 (p < 0.0002) msec for groups 1, 2, and 3, after 6 months, respectively. The circadian rhythmicity of QTc was abolished in group 3. Power spectral analysis showed a tendency for amiodarone to reduce both R-R and QT interval variabilities, suggesting inhibition of autonomic control on the heart by the drug. The effectiveness of amiodarone against ventricular arrhythmias may result in part from the sustained bradycardia in concert with continuous uniform prolongation of myocardial repolarization.

Bepridil treatment of chronic stable angina: a review of comparative studies versus placebo, nifedipine, and diltiazem

The antianginal efficacy of bepridil, a calcium antagonist with an extended plasma elimination half-life, has been compared with placebo and the calcium antagonists nifedipine and diltiazem in patients refractory to diltiazem. The earliest observations in the United States of antianginal effects of bepridil were revealed in a single-blind, multicenter, placebo-controlled trial of 77 patients with chronic stable angina pectoris that demonstrated that bepridil (300 mg/day) improved exercise duration by 26%, from 6.9 +/- 0.4 (standard error of the mean) to 8.7 +/- 0.5 minutes (p less than 0.001), and exercise work by 52%, from 2.7 +/- 0.3 to 4.1 +/- 0.4 x 10(-3) KPM (p less than 0.001), on a standardized treadmill protocol, and it reduced angina frequency by 68%, from 8.5 +/- 1.1 to 2.7 +/- 0.7 attacks per week, and nitroglycerin use by 76% (p less than 0.001). Minor side effects such as nausea, epigastric discomfort, and tremor were infrequent and no major side effects occurred. Double-blind, parallel-design treatment evaluations confirmed beneficial effects of bepridil alone and in combination with beta blockade. Chronic efficacy was confirmed by evaluations up to 24 months in a controlled withdrawal study. Antianginal effects of nifedipine were compared with those of bepridil in a double-blind, parallel group study of 101 patients with chronic stable angina treated for 3 months. Bepridil (mean final dose 284 mg/day; range 200-400 mg/day) produced modest but statistically significantly (p less than 0.05) greater improvements in exercise work, time to angina, or 1 mm ST-segment change than nifedipine (mean final dose 59 mg/day; range 30-120 mg/day).(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative efficacy and safety of bepridil and diltiazem in chronic stable angina pectoris refractory to diltiazem. The Bepridil Collaborative Study Group

The efficacy and safety of bepridil hydrochloride (200 to 400 mg/day) were evaluated in patients with chronic stable angina refractory to maximal tolerated doses of diltiazem (median 360 mg/day) in a randomized, multicenter, double-blind, parallel study. Baseline diltiazem data were obtained during a 2-week period, after which 86 patients were randomized to bepridil (n = 46) or diltiazem (n = 40). Angina frequency, nitroglycerin consumption and ischemic manifestations induced by exercise treadmill testing were evaluated over 8 weeks. Bepridil significantly (p less than 0.05) increased time to angina onset, time to 1 and 2 mm of ST-segment depression, total exercise time and total work over baseline values. Changes in time to angina onset and time to 1 mm of ST-segment depression were significantly (p less than 0.05) greater for bepridil than for diltiazem. Angina frequency and nitroglycerin consumption did not differ significantly between groups. Compared with baseline, bepridil significantly (p less than 0.001) decreased heart rate (mean 4 beats/min) and prolonged QTc (mean 35 ms). The most frequent adverse effects in both groups were nausea, asthenia, dizziness, headache and diarrhea. Four patients taking bepridil and 1 taking diltiazem withdrew from the study because of adverse reactions. No sudden deaths, myocardial infarctions or instances of sustained ventricular tachycardia or torsades de pointes occurred in either group. The data indicate that bepridil provided safe and effective antianginal and antiischemic therapy in patients with chronic stable angina who exhibited less than optimal response to maximal tolerated doses of diltiazem.

Combined negative inotropic effects of calcium entry blockers and isoflurane on canine isolated heart muscles

The combined negative inotropic effects of isoflurane and calcium entry blockers (verapamil, diltiazem, nifedipine, nicardipine) were studied utilizing isolated heart preparations of ventricular muscles from dogs. All of these calcium entry blockers exerted dose-dependent decreases in maximal velocity of shortening (Vmax), maximal developed isometric force (Fm), and the maximal first derivative of Fm (maximal dF/dt). Dose-dependent decreases of these variables of muscle mechanics were augmented in isoflurane-depressed myocardium. At equimolar concentrations, direct myocardial depression was demonstrated in the following order of severity: nifedipine > diltiazem = verapamil > nicardipine. Percent depressions of Vmax, Fm and maximal dF/dt were significantly greater in muscles when calcium entry blockers were combined with 1MAC isoflurane than in muscles of calcium entry blockers alone. These data suggest that the negative inotropic effects of verapamil, diltiazem, nifedipine, and nicardipine were potentiated by isoflurane.

Electrophysiologic effects of bepridil in patients with refractory ventricular tachycardia assessed by programmed electrical stimulation

The effect of intravenous bepridil, a new calcium antagonist with class I and III properties, was tested in 21 patients with sustained ventricular tachyarrhythmias refractory to a mean of five antiarrhythmic agents as assessed by programmed right ventricular stimulation. At control electrophysiologic study without antiarrhythmic agents, sustained monomorphic ventricular tachycardia (VT) was initiated in 20 patients and ventricular fibrillation (VF) was initiated in one patient. After 3 mg/kg of bepridil was administered, VT was still inducible in 19 patients (3 patients had self-terminating VT); the other 2 patients had no inducible VT after bepridil. Bepridil prolonged significantly the QTc interval, the effective refractory period, and the cycle length of induced ventricular tachycardia. Two patients with no inducible VT after intravenous bepridil were placed on oral bepridil (300 mg/day). One patient died suddenly and one patient died of progressive heart failure. The results seem to indicate that the efficacy of bepridil in patients with refractory ventricular tachycardia is limited.

Short-term control of supraventricular tachycardia with verapamil infusion and calcium pretreatment

Nineteen consecutive patients with atrial fibrillation/flutter or other types of supraventricular tachycardia were given intravenous (IV) calcium salts (1 g) followed by verapamil infusion at a rate of 1 mg/min. Successful treatment was defined as control of ventricular response to less than or equal to 100 beats per minute (bpm) or conversion to sinus mechanism in patients with atrial arrhythmias: 11 patients had atrial fibrillation; three had atrial flutter; four had reentrant supraventricular tachycardias (SVT); and one had paroxysmal SVT. Therapy was successful in all patients. The mean dose of verapamil required to achieve desired outcome was 20 mg. Heart rate showed no significant change as a result of calcium pretreatment (160 bpm v 151 bpm). However, heart rate was significantly decreased, to 95 bpm, after treatment with verapamil. Blood pressure showed no change from baseline with either calcium or verapamil therapy. Verapamil infusion following IV calcium successfully treats atrial fibrillation/flutter or SVTs without depressing systemic blood pressure.

The effect of propranolol, verapamil and dantrolene treatment on cardiac hypertrophy, enhanced myocardial contractility and tachycardia in the hyperthyroid rat

Experimentally induced hyperthyroidism is associated with cardiac hypertrophy, tachycardia and elevated myocardial contractility. To investigate the possibility of ameliorating the cardiac changes pharmacologically, hyperthyroid rats were treated with propranolol, verapamil or dantrolene. Cardiac hypertrophy was assessed from the heart mass: body mass ratio and cardiac function was measured in vitro. Both verapamil and propranolol reversed the cardiac hypertrophy of the hyperthyroid animals from 0.92 +/- 0.02 mg.g-1 to 0.70 +/- 0.01 mg.g-1 (P less than 0.001) and 0.72 +/- 0.02 mg.g-1 (P less than 0.001) respectively. Verapamil was effective in reducing the spontaneous heart rate from 331 +/- 8 beats.min-1 to 273 +/- 7 beats.min-1 (P less than 0.001) while propranolol reduced the dP/dtmax of the hyperthyroid hearts from 4089 +/- 87 mmHg.s-1 to 3497 +/- 97 mmHg.s-1 (P less than 0.001). Dantrolene had no effect on any parameter. We conclude from our results that cardiac hypertrophy of the hyperthyroid heart can be reversed by treatment with propranolol and verapamil probably via their inotropic and chronotropic properties.

Clinical pharmacology, pharmacokinetics, and hemodynamic effects of nicardipine

The dihydropyridine derivatives constitute a distinct subcategory of calcium channel blockers that have marked peripheral vascular effects with minimal or no electrophysiologic actions when administered to intact animals or humans. These dihydropyridine derivatives are structurally similar to nifedipine, the most widely studied dihydropyridine. The derivatives have varying affinities for different regional circulations, and there may be an important relationship between structure and activity of these compounds with respect to the predilection of the site of their action in vascular tissue. It is possible that such differences may be of clinical significance. As a class, the dihydropyridines exert reasonably distinct hemodynamic changes that may be of particular importance in the treatment of hypertension, cardiac failure, and regurgitant valvular lesions. Nicardipine hydrochloride is a newer agent that has undergone extensive evaluation in recent years. Pharmacologically and electrophysiologically, it resembles other dihydropyridines. Unlike nifedipine, however, it can be administered by both the intravenous and oral routes. There are additional differences between its properties and those of other calcium channel blockers. For example, nicardipine appears to produce a greater increase in coronary sinus blood flow than other calcium channel blockers. The clinical significance of this finding is unclear. In addition, nicardipine appears to increase myocardial contractility, even in patients with severe congestive cardiac failure. Nicardipine produces a dose-dependent decrease in blood pressure and systemic vascular resistance with increases in heart rate, left ventricular dP/dt, LV ejection fraction, cardiac output, and stroke work index, but no significant change in LV end-diastolic pressure. Clearly, the drug has negligible venodilator actions.(ABSTRACT TRUNCATED AT 250 WORDS)

Digoxin or verapamil or metoprolol for heart rate control in patients with mitral stenosis--a randomised cross-over study

The effect and choice of a drug to control heart rate for symptomatic improvement in patients with isolated mitral stenosis with normal sinus rhythm (n = 10) or atrial fibrillation (n = 10) were studied. Digoxin (0.25-0.5 mg daily), metoprolol (50-100 mg twice a day) and verapamil (40-80 mg three times a day) were evaluated for this purpose. An open randomised cross-over design was followed. The efficacy of a drug was evaluated by: (1) subjective improvement on a visual analog scale, and (2) objective improvement on repeated multi-stage symptom-limited treadmill exercise. In patients with sinus rhythm greater than or equal to 50% subjective improvement was seen in 90%, 40% and nil with metoprolol, verapamil and digoxin, respectively. The total work done by these patients was 1008 +/- 541 kpm (control), 2869 +/- 1418 kpm on metoprolol, 2369 +/- 884 kpm on verapamil and 1654 +/- 918 kpm on digoxin. In patients with atrial fibrillation greater than or equal to 50% subjective improvement was seen in 80%, 40% and 30% with verapamil, metoprolol and digoxin, respectively. The total work done by these patients was 555 +/- 232 kpm (control), 1379 +/- 553 kpm on verapamil, 1251 +/- 575 kpm on metoprolol and 716 +/- 340 kpm on digoxin. The degree of improvement on a drug appeared to be a function of its ability to control resting and exercise heart rates in two different rhythms in these patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophysiological effects of bepridil and its quaternary derivative CERM 11888 in closed chest anaesthetized dogs: a comparison with verapamil and diltiazem

1. The electrophysiological effects of bepridil, its quaternary derivative, CERM 11888 (methylpyrrolidinium bromide) (both 2.5 mg kg-1 i.v.) and those of verapamil and diltiazem (0.2 mg kg-1 i.v.) were studied in closed chest anaesthetized dogs at doses used in clinical studies. 2. The four drugs caused a bradycardia with the following order of potency: bepridil greater than CERM 11888 greater than diltiazem greater than verapamil. 3. All the compounds slowed conduction in the AV node, increased the refractory period (RP) and decreased Wenckebach rates with the following order: verapamil much greater than diltiazem greater than bepridil greater than CERM 11888. 4. Verapamil and diltiazem did not affect conduction or the RP in atria while bepridil weakly slowed the former and markedly increased the latter. CERM 11888 caused a lengthening of RP but this was a delayed effect. 5. In the ventricle, bepridil and CERM 11888 caused a small increase in the QRS and a more pronounced increase in the RP. Both compounds increased QTc but did not modify HV. Verapamil and diltiazem had no significant effects at the ventricular level. 6. Our results confirm that the main sites of action of calcium antagonists are the SA and AV nodes. Bepridil has a broader spectrum of activity and also acts at the atrial and ventricular levels. A comparison of the effects of bepridil with those of its quaternary derivative suggests the involvement of an intracellular action in the electrophysiological effects of bepridil.

Calcium channel antagonism and beta blockade in combination--a therapeutic alternative in cardiovascular disorders. A review

Calcium-channel antagonists and beta-adrenergic blocking agents have become important modalities in the cardiovascular therapeutic armamentarium. These drugs are often administered as monotherapy to a wide range of cardiological patients with angina pectoris, hypertension, arrhythmias, congestive heart failure, and other diseases. Since within each class these drugs exhibit pharmacologic differences, it follows that their effectiveness varies in different disease states and that they exhibit a wide variety of side effects. In an attempt to optimize therapy, the individual drugs from these two classes can be combined; and the efficaciousness and side-effect profile of various combinations between calcium-channel antagonists and beta blockers are discussed in this review. Recommendations as to which patients may benefit from a combination and as to which patients may be harmed by the combination therapy will be made. Very few studies have compared the safety and efficacy of a single agent with the combination and with placebo in a controlled randomized fashion. To determine which therapy is superior and to determine which combination one should recommend under what circumstances, such placebo-controlled, randomized trials are a necessity, and will hopefully be performed although the complexity is enormous.

Calcium antagonists and heart failure

The systemic vasodilatory actions of the calcium antagonists make them potentially attractive for use as afterload reducing agents in patients with left ventricular failure. However, unlike other vasodilator drugs, these drugs also exert a direct negative inotropic effect on the myocardium. Clinical data suggest a limited role for the calcium antagonists as vasodilator therapy in patients with heart failure.

Effect of calcium channel blockers on hemodynamic responses to defibrillation

The hemodynamic response to sequences of ventricular fibrillation and defibrillation includes an adrenergic component that is important for the maintenance of blood pressure after successful defibrillation. Because calcium channel blocking drugs have antiadrenergic effects, we hypothesized that they might blunt the adrenergic response to defibrillation. Ventricular fibrillation was induced in 35 closed-chest dogs. Each received 4 to 7 direct current transthoracic shocks at three energy levels to determine defibrillation energy requirements. Heart rate and blood pressure were recorded. Energy sequences were repeated after 45 minutes of no intervention (control, n = 5) or after 45-minute infusions of diltiazem (0.1 mg/kg/min, n = 10), verapamil (0.1 mg/kg bolus plus 0.01 mg/kg/min, n = 10), or nifedipine (40 micrograms/min for 3 minutes plus 2 to 20 micrograms/min adjusted to maintain a 10 mm Hg drop in mean arterial pressure, n = 10). Our results show that the normal post-shock rise in mean arterial pressure was blunted by the calcium channel blockers diltiazem (systolic arterial pressure at 15 and 60 seconds post-shock, pre-drug versus post-drug: 102 +/- 9 versus 64 +/- 9 mm Hg and 113 +/- 10 versus 87 +/- 6 mm Hg; p less than 0.05) and verapamil (108 +/- 9 versus 78 +/- 12 mm Hg and 113 +/- 7 versus 90 +/- 10 mm Hg, p less than 0.05). There were no differences in blood pressure responses after nifedipine treatment or no drug. Heart rate responses were not altered by diltiazem or verapamil; after nifedipine administration, post-shock heart rates were slower.(ABSTRACT TRUNCATED AT 250 WORDS)

Hemodynamic and endocrine effects of acute and chronic administration of nifedipine

Although it is well known that calcium channel blockers can influence contraction of vascular smooth muscle, there is less knowledge on its effect on excitation contraction coupling in the endocrine glands and more specifically on insulin and glucagon release. In this study, nifedipine was administered in doses of 40 to 80 mg/day to 14 patients with essential hypertension, and its hemodynamic effects were evaluated by non-invasive methods, and its effect on glucose metabolism by an arginine infusion test. Nifedipine produced a significant reduction in systolic and diastolic blood pressure, both after the first dose (30/12 mm Hg) and after 8 weeks of administration (19/12 mm Hg). There were no significant changes in cardiac output (5.1 to 4.9 L/min), muscle (2.4 to 3.2 mL/sec/min) or cutaneous basal flow (9.8 to 8.6 mL/100 mL) as measured non-invasively by echocardiogram and by plethysmography. Insulin and glucagon release were evaluated by the arginine infusion test. Nifedipine produced a tendency towards an increase in glucagon release and a reduction in insulin release although these changes did not reach statistical significance. In this group of patients, nifedipine produced a significant reduction in systolic and diastolic pressure, but no significant changes in insulin or glucagon plasma levels.

Hemodynamic and endocrine effects of acute and chronic administration of nifedipine

Although it is well known that calcium channel blockers can influence contraction of vascular smooth muscle, there is less knowledge on its effect on excitation contraction coupling in the endocrine glands and more specifically on insulin and glucagon release. In this study, nifedipine was administered in doses of 40 to 80 mg/day to 14 patients with essential hypertension, and its hemodynamic effects were evaluated by non-invasive methods, and its effect on glucose metabolism by an arginine infusion test. Nifedipine produced a significant reduction in systolic and diastolic blood pressure, both after the first dose (30/12 mm Hg) and after 8 weeks of administration (19/12 mm Hg). There were no significant changes in cardiac output (5.1 to 4.9 L/min), muscle (2.4 to 3.2 mL/sec/min) or cutaneous basal flow (9.8 to 8.6 mL/100 mL) as measured non-invasively by echocardiogram and by plethysmography. Insulin and glucagon release were evaluated by the arginine infusion test. Nifedipine produced a tendency toward an increase in glucagon release and a reduction in insulin release although these changes did not reach statistical significance. In this group of patients, nifedipine produced a significant reduction in systolic and diastolic pressure, but no significant changes in insulin or glucagon plasma levels.

Effects of vasodilators on the coronary circulation in congestive heart failure

Pressure or volume overload of the myocardium increases the wall stress, particularly of the subendocardium, and leads to hypertrophy. Even though cardiac hypertrophy is viewed as a beneficial compensatory process that normalizes wall stress, the increased muscle mass carries with it the need of increased blood supply. Overall flow per unit mass is similar at rest in hypertrophic and normal hearts but a reduction of flow to the subendocardium and an increase in minimal coronary vascular resistance have been described. Thus, the potential exists for a vasodilator-induced steal mechanism shunting blood away from potentially ischemic areas. Angiotensin-converting enzyme inhibitors reduced myocardial oxygen consumption and coronary blood flow in parallel manner in some studies, indicating preserved coronary autoregulation, but there is also some evidence of a coronary vasodilator effect. Calcium antagonists reduce coronary vascular resistance and improve the myocardial demand-supply ratio, but the clinical usefulness of the newer compounds with supposedly little or no negative inotropic effects remains to be established. Hydralazine improved the myocardial oxygen demand-supply ratio in patients with dilated cardiomyopathy, but metabolic function may deteriorate more often after hydralazine than after angiotensin-converting enzyme inhibitors in patients with coronary heart disease. Similar observations have been made using alpha-adrenergic blockers. Although progress has been made in the understanding of the coronary circulation and the influence of vasodilators in congestive heart failure, many questions await clarification using refined or new methodology.

Calcium channel blockers

The calcium channel blockers initially were approved for the treatment of classical and variant angina pectoris. Recent studies indicate that these agents also are useful in such diverse conditions as pulmonary and systemic hypertension, hypertrophic cardiomyopathy, arrhythmias, asthma, Raynaud's syndrome, esophageal spasm, myometrial hyperactivity, cerebral arterial spasm, and migraine.

Effects on hemodynamics and left ventricular ejection fraction of intravenous bepridil for impaired left ventricular function secondary to coronary artery disease

To define the hemodynamic effects of bepridil in patients with depressed left ventricular (LV) function, 22 patients with an LV ejection fraction (EF) of 0.45 or less were studied before and after 2 mg/kg (n = 11) and 4 mg/kg (n = 11) of intravenous bepridil. Maximal hemodynamic effects were evident between 15 and 30 minutes after drug infusion. After 2 mg/kg, heart rate decreased 9% (p less than 0.01), cardiac index 17% (p less than 0.01), LV dP/dt max 16% (p less than 0.01), stroke work index 14% (p less than 0.01) and mean aortic pressure 8% (difference not significant). Right atrial pressure increased 8% (not significant), pulmonary arterial wedge pressure 24% (p less than 0.01) and systemic vascular resistance 17% (p less than 0.01). After administering 4 mg/kg of bepridil the changes in heart rate, cardiac index, right atrial pressure, LV dP/dt max, mean aortic pressure and systemic vascular resistance were almost identical to those after the smaller dose. The larger dose produced a 40% (p less than 0.01) increase in pulmonary arterial wedge pressure and a 22% decrease in stroke work index (p less than 0.01), but only the change in wedge pressure was significantly greater (p less than 0.01) than that produced by the lower dose. Radionuclide-determined LVEF decreased 6% (p less than 0.05), from 0.33 +/- 0.14 after 2 mg/kg and 11% (p less than 0.05) from 0.27 +/- 0.11 after 4 mg/kg of bepridil. The data indicate that bepridil exerts significant negative inotropic and chronotropic effects in patients with impaired LV function.

Electrical activity in the heart during hyperkalemic hypothermic cardioplegic arrest: site of origin and relationship to specialized conduction tissue

Previous studies from this laboratory have shown that low-amplitude electrical activity (LEA) may occur during standard hyperkalemic hypothermic cardioplegic arrest and be undetected by routine monitoring techniques. The present study was designed to elucidate the electrophysiological nature of LEA. Ten dogs were monitored continuously during standard cardioplegic arrest using a 32-channel data acquisition system. In 7 animals (Part I), electrophysiological mapping of the lower right atrial septum during arrest was performed. The initial site of activation of LEA was consistently recorded from the region of the lower atrial septum prior to atrial or ventricular electrical activation. The site of origin of LEA was thus localized to the anatomical region of the atrial septum containing the atrioventricular nodal conduction tissue. In Part II, the electrophysiological mechanism of LEA was investigated in the remaining 3 animals utilizing an intrinsic property of specialized conduction tissue. Inclusion of a calcium channel-blocking agent in standard cardioplegic solution completely prevented the development of LEA in all 3 animals, which is in contrast to findings in previous studies using standard cardioplegic solution alone. These data suggest that LEA may be related to calcium-mediated activation of specialized conduction tissue. This mechanism of activation may explain why LEA cannot be detected by the intraoperative monitoring techniques routinely employed.

Cardiac dysrhythmias in the acute setting: recognition and treatment or anyone can treat cardiac dysrhythmias

The two primary goals in dysrhythmia therapy are: to control the ventricular rate (between 70 and 100 beats per minute) and to maintain sinus rhythm. Maintenance of sinus rhythm is definitely secondary. If a patient is hemodynamically unstable, but has a ventricular rate between 60 and 100 beats per minute, the trouble is almost certainly not due to the cardiac rhythm. Normal conduction velocity is fast. An impulse is transmitted by healthy Purkinje fibers at 2 to 3 meters per second. This means that the entire ventricle, when activated by the Purkinje system, is activated in 80 milliseconds. When a superventricular impulse is transmitted to the ventricles via the A-V node, the ventricle should be activated (depolarized) in less than 80 milliseconds. Conversely, if an impulse is generated at an ectopic ventricular site, it does not access the high velocity Purkinje system as rapidly. A ventricular origin beat (PVC) thus, takes longer to activate the entire ventricle. The QRS is, therefore, longer (or wider). A wide QRS signifies aberrant ventricular conduction. When a dysrhythmia originates above the A-V node, the therapy is pharmacologic A-V nodal blockade (verapamil). When a dysrhythmia originates below the A-V node, therapy is pharmacologic (Lidocaine) or electrical (cardioversion). If uncertain or a patient is unstable, cardioversion is always acceptable. Thus; with an unstable patient, proceed immediately to cardioversion; with a narrow complex tachycardia (superventricular) proceed to verapamil; and with a wide complex (ventricular) tachycardia give Lidocaine and proceed to cardioversion.

Electrophysiologic effects and long-term efficacy of bepridil for recurrent supraventricular tachycardias

Thirteen patients underwent electrophysiologic evaluation for recurrent supraventricular tachycardia (SVT). The effects of intravenous bepridil (4 mg/kg) were evaluated during the initial study in 5 patients, and 12 patients underwent repeat study 7 to 10 days later taking oral bepridil, 300 to 400 mg/day. Intravenous bepridil increased the pacing cycle length inducing atrioventricular (AV) (276 +/- 43 vs 334 +/- 31 ms, p less than 0.01) and ventriculoatrial (VA) block (268 +/- 34 vs 310 +/- 35 ms, p less than 0.001), the retrograde refractory period of the accessory pathway (251 +/- 17 vs 295 +/- 25 ms, p less than 0.05) and the ventricular refractory period (216 +/- 17 vs 226 +/- 11 ms, p less than 0.05), and prevented induction of sustained SVT in 3 patients. Oral bepridil increased the sinus cycle length (723 +/- 64 vs 800 +/- 118 ms, p less than 0.05), corrected QT (403 +/- 14 vs 431 +/- 21 ms, p less than 0.05) and the pacing cycle inducing AV (288 +/- 63 vs 353 +/- 78 ms, p less than 0.01) and VA block (271 +/- 31 vs 408 +/- 124 ms, p less than 0.01). It prolonged the refractory period of the atrium (195 +/- 29 vs 233 +/- 36 ms, p less than 0.05), AV node (264 +/- 35 vs 303 +/- 22 ms, p less than 0.05), ventricle (221 +/- 16 vs 245 +/- 21 ms, p less than 0.01), accessory pathway in the AV (290 +/- 47 vs 329 +/- 54 ms, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Hemodynamic and electrocardiographic correlates of symptomatic and silent myocardial ischemia: pathophysiologic and therapeutic implications

Numerous hemodynamic, electrocardiographic, metabolic and radionuclide measurements in various subsets of patients with coronary artery disease (CAD) reveal that ischemia does not always occur on the basis of increases in myocardial oxygen consumption. Continuous hemodynamic monitoring indicates that most episodes of myocardial ischemia are not preceded by increases in such major determinants of oxygen consumption as heart rate or blood pressure, but that these usually increase in response to the development of ischemia. The development of pain during ischemia is a late feature and most episodes are silent. There are no significant differences in the hemodynamic characteristics of symptomatic versus asymptomatic episodes of myocardial ischemia in patients with angina at rest or between those associated with ST-segment depression and those with ST-segment elevation. Continuous Holter recordings analyzed by compact analog technique in hospitalized and ambulatory patients with ischemic heart disease indicate that in both unstable and chronic stable angina, over two-thirds of myocardial ischemic episodes are clinically silent. Symptomatic and silent episodes do not differ significantly with respect to duration. Most symptomatic and asymptomatic episodes are not triggered by increases in the determinants of oxygen demand. Such episodes may arise on the basis of a critical reduction in the lumen of the diseased coronary artery leading to a primary reduction in blood flow. Intermittent obstruction due to changes in coronary vasomobility or possibly formation of thrombi may be a common mechanism for the pathogenesis of myocardial ischemia in patients with a varying spectrum of coronary artery lesions. At present, the precise clinical and prognostic significance of silent ischemia in CAD is not completely defined.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium antagonists and beta blockers in the control of mild to moderate systemic hypertension, with particular reference to verapamil and propranolol

The antianginal and antiarrhythmic role of calcium antagonists is well established. Recent preliminary studies have indicated that, like beta blockers, calcium antagonists may produce short- and long-term hypotensive effects in patients with mild to moderate essential hypertension. The pharmacologic properties of calcium antagonists provide a clear rationale for their use in the control of essential hypertension. The comparative hypotensive effects of verapamil (80 to 160 mg 3 times a day) and propranolol (40 to 120 mg 3 times a day) were evaluated over 4 weeks, preceded by a 4-week placebo phase, in a double-blind protocol in 17 patients with mild to moderate hypertension. Verapamil (n = 10) reduced the mean sitting systolic blood pressure by 10.7% (p less than 0.01) and standing by 7.6% (p less than 0.04). The corresponding data for propranolol (n = 7) were 4.8% (not significant) and 5% (p = 0.04). Verapamil reduced the sitting diastolic blood pressure by 10.8% (p less than 0.01), propranolol by 7.5% (p = 0.01); the standing diastolic blood pressure was reduced by 10.7% with verapamil (p less than 0.01) and by 8.6% (p = 0.01) with propranolol. With verapamil the mean heart rate fell from 77.60 +/- 8.42 to 70.20 +/- 4.85 beats/min (p = 0.03); with propranolol it fell from 76.85 +/- 6.91 to 66.29 +/- 4.54 beats/min (p less than 0.01). Although a trend towards a slightly greater hypotensive effect was apparent with verapamil compared with propranolol, the difference was not statistically significant. It is concluded that verapamil and propranolol exert comparable hypotensive potency in patients with mild to moderate hypertension.

Calcium-channel blockers for combined angina pectoris and systemic hypertension

Calcium-channel blockers have been successfully used in the treatment of angina of effort and systemic hypertension. Many patients present with concomitant angina pectoris and hypertension. Controlled clinical trials demonstrate that the calcium-channel blockers are safe and effective as monotherapy in the treatment of these patients, and that their use compares favorably with that of propranolol. The effectiveness of these agents in hypertension appears to be primarily due to their ability to induce systemic vasodilation. Calcium-channel blockers have several therapeutic effects in angina pectoris. Beneficial actions on the major determinants of oxygen consumption, i.e. heart rate, blood pressure and contractility, are generally seen. The potent coronary vasodilating actions of these agents allow for increased coronary blood flow. Improvements in ventricular compliance, regression of left ventricular hypertrophy and cardioprotection appear to be additional effects of the calcium-channel blockers; their contribution to the drugs' overall therapeutic efficacy is presently being evaluated. Calcium-channel blockers are a welcome addition to drug regimens available for the management of patients with coexisting angina pectoris and hypertension.

The mechanism of action of calcium antagonists relative to their clinical applications

As a class of therapeutic agents calcium antagonists have attracted increasing attention in recent years. Their major indications have been in the treatment of ischaemic myocardial syndromes, certain cardiac arrhythmias, hypertension, obstructive cardiomyopathies, and a number of lesser clinical disorders in which their role is less clearly defined. With the widening spectrum of therapeutic utility and an increasing plethora of newer agents under development, it is of importance to relate the overall pharmacodynamics of individual agents to their clinical effects. Calcium antagonists have a variable specificity for cardiac and peripheral activity. Based on such activity, it is useful to construct a classification of these compounds, new and old, into four categories. Type I agents, typified by verapamil and its congeners (tiapamil and gallopamil) and diltiazem, prolong AV nodal conduction and refractoriness with little effect on ventricular or atrial refractory period. These actions account for their direct antiarrhythmic properties. Type II agents include nifedipine and other dihydropyridines. In vivo, these agents are devoid of electrophysiologic effects in usual doses. They are potent peripheral vasodilators with some selectivity of action for different vascular beds; their overall haemodynamic effects are dominated by this peripheral vasodilatation and reflex augmentation of sympathetic reflexes. Type III agents include flunarizine and cinnarizine (piperazine derivatives), which, in vitro and in vivo, are potent dilators of peripheral vessels, with no corresponding calcium-blocking actions in the heart. Type IV agents are agents with a broader pharmacologic profile (perhexiline, lidoflazine and bepridil); they block calcium fluxes in the heart, in the peripheral vessels, or both. They may inhibit the fast channel in the heart and have other electrophysiologic actions. A clear understanding of the varied pharmacologic properties of the different classes of calcium antagonists is likely to provide a rational basis for the use of these agents in clinical therapeutics.

Antiarrhythmic drugs: electrophysiological basis of their clinical usage

Cardiac arrhythmias arise from abnormalities of impulse initiation or impulse conduction or both. A review of the electrophysiological mechanisms of the genesis of cardiac arrhythmias and of the electrophysiological principles of the treatment of the cardiac arrhythmias leads to: categorization of antiarrhythmic drugs into five classes based on their dominant cardiac electrophysiological actions; a series of categories of their effects on impulse initiation and impulse conduction in different types of cardiac cells; and a systematic approach to pharmacological management of cardiac arrhythmias.

Mechanism of acute hypercalcemic hypertension in the conscious rat

Acute hypercalcemia in the conscious, unanesthetized rat, achieved by a 30-minute infusion of CaCl2 (serum calcium level, 12.8 +/- 0.6 mg/dl) resulted in significant elevation of mean arterial pressure (from 112 +/- 2 mm Hg to 129 +/- 3 mm Hg, p less than 0.001). This pressor response was associated with a significant increase in systemic vascular resistance, from 0.45 +/- 0.02 mm Hg/(ml/min)/kg body weight to 0.50 +/- 0.02 mm Hg/(ml/min)/kg body weight (p less than 0.05), but it caused no alteration in cardiac index. The pressor response to acute hypercalcemia does not appear to be mediated by vasopressor hormones or attenuated by vasodepressor hormones since inhibition of the renin-angiotensin system (nephrectomy), catecholamines (central and peripheral 6-hydroxydopamine), vasopressin (vascular antagonist), prostaglandins (indomethacin), and parathyroid hormone (parathyroidectomy) did not significantly alter the pressor response to infusion of CaCl2 in spite of similar serum calcium levels in all groups of animals. Rather, the pressor response to acute hypercalcemia seems to be mediated by a direct action of calcium ion on smooth muscle and perhaps myocardial cell contractility, since pretreatment with the calcium channel blockers verapamil or nifedipine blocked the pressor response to acute hypercalcemia.

Potentiation by nifedipine and diltiazem of the hypotensive response after contrast angiography

Arterial hypotension has been demonstrated after left ventriculography using currently available ionic contrast agents. This adverse hemodynamic response is significantly decreased with the newer nonionic contrast agents. Calcium channel antagonists also produce a hypotensive response. The potentially accentuated hypotensive response after bolus contrast angiography in patients receiving the calcium antagonists nifedipine and diltiazem was evaluated. Three contrast agents were compared: two ionic agents (Renografin-76 and Hypaque-76) and a nonionic agent (iopamidol). The hemodynamic response after left ventriculography was assessed in 125 patients, 65 receiving nifedipine or diltiazem and 60 not receiving these drugs. Baseline clinical characteristics were similar in all patient groups. The hypotensive response was significantly greater after left ventriculography with the ionic agents than with the nonionic agent. In those patients receiving nifedipine or diltiazem, the hypotensive response after bolus contrast angiography using the ionic agents occurred earlier after contrast injection (4.2 +/- 3.1 versus 12.9 +/- 6.0 seconds, p less than 0.0001), was more profound (maximal decrease in systolic arterial pressure, 48.5 +/- 13.9 versus 36.9 +/- 13.1 mm Hg, p less than 0.001) and was more prolonged (62.3 +/- 11.0 versus 36.4 +/- 12.0 seconds, p less than 0.0001) than in patients not receiving these drugs. A comparison of the two ionic contrast agents showed no significant difference in the hypotensive response. There was no difference in the hemodynamic response after angiography among patients receiving iopamidol alone and those receiving iopamidol and calcium antagonists. Thus, patients receiving the calcium antagonists diltiazem and nifedipine and undergoing left ventriculography with ionic contrast agents are at added risk for accentuation and prolongation of the hypotensive response.

Systemic, left ventricular and coronary hemodynamic effects of intravenous diltiazem in coronary artery disease

Systemic and coronary hemodynamic effects of intravenous diltiazem, administered as a bolus of 250 micrograms/kg followed by an infusion of 1.4 micrograms/kg/min, were examined in 14 patients with effort angina. There was no change in heart rate despite significant decreases in systolic, diastolic and mean systemic pressures (13%, 10% and 11%, respectively, all p less than 0.01). The blood pressure decrease was closely correlated with the initial blood pressure (r = 0.81, p less than 0.05). Neither left ventricular end-diastolic pressure nor peak dP/dt changed significantly, but peripheral vascular resistance decreased 16% (p less than 0.001) and stroke volume index increased 10% (p less than 0.05). The pressure-rate product decreased 15% (p less than 0.005), but coronary blood flow was maintained as coronary resistance decreased 14% (p less than 0.025). Diltiazem increased regional coronary flow in some patients. Thus, intravenous diltiazem dilates coronary and systemic resistance vessels, without an increase in heart rate, favorably altering indexes of myocardial oxygen supply and demand.