Efficacy of oral diltiazem to control ventricular response in chronic atrial fibrillation at rest and during exercise

2018 Korean Guideline of Atrial Fibrillation Management

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia in the general population. The Korean Heart Rhythm Society organized a Korean AF Management Guideline Committee and analyzed all available studies regarding the management of AF, including studies on Korean patients. This guideline is based on recent data of the Korean population and the recent guidelines of the European Society of Cardiology, European Association for Cardio-Thoracic Surgery, American Heart Association, and Asia Pacific Heart Rhythm Society. Expert consensus or guidelines for the optimal management of Korean patients with AF were achieved after a systematic review with intensive discussion. This article provides general principles for appropriate risk stratification and selection of anticoagulation therapy in Korean patients with AF. This guideline deals with optimal stroke prevention, screening, rate and rhythm control, risk factor management, and integrated management of AF.

Automatically finding relevant citations for clinical guideline development

OBJECTIVE

Literature database search is a crucial step in the development of clinical practice guidelines and systematic reviews. In the age of information technology, the process of literature search is still conducted manually, therefore it is costly, slow and subject to human errors. In this research, we sought to improve the traditional search approach using innovative query expansion and citation ranking approaches.

METHODS

We developed a citation retrieval system composed of query expansion and citation ranking methods. The methods are unsupervised and easily integrated over the PubMed search engine. To validate the system, we developed a gold standard consisting of citations that were systematically searched and screened to support the development of cardiovascular clinical practice guidelines. The expansion and ranking methods were evaluated separately and compared with baseline approaches.

RESULTS

Compared with the baseline PubMed expansion, the query expansion algorithm improved recall (80.2% vs. 51.5%) with small loss on precision (0.4% vs. 0.6%). The algorithm could find all citations used to support a larger number of guideline recommendations than the baseline approach (64.5% vs. 37.2%, p<0.001). In addition, the citation ranking approach performed better than PubMed's "most recent" ranking (average precision +6.5%, recall@k +21.1%, p<0.001), PubMed's rank by "relevance" (average precision +6.1%, recall@k +14.8%, p<0.001), and the machine learning classifier that identifies scientifically sound studies from MEDLINE citations (average precision +4.9%, recall@k +4.2%, p<0.001).

CONCLUSIONS

Our unsupervised query expansion and ranking techniques are more flexible and effective than PubMed's default search engine behavior and the machine learning classifier. Automated citation finding is promising to augment the traditional literature search.

[Rate versus rhythm control with and without heart failure]

Atrial fibrillation and congestive heart failure are frequently associated with complex interactions. Patients with both diseases bear a sophisticated therapeutic challenge for the attending physician. The approach to treat atrial fibrillation differs for patients with and without heart failure in several aspects. Basic requirements are the treatment of the underlying diseases and prophylaxis of thromboembolic complications. Rate and rhythm control are the two main therapeutic strategies for atrial fibrillation according to the current guidelines. Large trials including the recently published AF-CHF study (Atrial Fibrillation - Congestive Heart Failure) failed to demonstrate a difference in mortality for both strategies. Thus, the therapeutic decision is mainly based on the patient's symptoms to improve quality of life. Rate control should be applied to asymptomatic patients or if rhythm control has already failed. If beta-blockers and digoxin have failed to control heart rate, His ablation with pacemaker implantation can be considered. In patients without heart disease, class I antiarrhythmic drugs and, in case of ineffectiveness, amiodarone or catheter ablation are recommended for rhythm control. First data concerning catheter ablation of atrial fibrillation in heart failure are promising and randomized studies are on the way. Rhythm control remains first-line therapy in recent-onset or highly symptomatic paroxysmal or persistent atrial fibrillation patients with and without heart failure.

Heart rate control in patients with atrial fibrillation referred for exercise testing

Clinical practice guidelines for patients with atrial fibrillation (AF) recommended a heart rate (HR) of 60 to 80 beats/min at rest and 90 to 115 at moderate exercise. The degree to which HR control at rest and with exercise in patients with AF complies with these recommendations is unknown. HR at rest and at peak exercise was retrospectively examined in 1,097 consecutive patients with AF referred for exercise myocardial perfusion imaging. In a subgroup of 195 patients, HR was also measured at an intermediate "moderate" level. Median HR at rest was 80 beats/min, at the upper end of the recommended range of 60 to 80. Only patients administered a beta blocker (BB; 31%) had lower (p <0.001) median HRs at rest. Median HR at moderate exercise was 128 beats/min, higher than the range of 90 to 115 recommended by the guidelines. Only patients administered a BB had significantly reduced HRs (p <0.003) at moderate exercise. Median peak exercise HR was 147 beats/min. Forty-five percent of patients exceeded their age-predicted maximal HR. Patients administered BBs were significantly less likely (p <0.01) to exceed their age-predicted maximal HR. In conclusion, in patients with AF, HR control at rest and during exercise often did not comply with guideline recommendations. Regimens including a BB were more effective in achieving HR control.

Rate control in permanent atrial fibrillation

Guidelines on the use of digoxin are inconsistent with evidence from randomised trials

Rate control in atrial fibrillation: looking beyond the average heart rate

PURPOSE OF REVIEW

The aim of this article is to provide a perspective on rate control in atrial fibrillation which emphasizes patient wellbeing (exercise tolerance, symptoms, quality of life) over attempts to reduce resting or exercise heart rate to an arbitrary range.

RECENT FINDINGS

Recent trials of rhythm versus rate control strategies of treatment in patients with atrial fibrillation suggest that rate control is a viable first line strategy in many patients. The adverse consequences of atrial fibrillation with rapid ventricular response are partly due to factors other than rate itself, such as irregularity of ventricular response, and variable changes in autonomic nervous system output. Digoxin, calcium channel blockers, and beta-blockers cause a similar reduction in resting heart rate. Beta blockers are the most potent at reducing exercise heart rate, followed by calcium channel blockers and digoxin. Exercise tolerance is occasionally improved by digoxin, sometimes improved by calcium channel blockers and not improved by (and sometimes decreased by) beta-blockers. Information about quality of life with different rate control regimens is sparse.

SUMMARY

Rate control in atrial fibrillation provides important benefits to patients in terms of symptoms, quality of life and prevention of late consequences of uncontrolled rate (such as tachycardia induced cardiomyopathy). Restricting treatment objectives to achievement of a specific heart rate range on resting or exercise electrocardiogram may result in lack of patient benefit or worsened symptoms. Understanding the nuances of rate control when treating individual patients and interpreting existing evidence allows patients to experience the most benefit from this treatment strategy.

Rate versus rhythm control in the management of patients with atrial fibrillation

The management of patients with atrial fibrillation involves three main areas: anticoagulation, rate control and rhythm control. Importantly, these are not mutually exclusive of each other. Anticoagulation is necessary for patients who are at a high risk of stroke; for example, those who are older than 75 years, or those who have hypertension, severe left ventricular dysfunction, previous cerebrovascular events, or diabetes. It is now clear that patients who are at a high risk of stroke require long-term anticoagulation with warfarin regardless of whether a rate-control or rhythm-control strategy is chosen. One possible exception might be patients who are apparently cured with catheter ablation. Several published trials comparing rate-control and rhythm-control strategies for the treatment of patients with atrial fibrillation have shown no difference in mortality between these approaches. The patients enrolled in these studies were typically over 65 years of age. Data comparing rate and rhythm strategies in patients who are younger than 60 years of age are limited. For more elderly patients, it seems reasonable to consider rate control as a primary treatment option and to reserve rhythm control for those who do not respond to rate control. For younger patients, we prefer to start with a rhythm-control approach and to reserve rate-control approaches for patients in whom antiarrhythmic drugs, ablation, or both, do not ameliorate the symptoms.

The Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) study

OBJECTIVES

We sought to evaluate approaches used to control rate, the effectiveness of rate control, and switches from one drug class to another in the Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) study.

BACKGROUND

The AFFIRM study showed that atrial fibrillation (AF) can be treated effectively with rate control and anticoagulation, but drug efficacy to control rate remains uncertain.

METHODS

Patients (n = 2,027) randomized to rate control in the AFFIRM study were given rate-controlling drugs by their treating physicians. Standardized rate-control efficacy criteria developed a priori included resting heart rate and 6-min walk tests and/or ambulatory electrocardiographic results.

RESULTS

Average follow-up was 3.5 +/- 1.3 years. Initial treatment included a beta-adrenergic blocker (beta-blocker) alone in 24%, a calcium channel blocker alone in 17%, digoxin alone in 16%, a beta-blocker and digoxin in 14%, or a calcium channel blocker and digoxin in 14% of patients. Overall rate control was achieved in 70% of patients given beta-blockers as the first drug (with or without digoxin), 54% with calcium channel blockers (with or without digoxin), and 58% with digoxin alone. Adequate overall rate control was achieved in 58% of patients with the first drug or combination. Multivariate analysis revealed an association between first drug class and several clinical variables. There were more changes to beta-blockers than to the other two-drug classes (p < 0.0001).

CONCLUSIONS

Rate control in AF is possible in the majority of patients with AF. Beta-blockers were the most effective drugs. To achieve the goal of adequate rate control in all patients, frequent medication changes and drug combinations were needed.

Pilsicainide for conversion and maintenance of sinus rhythm in chronic atrial fibrillation: a placebo-controlled, multicenter study

BACKGROUND

Pilsicainide is a newly synthesized antiarrhythmic agent with class Ic properties. Various antiarrhythmic agents have been used to convert atrial fibrillation (AF) to sinus rhythm or decrease the rate of relapse of AF.

METHODS

We randomly assigned 62 patients with chronic AF to oral treatment of either a placebo (10 patients) or 150 mg/day of pilsicainide (52 patients) for 4 weeks before electrical cardioversion. Before oral administration of pilsicainide, 41 patients underwent transesophageal echocardiography to investigate whether there was thrombus formation in the heart chambers. Patients without pharmacologic defibrillation underwent direct current cardioversion to restore sinus rhythm. After successful cardioversion, all patients continued to receive pilsicainide and were monitored for up to 2 years.

RESULTS

Before cardioversion, 11 patients in the pilsicainide group (21%) reverted to sinus rhythm. No patients in the placebo group reverted to sinus rhythm. Direct current cardioversion was performed in 51 patients; however, 8 patients were not converted to sinus rhythm (5 patients receiving pilsicainide, 3 patients receiving placebo), and 3 patients needed intracardiac cardioversion to convert to sinus rhythm. Asymptomatic bradyarrhythmias were observed in 5 patients in the pilsicainide group. During the follow-up period, 33 patients (71%) in the pilsicainide group remained in sinus rhythm at 1 month; this number decreased to 23 patients (49%) at 3 months, 20 (43%) at 6 months, 16 (34%) at 12 months, 16 (34%) at 18 months, and 16 (34%) at 24 months. All patients receiving placebo continued to receive placebo after the cardioversion, and AF recurred a few days after cardioversion in all cases. No independent discriminant variables were identified in the groups between maintenance and nonmaintenance of sinus rhythm. Although no serious side effects regarding pilsicainide have been documented, one patient died of acute myocardial infarction, most likely not related to pilsicainide administration.

CONCLUSIONS

Pilsicainide is effective in restoring or maintaining sinus rhythm in patients with chronic AF lasting longer than an average duration of 22 months. No major adverse effects were observed.

Ventricular rate control in chronic atrial fibrillation during daily activity and programmed exercise: a crossover open-label study of five drug regimens

OBJECTIVES

We compared the effects of five pharmacologic regimens on the circadian rhythm and exercise-induced changes of ventricular rate (VR) in patients with chronic atrial fibrillation (CAF).

BACKGROUND

Systematic comparison of standardized drug regimens on 24 h VR control in CAF have not been reported.

METHODS

In 12 patients (11 male, 69+/-6 yr) with CAF, the effects on VR by 5 standardized daily regimens: 1) 0.25 mg digoxin, 2) 240 mg diltiazem-CD, 3) 50 mg atenolol, 4) 0.25 mg digoxin + 240 mg diltiazem-CD, and 5) 0.25 mg digoxin + 50 mg atenolol; were studied after 2 week treatment assigned in random order. The VR data were analyzed by ANOVA with repeated measures. The circadian phase differences were evaluated by cosinor analysis.

RESULTS

The 24-h mean (+/-SD) values of VR (bpm) were - digoxin: 78.9 +/- 16.3, diltiazem: 80.0+/-15.5, atenolol: 75.9+/-11.7, digoxin + diltiazem: 67.3+/-14.1 and digoxin + atenolol: 65.0+/-9.4. Circadian patterns were significant in each treatment group (p < 0.001). The VR on digoxin + atenolol was significantly lower than that on digoxin (p < 0.0001), diltiazem (p < 0.0002) and atenolol (p < 0.001). The time of peak VR on Holter was significantly delayed with regimens 3 and 5 which included atenolol (p < 0.03). During exercise, digoxin and digoxin + atenolol treatments resulted in the highest and lowest mean VR respectively. The exercise Time-VR plots of all groups were nearly parallel (p = ns). The exercise duration was similar in all treatment groups (p = ns).

CONCLUSIONS

This study indicates that digoxin and diltiazem, as single agents at the doses tested, are least effective for controlling ventricular rate in atrial fibrillation during daily activity. Digoxin + atenolol produced the most effective rate control reflecting a synergistic effect on the AV node. The data provides a basis for testing the effects of chronic suppression of diurnal fluctuations of VR on left atrial and ventricular function in CAF.

Effects of antiarrhythmic drugs on variability of ventricular rate and exercise performance in chronic atrial fibrillation complicated with ventricular arrhythmias

For conversion of atrial fibrillation to sinus rhythm and management of ventricular arrhythmias, antiarrhythmic drugs were frequently used. However, the effects of antiarrhythmic drugs on exercise performance and on the variability of ventricular rate were not available. This study included 37 patients who had chronic atrial fibrillation complicated with symptomatic ventricular arrhythmias. The patients were divided into three groups and received sotalol, propafenone, and procainamide, respectively. Before and after taking the drugs for 14 days, these patients received treadmill exercise test, 24 h Holter electrocardiogram, and tilt table test for evaluation of the exercise performance and the variability of ventricular rate (including the mean RR intervals, mRR, the standard deviation of RR intervals, SDRR, and the root mean square of the difference in successive RR intervals, rMSSD). All these antiarrhythmic drugs could suppress ventricular arrhythmia but only sotalol could significantly increase the exercise duration (374+/-50 to 476+/-55 s, P=0.02), and reduce the maximal heart rate (186+/-23 to 136+/-16 beats/min, P=0.01) during exercise test. Furthermore, only sotalol increased the mRR (777+/-60 to 885+/-66 ms, P=0.02), SDRR (190+/-40 to 216+/-48 ms, P=0.04) and rMSSD (223+/-48 to 253+/-40 ms, P=0.03) during 24 h Holter electrocardiogram. With head-up tilt, the mRR, SDRR and rMSSD all decreased significantly before drug therapy, and these changes were still present only after propafenone therapy. Therefore, comparisons among sotalol, propafenone and procainamide showed that sotalol increased the exercise performance and the variability of ventricular rate in patients who had chronic atrial fibrillation complicated with symptomatic ventricular arrhythmias.

Risk of complications of atrial fibrillation

Atrial fibrillation is associated with three major risk of complications: thromboembolism, hemodynamic compromise, and arrhythmogenesis. In patients with chronic atrial fibrillation the incidence of embolization is about 5% per year. The risk of embolism and in particular of stroke can be reduced by warfarin anticoagulation. Aspirin is generally less effective than warfarin, although it is probably more effective than placebo. The hemodynamic complications which may occur during atrial fibrillation are mainly due to the loss of effective atrial contraction, the irregular ventricular rhythm, and the possible excessively rapid ventricular rate. Sudden death is a recognized manifestation of Wolff-Parkinson-White syndrome and is considered to be precipitated by atrial fibrillation in the majority of patients. Torsades de pointes is perhaps the most widely recognized proarrhythmia associated with treatment of atrial fibrillation, especially with 1A antiarrhythmic drugs and sotalol. The chronic treatment with type 1C drugs in 3.5%-5% of patients may induce atrial flutter with 1:1 conduction with significant hemodynamic compromise.

Atrial fibrillation: maintaining stability of sinus rhythm or ventricular rate control? The need for prospective data: the PIAF trial

Atrial fibrillation is one of the most commonly encountered clinical arrhythmias. Different treatment options for this rhythm disorder exist with the electrical and/or pharmacological cardioversion to sinus rhythm with subsequent antiarrhythmic drug therapy to prevent recurrences being one of the primary therapeutic goals. Another alternative, however, is represented by the control of the ventricular rate in patients with persistent atrial fibrillation. The question of which these two strategies should be preferred in the majority of patients with atrial fibrillation has not been studied in a prospective way. Given the background of conflicting data with respect to the prognostic impact of atrial fibrillation and of the increasing evidence concerning the risks of antiarrhythmic drug treatment in atrial fibrillation, a prospective multicenter trial has been initiated to compare these two therapeutic alternatives prospectively. Patients will be randomly assigned to cardioversion with subsequent antiarrhythmic drug therapy to prevent recurrent atrial fibrillation or to a therapy aiming exclusively at control of the ventricular rate during persistent atrial fibrillation. All patients will receive anticoagulation by means of warfarin (target INR 2.5-3.5) to prevent thromboembolic complications. The rationale and the design of the PIAF trial (Pharmacological intervention in Atrial Fibrillation) are discussed below. The pilot phase of this study has begun patient enrollment in the spring of 1995.

Pharmacologic management of atrial fibrillation

In an era when many electrophysiologic problems are routinely treated with invasive procedures or implantable devices, drugs remain the cornerstones of treatment for atrial fibrillation. Atrial fibrillation may present as an episodic rhythm in patients who are primarily in sinus rhythm or it may be manifested as rhythm disorder that is permanent. Patients who appear to have an episodic rhythm disorder may be found to be in atrial fibrillation permanently when followed for long periods of time, and prognosis in the two forms is similar. It is, therefore, useful to consider them different manifestations in the same spectrum of disease. This review will address pharmacologic approaches designed to: (1) slow ventricular response; (2) restore sinus rhythm; (3) reduce occurrences of atrial fibrillation; and (4) prevent thromboembolic complications. Nonpharmacologic approaches to treating atrial fibrillation will be briefly reviewed.

Re-examining the clinical safety and roles of calcium antagonists in cardiovascular medicine

Despite recent analyses questioning the safety of calcium antagonists, evidence and clinical practice strongly support a major role for these drugs in the management of many cardiovascular diseases such as arrhythmia, vascular spasm, hypertension, diastolic dysfunction, stable angina, and myocardial infarction. These agents are a heterogeneous class of drugs with each formulation possessing unique properties and clinical applications. This article presents a review of the available literature and discusses the recommended use of various calcium antagonists in the treatment of diseases of the heart and vascular system.

Pharmacologic control of heart rate in atrial fibrillation

Atrial fibrillation is associated with a resting heart rate in excess of age-matched subjects in sinus rhythm, and there is an additional steep rise in rate during exertion. This article reviews the factors responsible for this tachycardia, the pharmacologic agents commonly used for heart rate control, and the effects of atrial antiarrhythmic agents on the heart rate during paroxysmal atrial fibrillation.

Mechanical and electrophysiological effects of 8-oxoberberine (JKL1073A) on atrial tissue

The effects of 8-oxoberberine (JKL1073A) on contractions and electrophysiological characteristics of atrial tissues were examined. In driven left atria of the rat JKL1073A (10-100 microM) increased twitch tension dose-dependently. In spontaneously beating right atria, JKL1073A increased twitch tension but decreased beating rate slightly. The positive inotropic and the negative chronotropic effect of 30 microM JKL1073A was not affected by prazosin (1 microM), propranolol (1 microM) and 3-isobutyl-1-methyl-xanthine (10 microM) but significantly suppressed by 4-aminopyridine (2 mM 4-AP). Current-clamp study revealed that JKL1073A prolonged rat atrial action potential duration (APD). This prolongation of APD by JKL1073A was decreased by pretreating the cells with 2 mM 4-AP. Voltage-clamp study showed that JKL1073A inhibited the integral of the transient outward current (I(to)) dose-dependently with a KD value of 3.66 +/- 0.93 microM in rat atrial myocytes. The equilibrium dissociation constant (Kd) for JKL1073A bindings to open state I(to) was 0.50 +/- 0.08 microM. The suppression of I(to) by 3 microM JKL1073A was accompanied by shortening of its inactivation time constant from 52.5 +/- 0.9 ms to 16.8 +/- 0.7 ms. V(0.5) for the steady-state inactivation curve of I(to) was shifted from -25.7 +/- 3.3 mV to -34.8 +/- 3.2 mV. In human atrial cells, similar inhibition of I(to) and prolongation of APD by JKL1073A was found. The KD value of JKL1073A for inhibition of the integral of I(to) in human atrial cells is 4.03 +/- 0.02 microM. The Kd for bindings to open state I(to) is 0.5 microM. Currents through K1 channels of rat and human atrial myocytes were not inhibited by JKL1073A at concentrations up to 10 microM. These results indicate that JKL1073A exerts a positive inotropic effect by inhibition of I(to). JKL1073A inhibit I(to) by binding to open state channels or shifting of the steady-state inactivation curve of I(to).

Pharmacokinetics and pharmacodynamics of intravenous diltiazem in patients with atrial fibrillation or atrial flutter

BACKGROUND

Diltiazem, a calcium channel blocker, has been shown to be safe and effective in the treatment of patients in atrial fibrillation and/or atrial flutter. However, there have been no pharmacokinetic/pharmacodynamic studies of diltiazem in these patients.

METHODS AND RESULTS

The pharmacokinetics and pharmacodynamics of intravenous diltiazem were determined in 32 patients with atrial fibrillation or atrial flutter (mean +/- SD age, 66 +/- 7 years; mean baseline heart rate, 131 +/- 10 beats per minute) after 20 mg or 20 mg followed by 25-mg bolus doses and a 10 and 15 mg/hr infusion for 24 hours. After the 10 and 15 mg/hr infusions of diltiazem, mean +/- SD elimination half-life was 6.8 +/- 1.8 and 6.9 +/- 1.5 hours, volume of distribution was 411 +/- 151.8 and 299 +/- 70.8 I, and systemic clearance was 42 +/- 12.4 and 31 +/- 8.3 l/hr, respectively. Percentages of the plasma concentrations of the principal metabolites desacetyldiltiazem and N-desmethyldiltiazem to diltiazem were < 15% and < 10%, respectively. Thirty of 32 patients maintained response throughout the 24-hour infusion of diltiazem. Using a sigmoidal Emax pharmacodynamic model, a strong relation (mean +/- SD r2, 0.78 +/- 0.2) was observed between plasma diltiazem concentration and percent heart rate reduction. Mean +/- SD Emax (maximum percent reduction in heart rate from baseline) and EC50 (plasma diltiazem concentration that achieves half Emax) were 52 +/- 17% and 110 +/- 84 ng/ml, respectively. The model predicts that mean plasma diltiazem concentration of 79, 172, and 294 ng/ml are required to produce a 20%, 30%, and 40% reduction in heart rate, respectively. A relation between plasma diltiazem concentration and percent change in systolic blood pressure (SBP) or diastolic blood pressure (DBP) from baseline was not observed (mean +/- SD r2, SBP/DBP: 0.35 +/- 0.24/0.36 +/- 0.2). There were no untoward side effects observed.

CONCLUSIONS

First, the pharmacokinetics of diltiazem in patients with atrial fibrillation or atrial flutter is nonlinear with an apparent dose-dependent decrease in systemic clearance with increasing infusion rate. Second, using a sigmoidal Emax model, there is a strong relation between plasma diltiazem concentration and percent heart rate reduction. Third, the plasma concentrations of the principal metabolites desacetyldiltiazem and N-desmethyldiltiazem are low and are not expected to contribute significantly to the pharmacodynamics of intravenous diltiazem in these patients.

Rate-dependent effects of diltiazem on human atrioventricular nodal properties

BACKGROUND

Tachycardia enhances the channel-blocking effects of antiarrhythmic drugs. In contrast to the extensive data regarding the rate-dependent effects of sodium channel blockers in humans, little is known about the frequency-dependent effects of calcium channel blockers on human atrioventricular (AV) nodal properties. Accordingly, the purpose of this study was to evaluate the importance of heart rate in modulating the electrophysiological effects of diltiazem in humans.

METHODS AND RESULTS

Electrophysiological studies were performed in 25 patients. Sinus node, atrial, and AV nodal function were evaluated at multiple atrial rates under control conditions and after administration of one of three intravenous doses of diltiazem designed to produce low, intermediate, and high stable plasma concentrations (designated doses 1, 2, and 3, respectively). Results were analyzed in terms of the longest and shortest cycle lengths obtainable in each patient under control and drug conditions. Plasma concentrations of diltiazem were stable and averaged 43 +/- 4, 73 +/- 6, and 136 +/- 11 ng/ml for doses 1, 2, and 3, respectively. Sinus node recovery time, intra-atrial conduction time, atrial effective refractory period, and HV interval were unaffected by diltiazem infusion. Effects of diltiazem were limited to changes in AV nodal parameters. Stable, dose-dependent increases in Wenckebach cycle length were observed after all three doses of diltiazem (increases of 54 +/- 13, 84 +/- 18, and 174 +/- 33 msec for doses 1, 2, and 3, respectively). Small nonsignificant increases in AH interval and atrioventricular effective refractory period (AVERP) were observed after dose 1 of diltiazem. At long cycle lengths, diltiazem caused modest increases in AH interval (3 +/- 4 and 25 +/- 8 msec for doses 2 and 3, respectively) and AVERP (36 +/- 12 and 70 +/- 25 msec). Drug effects were far greater at short cycle lengths (45 +/- 17 msec, 58 +/- 12 msec for AH interval and 80 +/- 24 msec, 163 +/- 41 msec for AVERP; p less than 0.05 versus values at long cycle lengths). At rapid rates, effects of diltiazem on AVERP substantially exceeded those on AV conduction, a result that could account for the beneficial effects of diltiazem during paroxysmal AV reentrant tachycardia by decreasing the excitable gap.

CONCLUSIONS

Depressant effects of diltiazem on human AV nodal function are highly dependent on atrial rate; the rate-dependent actions on AV nodal refractoriness probably contribute to beneficial effects of diltiazem in patients with supraventricular arrhythmias.

Effects of diltiazem, propranolol, and their combination in the control of atrial fibrillation

The effect of the combined treatment with propranolol 20 mg tid and diltiazem 60 mg tid in patients with chronic atrial fibrillation treated with digoxin was evaluated. Thirteen patients entered a double-blind, three-phase crossover study. Heart rate was significantly reduced during rest and at maximal exercise (p less than 0.05) during combined treatment compared with treatment with any single drug. No significant changes in maximal work load, exercise time, systolic blood pressure at maximal work load, or subjective sensation of well-being could be demonstrated during combined drug treatment. The RR distribution pattern was unaffected by the addition of propranolol, diltiazem, or their combination to the chronic digoxin treatment. It is concluded that the combination of diltiazem and propranolol has no advantages over any of these drugs singly, in the moderation of heart rate in patients with atrial fibrillation even combined with basic digitalis treatment, and that the intrinsic AV nodal function is unaffected by these drugs or their combination.

Role of calcium antagonists for heart rate control in atrial fibrillation

Atrial fibrillation is one of the most common symptomatic sustained arrhythmias seen in clinical practice. Many patients with atrial fibrillation and a ventricular response greater than 120 beats/min will experience cardiac symptoms. In the past, control of heart rate in these patients consisted of administration of intravenous digoxin, but this often proved to be ineffective or limited by toxicity. Recently, intravenous beta blockers such as esmolol have been used to slow the ventricular rate during atrial arrhythmias, but in some studies their use has been limited by hypotension. Alternatively, a bolus of an intravenous calcium antagonist, e.g., diltiazem or verapamil, may be administered to achieve acute slowing of the ventricular response. An intravenous bolus of diltiazem or verapamil may be effective, but use of either may be limited by its short duration of action and the inability to administer repeated boluses to tightly control or "fine tune" the heart rate. However, a new bolus plus maintenance infusion technique with diltiazem has shown promise in initial studies. It appears that in the future, continuous infusion techniques with intravenous calcium antagonists will be available that provide safe and effective sustained control of the ventricular response during atrial arrhythmias.

The drug treatment of atrial fibrillation

1. Atrial fibrillation is an inefficient cardiac rhythm associated with impaired exercise tolerance, exertional dyspnoea, palpitation and a substantial risk of thromboembolism. 2. The first decision in management is to consider cardioversion which can be achieved in suitable cases electrically, or pharmacologically with a class Ic antiarrhythmic drug like flecainide or propafenone. 3. Prophylaxis in paroxysmal atrial fibrillation is best achieved with a class Ic drug or a class III drug such as sotalol or amiodarone. 4. Control of ventricular rate in chronic atrial fibrillation can be achieved by pharmacological manipulation of the atrioventricular node by digoxin alone, or in combination with the calcium channel blockers verapamil or diltiazem, or beta-adrenoceptor blockers with intrinsic sympathomimetic activity like pindolol or xamoterol. 5. In view of the considerable risk of thromboembolism in patients with chronic atrial fibrillation anticoagulation or at least treatment with aspirin should be considered.

Influence of physical exercise on serum digoxin concentration and heart rate in patients with atrial fibrillation

Heart rate and serum digoxin concentration in eight patients with atrial fibrillation were studied at rest and during exercise when initial serum digoxin concentrations were zero and at low and high therapeutic values. Eight patients with ischemic heart disease and in sinus rhythm were studied for comparison. Though the serum digoxin concentration decreased significantly during exercise, the absolute reduction in heart rate was the same at rest and during exercise in patients with atrial fibrillation. Compared with the control patients in sinus rhythm, the heart rate in patients with atrial fibrillation was not adequately controlled during exercise by any serum digoxin concentration tested despite a reduction in heart rate with increasing digoxin concentration. The effects of digoxin on heart rate regulation in atrial fibrillation are complex and include direct effects on the myocardium as well as indirect effects mediated by modulation of the autonomic nervous system; the present results indicate that the drug is not displaced from the target organs by decreasing serum concentrations during exercise. In atrial fibrillation, because the demands on the filter function of the atrioventricular node are highly unphysiological, the effect of digoxin on heart rate during exercise is not adequate.

The pharmacologic treatment of atrial fibrillation

The pharmacologic treatment of atrial fibrillation (AF) is aimed at controlling the ventricular response, restoring sinus rhythm, and preventing or delaying relapses. In the control of ventricular response, digitalis maintains a primary role when the arrhythmia is accompanied by heart failure. In ischemic, hypertensive, and degenerative (whose number is increasing at present) cardiopathies without evident ventricular dilatation, treatments with calcium antagonists (such as verapamil, gallopamil, or diltiazem) or beta-blocking agents must be preferred. In order to control the ventricular response in patients with chronic AF during physical activity, the association of digitalis with beta-blocking agents or calcium antagonists seems to provide satisfactory results. The drugs of the IC class, especially flecainide, represent a certain therapeutical progress in the restoration of sinus rhythm in the treatment of paroxysmal atrial fibrillation affecting subjects without evident alterations of ventricular function, particularly in subjects with Wolff-Parkinson-White syndrome, with forms of vagal origin, or with atrial fibrillation alone. A therapeutic combination of digitalis and quinidine may produce resolution of the arrhythmia in the presence of altered ventricular function or when AF is of an uncertain onset. In patients with hypertensive, ischemic, and/or degenerative cardiopathy without evident ventricular or advanced heart failure, the verapamil-quinidine association may also be effective and even quicker. The combination of drugs of the I and III class for restoration of the sinus rhythm in particularly resistant forms of AF without evident structural heart alterations is promising but must be verified in a greater number of patients. In the prevention of relapses amiodarone appears to have the widest spectrum of advantages from an electrophysiologic point of view; however, because of its many side effects, amiodarone represents a late therapeutical choice. The promising results obtained with flecainide are disputed by the results of the CAST, which limit the possibilities of using this drug to a low number of cases (W.P.W. syndrome, AF of vagal origin, atrial fibrillation alone). In the past, quinidine and disopyramide have been the drugs most widely used in the prophylaxis of AF. These drugs have a similar efficacy, and both of them provided some positive results. However, because of untoward side effects (especially for quinidine) during chronic treatment, the use of these drugs has been questioned. Perhaps in the majority of patients, the less dangerous therapeutic choice after the termination of the fibrillation is a combination of drugs slowly down AV node activity (digitalis or calcium antagonists and beta blockers) with class IA antiarrhythmics.

Usefulness of labetalol in chronic atrial fibrillation

Beta-adrenergic blocking agents are useful in controlling excessive ventricular rate in chronic atrial fibrillation (AF) but often reduce exercise capacity. To investigate the advantage of labetalol--a unique beta blocker with alpha-blocking property--in chronic AF, 10 patients without underlying structural heart disease were studied with treadmill test, 12-minute walk and 24-hour ambulatory electrocardiographic monitoring. Patients were randomized and crossed over to receive 4 phases of treatment (placebo, digoxin, digoxin with half-dose labetalol, and full-dose labetalol). Exercise durations were 14.1 +/- 1.5, 14.2 +/- 1.5, 16.1 +/- 1.1 and 15.6 +/- 1.1 minutes, respectively, indicating that labetalol did not reduce exercise tolerance. Although digoxin had no advantage over placebo in controlling maximal heart rate (177 +/- 2 vs 175 +/- 3 beats/min), labetalol, both as monotherapy or as an adjunct to digoxin, was advantageous (156 +/- 4 vs 177 +/- 2 beats/min, p less than 0.01, and 154 +/- 4 vs 177 +/- 2 beats/min, p less than 0.01, respectively). The rate-pressure product was consistently lowered by labetalol at rest and during exercise. At peak exercise, the addition of labetalol to digoxin reduced the maximal rate-pressure product achieved from 30,900 +/- 1300 to 24,100 +/- 2,000 mm Hg/min (p less than 0.01) and the maximal rate-pressure product was lowest with full-dose labetalol (22,300 +/- 1,600 mm Hg/min). During submaximal exercise on treadmill or during the 12-minute walk, the combination of labetalol and digoxin produced the best heart rate control, whereas labetalol monotherapy was comparable to digoxin therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Ventricular rate control and exercise performance in chronic atrial fibrillation: effects of diltiazem and verapamil

The effects of two calcium channel blockers, diltiazem (270 mg/day) and verapamil (240 mg/day), were studied in 18 patients with chronic atrial fibrillation. During 24 h Holter electrocardiographic monitoring, mean ventricular rate (beats/min) decreased from 88 +/- 14 with placebo to 76 +/- 13 (p less than 0.001) with diltiazem and 80 +/- 11 (p less than 0.01) with verapamil. Maximal symptom-limited exercise tolerance (W) increased from 127 +/- 39 during the placebo period to 136 +/- 42 (p less than 0.01) with diltiazem and 137 +/- 39 (p less than 0.01) with verapamil. Ventricular rate and rate-pressure product were lower at rest and during exercise with diltiazem and verapamil than with placebo (p less than 0.001), with the drugs being similarly effective. Ventricular rate at maximal exercise (beats/min) was 179 +/- 13 with placebo compared with 159 +/- 21 with diltiazem and 158 +/- 23 with verapamil. Maximal oxygen uptake (ml/kg per min) was 22.3 +/- 4.5 with placebo, 23.7 +/- 4.9 (p less than 0.05) with diltiazem and 22.9 +/- 4.5 with verapamil (p = NS). Respiratory gas exchange anaerobic threshold was reached at a work load (W) of 76 +/- 21 with placebo, 84 +/- 27 (p less than 0.05) with diltiazem and 85 +/- 23 (p less than 0.01) with verapamil. In conclusion, patients with chronic atrial fibrillation have modestly improved exercise tolerance with calcium channel blockade therapy. The dromotropic responses and the effects on physical performance are of similar magnitude for diltiazem and verapamil.

Frequency-dependent effects of diltiazem on the atrioventricular node during experimental atrial fibrillation

Calcium channel blockers depress atrioventricular (AV) nodal properties in vivo in a frequency-dependent manner, suggesting that selective drug action during supraventricular arrhythmias may result from use-dependent properties. The present study was designed to examine whether or not the rate-dependent actions of diltiazem account for its therapeutic effects during atrial fibrillation. The determinants of the ventricular response to atrial fibrillation (concealed AV nodal conduction and AV node functional refractory period, AVFRP) were evaluated at multiple cycle lengths (with extrastimulus techniques) and during electrically induced atrial fibrillation (with indirect indexes from RR interval histograms) in anesthetized dogs. In the presence of diltiazem, AVFRP increased progressively relative to control as rate accelerated. At cycle lengths comparable to sinus rhythm in humans, AVFRP increased 10%, 17%, and 32% after doses 1, 2, and 3 of diltiazem, respectively. Drug-induced increases in AVFRP were greater at basic cycle lengths just above the Wenckebach point (17%, 48%, and 81%) and were maximal during atrial fibrillation (39%, 86%, and 154% increases for doses 1, 2, and 3, respectively). Diltiazem also increased the AV conduction system effective refractory period, thereby increasing the potential zone of concealment into the AV node. Frequency-dependent increases in the zone of concealment were produced by diltiazem and were associated with marked increases in the standard deviation of RR interval histograms during atrial fibrillation (257%, 526%, and 923% increases after doses 1, 2, and 3, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Efficacy and safety of intravenous diltiazem for treatment of atrial fibrillation and atrial flutter. The Diltiazem-Atrial Fibrillation/Flutter Study Group

This study evaluates the effectiveness and safety of intravenous diltiazem for the treatment of atrial fibrillation and atrial flutter. A double-blind, parallel, randomized, placebo-controlled protocol was used, and 6 large, urban hospitals, both university-affiliated and private, participated. The study involved 113 patients with atrial fibrillation or flutter, a ventricular rate greater than or equal to 120 beats/min and systolic blood pressure greater than or equal to 90 mm Hg without severe heart failure. The dose of intravenous diltiazem (or identical placebo) was 0.25 mg/kg/2 minutes followed 15 minutes later by 0.35 mg/kg/2 minutes if the first dose was tolerated but ineffective. If a patient did not respond, the code was broken and the patient was allowed to receive open-label diltiazem if placebo had been given. Of 56 patients, 42 (75%) randomized to receive diltiazem responded to 0.25 mg/kg and 10 of 14 responded to 0.35 mg/kg, for a total response rate of 52 of 56 patients (93%), whereas 7 of 57 patients (12%) responded to placebo (p less than 0.001). After the double-blind protocol, 49 of the 57 patients who received placebo were then given diltiazem; 47 of 49 responded, for an overall response rate of 99 of 105 patients (94%) with diltiazem. The median time from the start of drug infusion to the maximal decrease in heart rate was 4.3 minutes. Side effects occurred in 14 patients, 7 of whom had asymptomatic hypotension not requiring intervention. Thus, intravenous diltiazem was rapidly effective for slowing the ventricular response in most patients with atrial fibrillation or atrial flutter. Blood pressure decreased slightly. Side effects were mild.

Low- and medium-dose diltiazem in chronic atrial fibrillation: comparison with digoxin and correlation with drug plasma levels

The safety and efficacy of diltiazem were compared with digoxin maintenance therapy for control of ventricular response in 19 patients with chronic atrial fibrillation. The relationship between drug plasma levels and cardiovascular effects was also investigated. After 7 days of combined therapy with diltiazem (60 mg three times a day in 10 patients and four times a day in nine patients) and digoxin (0.125 mg/day in two patients and 0.250 mg/day in 17 patients), the 24-hour mean heart rate derived from ambulatory ECG recording was reduced by 16.3% in comparison with digoxin therapy alone; the serum digoxin level was not significantly changed (1.06 +/- 0.43 vs 1.05 +/- 0.61 ng/ml). After a standardized bicycle exercise test (50 watts for 3 minutes), maximal heart rate was reduced by 19.9%, diastolic blood pressure was decreased by 8.9%, and systolic pressure-rate product was decreased by 12.5%. Diltiazem plasma levels (mean 120.9 +/- 63.3 ng/ml) were linearly correlated with percentage variations in maximal heart rate, diastolic blood pressure, systolic blood pressure, and pressure-rate product during exercise. Eighteen patients in succession discontinued digoxin therapy; after 14 days of diltiazem alone, the 24-hour mean heart rate returned to control values of digoxin therapy, whereas maximal heart rate and pressure-rate product during exercise were significantly reduced (-17.2% and -14.1%, respectively), with no changes in blood pressure. Diltiazem plasma levels (135.0 +/- 83.2 ng/ml) showed a linear correlation with the percentage of reduction in maximal heart rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium channel antagonists. Part IV: Side effects and contraindications drug interactions and combinations

With the correct selection of drug and patient, the calcium antagonists as a group can be remarkably effective at relatively low cost of serious side effects. Almost all side effects are dose related. Minor side effects include those caused by vasodilation (flushing and headaches), constipation (verapamil), and ankle edema. Serious side effects are rare and result from improper use of these agents, as when intravenous verapamil (or diltiazem) is given to patients with sinus or atrioventricular nodal depression from drugs or disease, or nifedipine to patients with aortic stenosis. The potential of a marked negative inotropic effect is usually offset by afterload reduction, especially in the case of nifedipine which actually has the most marked negative inotropic effect. Yet caution is required when even calcium antagonists, especially verapamil, are given to patients with myocardial failure unless caused by hypertensive heart disease. Drug interactions of calcium antagonists occur with other cardiovascular agents such as alpha-adrenergic blockers, beta-adrenergic blockers, digoxin, quinidine, and disopyramide. The most marked interaction with digoxin is that with verapamil, which may raise digoxin levels by over 50%. Combination therapy of calcium antagonists with beta-blockers is increasingly common, and is probably safest in the case of dihydropyridines. Other combinations being explored are those with angiotensin-converting enzyme inhibitors and diuretics.

Calcium channel antagonists. Part III: Use and comparative efficacy in hypertension and supraventricular arrhythmias. Minor indications

The major antihypertensive mechanism of calcium antagonists is by decreasing the systemic vascular resistance, modified by the counter-regulatory responses of the baroreflexes and the renin-angiotensin-aldosterone system. In severe hypertension, the concept that calcium overload of the vascular myocyte could precipitate or aggravate peripheral vasoconstriction provides a logical basis for the use of these agents as first choice therapy; nifedipine, especially, has been well tested. As monotherapy for mild to moderate hypertension each of the three first-generation agents compares well with beta-blockers. Calcium antagonists may have a special role in the therapy of certain patient groups (elderly, black) or in those subjects whose life style involves intense physical or mental exertion (hemodynamics better maintained than with beta-blockade) or in patients with early end-organ damage such as left ventricular hypertrophy or renal insufficiency. However, the goal blood pressure may not be reached during monotherapy so that drug combinations may be required. Further indications for these compounds are as follows. Verapamil and diltiazem are frequently used in supraventricular tachycardias including acute and chronic atrial fibrillation. In the arrhythmias of the Wolff-Parkinson-White syndrome, there is the potential danger of provocation of anterograde conduction. Further indications for calcium antagonists, still under evaluation, include congestive heart failure (controversial), hypertrophic cardiomyopathy (verapamil), primary pulmonary hypertension (high doses required), Raynaud's phenomenon (nifedipine and diltiazem effective), peripheral vascular disease (proof not yet documented), cerebral insufficiency and subarachnoid hemorrhage (nimodipine promising), migraine, exertional bronchospasm, renal disease, atherosclerosis (experimental), and primary aldosteronism (nifedipine inhibits aldosterone release). Second-generation agents include dihydropyridines, such as nitrendipine, nicardipine, felodipine, amlodipine, nisoldipine, nimodipine, and isradipine. From these will be selected agents that are longer acting and provide higher vascular selectivity. New preparations of existing agents include slow-release formulations of nifedipine, verapamil, and diltiazem. Minor side effects include those caused by vasodilation (flushing and headaches), constipation (verapamil), and ankle edema. Serious side effects are rare and result from improper use of these agents, as when intravenous verapamil is given to patients with sinus or atrioventricular nodal depression from drugs or disease, or nifedipine to patients with aortic stenosis. The potential of a marked negative inotropic effect is usually offset by afterload reduction, especially in the case of nifedipine. Yet caution is required when calcium antagonists, especially verapamil, are given to patients with myocardial failure unless caused by hypertensive heart disease. Drug interactions of calcium antagonists occur with other cardiovascular agents such as alpha-adrenergic blockers, beta-adrenergic blockers, digoxin, quinidine, and disopyramide.(ABSTRACT TRUNCATED AT 400 WORDS)

Diltiazem and exercise performance in patients with chronic atrial fibrillation

To evaluate the influence of calcium entry blockade (diltiazem 60 mg qid) on exercise capacity in patients with chronic atrial fibrillation, nine men (mean age 65 years) with atrial fibrillation underwent maximal treadmill exercise on and off diltiazem therapy. Heart rate, blood pressure, and measured ventilatory parameters were assessed at a standard submaximal workload (3.0 mph/0% grade), the gas exchange anaerobic threshold (ATge), and maximal exercise. Significant reductions in heart rate at all stages of exercise were demonstrated: maximum heart rate decreased from 171 +/- 30 beats/min to 142 +/- 27 beats/min (17 percent, p less than .01) and submaximal exercise heart rate decreased from 123 +/- 22 beats/min to 96 +/- 16 beats/min (22 percent, p less than .01). However, there were no significant changes in blood pressure or gas exchange data, ie, oxygen uptake, minute ventilation, or respiratory exchange ratio at any of the exercise workloads. These data demonstrate that in patients with chronic atrial fibrillation, diltiazem controls the ventricular rate response throughout exercise without attenuating blood pressure or exercise capacity.