Towards improved control of atrial fibrillation

Advances in the management of atrial fibrillation with a special focus on non-pharmacological approaches to prevent thromboembolism: a review of current recommendations

Atrial fibrillation (AFIB) is the most common heart rhythm abnormality and is associated with significant morbidity and mortality. While the treatment of AFIB involves strategies of rate with or without rhythm control, it is also essential to strategize appropriate therapies to prevent thromboembolic complications arising from AFIB. Previously, anticoagulation was the main treatment option which exposed patients to higher than usual risk of bleeding. However, with the advent of new technology, novel therapeutic options aimed at surgical or percutaneous exclusion or occlusion of the left atrial appendage in preventing thromboembolic complications from AFIB have evolved. This review evaluates recent advances and therapeutic options in treating AFIB with a special focus on both surgical and percutaneous interventions which can reduce and/or eliminate thromboembolic complications of AFIB.

Digoxin for atrial fibrillation and atrial flutter: A systematic review with meta-analysis and trial sequential analysis of randomised clinical trials

Background

During recent years, systematic reviews of observational studies have compared digoxin to no digoxin in patients with atrial fibrillation or atrial flutter, and the results of these reviews suggested that digoxin seems to increase the risk of all-cause mortality regardless of concomitant heart failure. Our objective was to assess the benefits and harms of digoxin for atrial fibrillation and atrial flutter based on randomized clinical trials.

Methods

We searched CENTRAL, MEDLINE, Embase, LILACS, SCI-Expanded, BIOSIS for eligible trials comparing digoxin versus placebo, no intervention, or other medical interventions in patients with atrial fibrillation or atrial flutter in October 2016. Our primary outcomes were all-cause mortality, serious adverse events, and quality of life. Our secondary outcomes were heart failure, stroke, heart rate control, and conversion to sinus rhythm. We performed both random-effects and fixed-effect meta-analyses and chose the more conservative result as our primary result. We used Trial Sequential Analysis (TSA) to control for random errors. We used GRADE to assess the quality of the body of evidence.

Results

28 trials (n = 2223 participants) were included. All were at high risk of bias and reported only short-term follow-up. When digoxin was compared with all control interventions in one analysis, we found no evidence of a difference on all-cause mortality (risk ratio (RR), 0.82; TSA-adjusted confidence interval (CI), 0.02 to 31.2; I² = 0%); serious adverse events (RR, 1.65; TSA-adjusted CI, 0.24 to 11.5; I² = 0%); quality of life; heart failure (RR, 1.05; TSA-adjusted CI, 0.00 to 1141.8; I² = 51%); and stroke (RR, 2.27; TSA-adjusted CI, 0.00 to 7887.3; I² = 17%). Our analyses on acute heart rate control (within 6 hours of treatment onset) showed firm evidence of digoxin being superior compared with placebo (mean difference (MD), -12.0 beats per minute (bpm); TSA-adjusted CI, -17.2 to -6.76; I² = 0%) and inferior compared with beta blockers (MD, 20.7 bpm; TSA-adjusted CI, 14.2 to 27.2; I² = 0%). Meta-analyses on acute heart rate control showed that digoxin was inferior compared with both calcium antagonists (MD, 21.0 bpm; TSA-adjusted CI, -30.3 to 72.3) and with amiodarone (MD, 14.7 bpm; TSA-adjusted CI, -0.58 to 30.0; I² = 42%), but in both comparisons TSAs showed that we lacked information. Meta-analysis on acute conversion to sinus rhythm showed that digoxin compared with amiodarone reduced the probability of converting atrial fibrillation to sinus rhythm, but TSA showed that we lacked information (RR, 0.54; TSA-adjusted CI, 0.13 to 2.21; I² = 0%).

Conclusions

The clinical effects of digoxin on all-cause mortality, serious adverse events, quality of life, heart failure, and stroke are unclear based on current evidence. Digoxin seems to be superior compared with placebo in reducing the heart rate, but inferior compared with beta blockers. The long-term effect of digoxin is unclear, as no trials reported long-term follow-up. More trials at low risk of bias and low risk of random errors assessing the clinical effects of digoxin are needed.

Systematic review registration

PROSPERO CRD42016052935

Atrial fibrillation management: evaluating rate vs rhythm control

Atrial fibrillation (AF) is an increasing global issue leading to increased hospitalizations, adverse health related events and mortality. This review focuses on the management of atrial fibrillation, in particular in the past decade, comparing two major strategies, rate or rhythm control. We evaluate the evidence for each strategy, pharmacological options and the increasing utilization of invasive techniques, in particular catheter ablation and use of implantable cardiac pacing devices. Pharmacological comparative trials evaluating both strategies have shown rate control being non-inferior to rhythm control for clinical outcomes of mortality and other cardiovascular events (including stroke). Catheter ablation techniques, involving radiofrequency ablation and recently cryoablation, have shown promising results in particular with paroxysmal AF. However, persistent AF provides ongoing challenges and will be a particular focus of continued research.

Long-term management of atrial fibrillation

In the past decade, catheter ablation techniques and implantable devices have revolutionized the treatment of ventricular arrhythmias, junctional arrhythmias, and atrial flutter. For most patients presenting with atrial fibrillation (AF), the treatment available today is similar to that used a century ago, although nonpharmacologic strategies of therapy have begun to emerge for selected cases. There have been important recent advances in our understanding of the pathophysiology of AF and its complications, and it may be possible to improve patient management by refinement of the way in which current drugs are used.

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.

Relation between achieved heart rate and outcomes in patients with atrial fibrillation (from the Atrial Fibrillation Follow-up Investigation of Rhythm Management [AFFIRM] Study)

Many patients with atrial fibrillation (AF) are treated with rate control and anticoagulation. However, the relation between the degree of heart rate (HR) control and clinical outcome is uncertain. We assessed whether lower achieved HR at rest and/or lower achieved exercise HR was associated with improved prognosis, quality of life (QoL), and functional status among patients in the AFFIRM study. Patients in the rate control arm and who were in AF at baseline and 2 months were included. Patients were grouped by quartile of achieved HR at rest (44 to 69, 70 to 78, 79 to 87, 88 to 148 beats/min) and achieved exercise HR following a 6-minute walk (53 to 82, 83 to 92, 93 to 106, 107 to 220 beats/min). QoL measurements and functional status were also analyzed. Complete data were available for 680 patients for achieved HR at rest, 349 patients for achieved exercise HR, and 118 patients for QoL. Survival free from cardiac hospitalization and overall survival were not significantly different among quartiles of achieved HR at rest (p = 0.19 and p = 0.8, respectively) or achieved exercise HR (p = 0.77 and p = 0.14, respectively). After controlling for covariates, there remained no significant relation between either achieved HR at rest or achieved exercise HR and event-free survival (hazard ratio 0.95, p = 0.35 and hazard ratio 0.98, p = 0.81) or overall survival (hazard ratio 1.03, p = 0.70 and hazard ratio 1.22, p = 0.13). Furthermore, there was no significant association between achieved HR and QoL measurements, New York Heart Association functional class, or 6-minute walking distance. After 2 months of drug titration, neither achieved HR at rest nor achieved exercise HR predicted survival free from cardiovascular hospitalization, overall survival, QoL, or functional status among patients with AF.

Rate control in atrial fibrillation: choice of treatment and assessment of efficacy

The clinical relevance and high social costs of atrial fibrillation have boosted interest in rate control as a cost-effective alternative to long-term maintenance of sinus rhythm (i.e. rhythm control). Prospective studies show that rate control (coupled with thromboembolic prophylaxis) is a valuable treatment option for all forms of atrial fibrillation. The rationale for rate control is that high ventricular rates, frequently found in atrial fibrillation, lead to haemodynamic impairment, consisting of a variable combination of loss of atrial kick, irregularity in ventricular response and inappropriately rapid ventricular rate, depending on the type of underlying heart disease. Long-term persistence of tachycardia at a high ventricular rate can lead to various degrees of ventricular dysfunction and even to tachycardiomyopathy-related heart failure. Identification of this reversible and often concealed form of left ventricular dysfunction can permit effective management by rate (or rhythm) control. Although acute rate control (to reduce ventricular rate within hours) is still often based on digoxin administration, for patients without left ventricular dysfunction, calcium channel antagonists or beta-adrenoceptor antagonists (beta-blockers) are generally more appropriate and effective. In chronic atrial fibrillation, long-term rate control (to reduce morbidity/mortality and improve quality of life) must be adapted to patients' individual characteristics to grant control during daily activities, including exercise. According to current guidelines, the clinical target of rate control should be a ventricular rate below 80-90 bpm at rest. However, in many patients, assessment of the appropriateness of different drugs should include exercise testing and 24h-Holter monitoring, for which specific guidelines are needed. In practice, rate control is considered a valid alternative to rhythm control. Recent prospective trials (e.g. the Pharmacological Intervention in Atrial Fibrillation [PIAF] and the Atrial Fibrillation Follow-up Investigation of Rhythm Management [AFFIRM] trials) have shown that in selected patients, rate control provides similar benefits, more economically, in terms of quality of life and long-term mortality. The choice of a rate control medication (digoxin, beta-blockers, calcium channel antagonists or possibly amiodarone) or a non-pharmacological approach (mainly atrioventricular node ablation coupled with pacing) must currently be based on clinical assessment, which includes assessing the presence of underlying heart disease and haemodynamic impairment. Definite guidelines are required for each different subset of patients. Rate control is particularly tricky in patients with heart failure, for whom non-pharmacological options can also be considered. The preferred pharmacological options are beta-blockers for stabilised heart failure and digoxin for unstabilised forms.

Current management of symptomatic atrial fibrillation

Atrial fibrillation (AF) is the commonest arrhythmia. It presents in distinct patterns of paroxysmal, persistent and chronic AF, and patient management aims differ according to the pattern. In paroxysmal AF, drug treatment with beta-blockers, class Ic and class III agents reduce the frequency and duration of episodes. In persistent AF (recent onset, non-paroxysmal), early cardioversion with either pharmacological agents or by direct current (DC) cardioversion should be actively considered, in those patients who are suitable. Patients most likely to cardiovert and remain in sinus rhythm include those with duration of AF of <1 year, an acute reversible cause, left atrial diameter <50 mm and good left ventricular function on echocardiography. Recent data show that maintenance of sinus rhythm after successful cardioversion is enhanced by the use of class III drugs including amiodarone and dofetilide. In chronic or permanent AF, management is aimed at controlling the ventricular rate response with combinations of digoxin, beta-blockers and calcium antagonists with atrio-ventricular nodal activity (diltiazem and verapamil). There is some debate about the prognostic significance of AF. Certainly AF is associated with an excess mortality but this is largely accounted for by its association with serious intrinsic heart disease and the thrombo-embolic complications of the arrhythmia. Atrial fibrillation is a common default arrhythmia for the sick heart.

Effect of intravenous magnesium on heart rate and heart rate variability in patients with chronic atrial fibrillation

The present double-blind, placebo-controlled study investigated the effects of intravenous magnesium on heart rate and rate variability in 30 patients with chronic atrial fibrillation. During standardized conditions, intraindividual variation in heart rate and rate variability was low in patients with chronic atrial fibrillation and magnesium had no effect on heart rate or rate variability.

Safety of oral propafenone in the conversion of recent onset atrial fibrillation to sinus rhythm: a prospective parallel placebo-controlled multicentre study

AIM

Oral propafenone is effective in restoring sinus rhythm however the proarrhythmic effects are still unknown. The Safety Antiarrhythmic Therapy Evaluation (SATE) trial was a prospective randomized placebo-controlled multicentre study which evaluated the safety of acute oral loading dose of propafenone in patients with recent onset atrial fibrillation. Secondary end-points were to evaluate the effect of digitalis added to propafenone in ventricular rate control and the efficacy of propafenone alone or added to digitalis compared with efficacy of digitalis plus quinidine.

METHODS AND RESULTS

246 patients (126 male; 58+/-11 years) with atrial fibrillation of <48 h duration were randomly allocated to one of four groups: digitalis 0.75-1 mg i.v. plus quinidine 1100 mg (D+Q, 70 patients); propafenone 450-600 mg orally (PNF, 66 patients); propafenone 450-600 mg orally plus digitalis 0.750-1 mg i.v. (PNF+D, 70 patients); placebo (Pl, 40 patients). All patients underwent 24-h ECG Holter monitoring. Safety was assessed by evaluating the appearance of adverse events classified as mild, moderate and severe. No severe adverse events were reported. Short lasting asymptomatic atrial flutter episodes with atrio-ventricular conduction > or =2:1 were observed in 14% of the D+Q group, 21% PNF, 18% PNF+D and in 8% Pl. One patient in the D+Q group and four in the PNF+D group showed asymptomatic runs of 3-4 ventricular ectopic beats. Reversible sinus atrial blocks (<3 s) were detected in two patients of the D+Q group and in two of the PNF group. In patients with persistent atrial fibrillation the ventricular rate was similar in the four study groups. At 3 h the high efficacy of propafenone was confirmed. At the 24th hour no differences were found between active treatment and placebo arms.

CONCLUSION

Propafenone in a single oral loading dose is safe and promptly effective in patients with recent onset atrial fibrillation.

Atrial fibrillation: maintenance of sinus rhythm versus rate control

Atrial fibrillation represents a common and challenging arrhythmia. A rational approach to management of the individual case depends on careful assessment of the temporal of the arrhythmia, any associated cardiovascular disease, and any particular features suggesting the advisability or risks of any particular treatment regimen. The nature of an arrhythmia and of individual patient factors change over time, requiring a flexible approach to long-term treatment that may be defined only after months or years. While new treatment options such as catheter ablation techniques and implantable atrial defibrillators are being tested, old therapies (e.g., low-dose amiodarone) are undergoing reappraisal. Increasing recognition of the dangers of antiarrhythmic therapy used to maintain sinus rhythm is focusing attention on nonpharmacologic methods. All patients with persistent atrial fibrillation merit serious consideration for direct current cardioversion before accepting that atrial fibrillation is permanent, and many patients may benefit from more than one attempt to restore and maintain sinus rhythm.

Comparative study of efficacy and safety of low-dose diltiazem or betaxolol in combination with digoxin to control ventricular rate in chronic atrial fibrillation: randomized crossover study

BACKGROUND

The combination therapy of low-dose diltiazem or bexatolol with digoxin can be a useful adjunct for achieving heart rate control with minimal side effects. But there has not been a study including patients with impaired left ventricular function and evaluating whether the beneficial effects of medication will be maintained during a follow-up period.

OBJECTIVES

The purpose of this study was three-fold: (1) to compare the efficacy of digoxin with low-dose diltiazem and digoxin with low-dose betaxolol on randomized crossover study; (2) to evaluate whether the beneficial effects of medication will be maintained after 7 months; (3) to evaluate the safety of the combination therapy in patients with impaired left ventricular function.

METHODS

We did a prospective randomized crossover study in 35 patients with chronic atrial fibrillation (AF) including 15 patients with left ventricular dysfunction. After enrollment, each patient was evaluated for heart rate, blood pressure, rate-pressure products, maximal exercise tolerance at rest and during symptom-limited treadmill test before medication, at 4 weeks after medication of digoxin (0.125-0.5 mg daily) with diltiazem (90 mg twice daily), and at 4 weeks after digoxin with betaxolol (20 mg once daily). We performed 24-h ambulatory electrocardiogram (ECG) in 15 patients at the end of each phase of treatment. We repeated symptom-limited treadmill test like above method in 15 patients at 7 months of medication.

RESULTS

(1) Ventricular rates were significantly reduced in digoxin with low-dose betaxolol therapy at rest and during exercise (67 +/- 3, 135 +/- 5 (mean +/- S.E.M.) beats/min, respectively) in comparison to digoxin with low-dose diltiazem therapy (80 +/- 7, 154 +/- 5) (P < 0.05). (2) Rate-pressure products were significantly less in digoxin with low-dose betaxolol at rest and during exercise (85 +/- 4, 213 +/- 12 x 10(2) mmHg/min) than in digoxin with low-dose diltiazem therapy (105 +/- 6, 269 +/- 12) (P < 0.05). (3) Exercise capacity was significantly improved in digoxin with low-dose betaxolol (9.3 +/- 0.5 METS) or digoxin with low-dose diltiazem (9.7 +/- 0.5) in comparison to control state (8.3 +/- 0.5) (P < 0.05). (4) At 7 months evaluation, there was no significant difference between at 4 weeks and at 7 months. (5) Results on 24-h ambulatory ECG showed the same findings as on treadmill test. (6) Although side effects occurred more frequently in digoxin with low-dose betaxolol therapy, they were minimal and no patient had to withdraw medication. Worsening of left ventricular dysfunction was not observed.

CONCLUSION

Our study suggested that (1) combination therapy of low-dose betaxolol with digoxin was more superior to low-dose diltiazem with digoxin in controlling ventricular rate and reducing rate-pressure products; (2) the effects controlling ventricular rate, reducing rate-pressure products and improving exercise capacity have been well maintained even after 7 months of medication with each combination therapy.

Electrophysiologic determinants of ventricular rate in human atrial fibrillation

INTRODUCTION

The mechanisms of the ventricular response during atrial fibrillation (AF) remain uncertain. The parameters obtained during an electrophysiologic study, including atrial rates during AF, were analyzed to clarify further the determinants of the ventricular rate during AF.

METHODS AND RESULTS

Thirty patients without manifest preexcitation in whom AF was induced during electrophysiologic study were divided into two groups. Group 1 consisted of 20 patients (ages 55 +/- 10 years) without a dual AV nodal pathway. Group 2 consisted of 10 patients (ages 53 +/- 13 years) having a dual AV nodal pathway. The correlation coefficient between the mean RR interval during AF (mRR) and the mean intra-atrial potential interval during AF (mff) was positive (0.05 [P < 0.05] in group 1 and 0.37 [P = NS] in group 2). The correlation coefficient of the mRR against the functional refractory periods of the AV node (AVFRP) was 0.73 (P < 0.001) in group 1. The correlation coefficients between mRR and the fast AV nodal pathway functional refractory periods and the slow AV nodal pathway effective refractory periods (SPERP) were 0.58 (P = NS) and 0.7 (P < 0.05) in group 2, respectively. The correlation coefficients between mRR against (mff x AVFRP)1/2 in group 1 and (mff x SPERP)1/2 in group 2 were 0.8 (P < 0.001) and 0.72 (P < 0.05), respectively.

CONCLUSIONS

This clinical study did not indicate an inverse relation between the atrial and ventricular rates that had been reported by the previous experimental study. The ventricular rate during AF appeared to be quantitatively related to the atrial rate via AV node function. The importance of the slow pathway in determining the ventricular rate during AF was observed.

Diurnal variation of ventricular response to atrial fibrillation in patients with advanced heart failure

Variability of ventricular rate was quantified by two measures of heart rate variability: the SD of the mean R-R interval (SDNN) and the SD of the 5-minute mean R-R interval (SDANN). In 35 patients with atrial fibrillation and advanced heart failure (left ventricular ejection fraction 20% +/- 9%, cardiac index 2.4 +/- 0.7 L/min/m2), SDNN and SDANN were compared to 13 preselected clinical and hemodynamic variables for prediction of outcome. During a 12-month follow-up period, 8 (23%) patients deteriorated clinically; 3 (9%) died, and 5 (14%) underwent heart transplantation. SDNN and SDANN correlated to the difference of the mean R-R interval between night (2 AM to 3 PM) and day (11 AM to noon) with r values of 0.62 and 0.77, respectively. From 15 preselected variables, only SDANN (chi 2 = 6.7, p = 0.01) was independently associated with survival on multivariate analysis. Dichotomized SDANN at 100 msec accurately predicted 12-month survival in 28 (80%) patients (relative risk = 9.77, p = 0.001). In conclusion, analysis of heart rate variability is useful in quantifying diurnal variation of ventricular rate in atrial fibrillation and might be useful in predicting survival in patients with advanced heart failure.

Beta-adrenoceptor blockers in atrial fibrillation: the importance of partial agonist activity

1. The ideal drug treatment for atrial fibrillation will control resting heart rate, blunt exercise induced tachycardia whilst not exacerbating nocturnal bradycardia. Monotherapy with digoxin may not be ideal. We have compared the effect of combining digoxin (0.25 mg daily) with atenolol 50 mg and 100 mg or pindolol 5 mg twice daily and 15 mg twice daily in a cross-over randomised single-blind trial in eight symptomatic patients (six male; mean age 62 years) with poorly controlled atrial fibrillation. 2. Heart rate control was measured by 24 h ECG at baseline on digoxin therapy and after 2 weeks with each treatment. Symptom scores for breathlessness and palpitation were measured using visual analogue scales. 3. The addition of both beta-adrenoceptor blockers significantly reduced mean diurnal maximum heart rate from baseline (all P < 0.001 ANOVA). Atenolol at both doses caused a greater reduction than either dose of pindolol (P < 0.001 ANOVA). Nocturnal maximum heart rate was not significantly reduced from baseline by either beta-adrenoceptor blocker, but both doses of pindolol caused increases in nocturnal maximum heart rate compared with atenolol (P < 0.001 ANOVA). 4. Atenolol caused a reduction in diurnal minimum heart rate compared with baseline and caused a reduction in nocturnal minimum heart rate whereas pindolol caused an increase (P < 0.001 ANOVA). 5. Atenolol 100 mg caused longer nocturnal pauses compared with baseline but pindolol 15 mg twice daily reduced the number of nocturnal pauses > 1.5 s (P = 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Placebo controlled trial of xamoterol versus digoxin in chronic atrial fibrillation

Thirteen patients in chronic atrial fibrillation with a normal resting heart rate but with exercise tachycardia and episodes of bradycardia were randomised to treatment periods of two weeks on xamoterol (200 mg twice daily), low dose digoxin, or placebo, in a blind crossover study. The results (mean SEM) of symptom scores, a treadmill exercise test, and 24 hour ambulatory electrocardiographic monitoring were obtained. Xamoterol improved symptom scores and controlled exercise heart rate better than digoxin. Xamoterol was better than digoxin or placebo in reducing the heart rate response to exercise and tended to improve exercise duration. Xamoterol, by reducing the daytime maximum hourly heart rate and increasing the night time minimum hourly heart rate, significantly reduced the difference between the two compared with placebo. In contrast, digoxin tended to reduce both the maximum and minimum hourly heart rates through day and night. Both the frequency and duration of ventricular pauses were reduced by xamoterol but tended to increase with digoxin. Xamoterol reduced both the circadian variation in ventricular response to atrial fibrillation and exercise tachycardia by modulating the heart rate according to the prevailing level of sympathetic activity. These changes were translated into symptomatic benefit for the patients studied.

What is meant by a "controlled" ventricular rate in atrial fibrillation?

Reduction of a rapid ventricular rate in atrial fibrillation results in a longer diastolic filling period and a higher left ventricular stroke volume but this is offset by reduced contractility and fewer beats per minute; the net effect on cardiac output is uncertain. Sequences of stroke distances were measured by Doppler ultrasound in 60 resting patients with atrial fibrillation to determine the relation between ventricular rate and linear cardiac output. The slope of the cardiac output/ventricular rate relation was positive in all 20 patients with a ventricular rate less than 90 beats per minute and negative in 16 (40%) of 40 patients with a ventricular rate greater than 90 beats per minute. In atrial fibrillation the ventricular rate can be regarded as "controlled" when the cardiac output/ventricular rate slope is positive and "uncontrolled" when the slope is negative--that is when reduction of ventricular rate would lead to increased cardiac output. As so defined, ventricular rate at rest was controlled in every patient when the ventricular rate was less than 90, controlled in 44 (73%) patients when the ventricular rate was 90-140 beats per minute, and uncontrolled in every case when it was greater than 140 beats per minute. Achieving a target ventricular rate of 90 beats per minute in patients with atrial fibrillation at rest would result in control with the least compromise of cardiac output.

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)