Concentration dependence of class III and beta-adrenergic blocking effects of sotalol in anesthetized dogs

Spontaneous pre-excited supraventricular tachycardias in a Labrador Retriever

A four-year-old Labrador Retriever was presented for intermittent tachycardia. The electrocardiogram showed sinus rhythm conducted with ventricular pre-excitation and short runs of orthodromic atrioventricular reciprocating tachycardia. Four months later, the rhythm degenerated into a symptomatic sustained tachycardia, suspected to be pre-excited atrial fibrillation, a potentially life-threatening rhythm in the presence of an accessory pathway with a short refractory period. Two days after initiating oral diltiazem, the dog deteriorated and represented with sustained orthodromic atrioventricular reciprocating tachycardia, which was terminated by a precordial chest thump. It proceeded to sinus rhythm with ventricular pre-excitation followed by an episode of pre-excited focal atrial tachycardia. A bolus of lidocaine IV successfully restored sinus rhythm and sotalol treatment was started. The dog clinically recovered but died spontaneously 24 h later. This is the first case report that describes spontaneous pre-excited focal atrial tachycardia.

Single- and multiple-dose pharmacokinetics of sotalol hydrochloride in healthy cats

INTRODUCTION/OBJECTIVES

The objective of this study was to describe the single- and multiple-dose pharmacokinetics and urinary elimination of sotalol in healthy cats.

ANIMALS

Six adult purpose-bred cats MATERIALS AND METHODS: Cats were administered 2 mg sotalol/kg body weight as a single intravenous bolus and as a single oral dose in a randomized crossover study with a 2-week washout period. The same cats then received 3 mg sotalol/kg orally every 12 h for 2 weeks. Blood samples were collected at predetermined time points for 48 h postdose for quantification of sotalol using ultra-high-pressure liquid chromatography with mass spectrometry. Non-compartmental analysis was used to obtain pharmacokinetic parameters. Data are presented as median (min-max).

RESULTS

Following intravenous administration, plasma clearance and volume of distribution were 9.22 mL/min/kg (5.69-10.89) and 2175.56 (1961-2341.57) mL/kg, respectively. Bioavailability was 88.41% (62.75-130.29) following a single oral dose. Peak plasma concentration (Cmax) and time to Cmax were 0.94 μg/mL (0.45-1.17) and 1.5 h (0.5-4) after a single oral dose (2 mg/kg), and 2.29 μg/mL (1.91-2.48) and 1.0 h (0.5-1.5) with chronic oral dosing (3 mg/kg), respectively. Elimination half-life was 2.75 h (2.52-4.10) and 4.29 h (3.33-5.53) for single and chronic oral dosing, respectively. Accumulation index was 1.17 (1.09-1.29) after chronic dosing. Urinary sotalol recovery was 81-108% of the intravenous dose.

CONCLUSIONS

Oral sotalol administration resulted in plasma concentrations reportedly efficacious in other species, with good to excellent oral bioavailability. Urinary excretion appears to be a major route of elimination. Following repeated oral dosing, minimal drug accumulation was estimated. Additional studies in cats are recommended due to the possibility of nonlinear kinetics.

Association of sotalol versus atenolol therapy with survival in dogs with severe subaortic stenosis

INTRODUCTION/OBJECTIVES

Dogs with severe subaortic stenosis (SAS) are at risk of dying suddenly from fatal arrhythmias. Survival is not improved when treated with pure beta-adrenergic receptor (β)-blockers; however, the effect of other antiarrhythmic drugs on survival is unknown. Sotalol is both a β-blocker and a class III antiarrhythmic drug; the combination of these differing mechanisms may provide benefit to dogs with severe SAS. The primary objective of this study was to compare survival in dogs with severe SAS that were treated with either sotalol or atenolol. The secondary objective was to evaluate the effect of pressure gradient (PG), age, breed, and aortic regurgitation on survival.

ANIMALS

Forty-three client-owned dogs.

MATERIALS AND METHODS

Retrospective cohort study. Medical records of dogs diagnosed with severe SAS (PG ≥ 80 mmHg) between 2003 and 2020 were reviewed.

RESULTS

No statistical difference was identified in survival time between dogs treated with sotalol (n = 14) and those treated with atenolol (n = 29) when evaluating all-cause mortality (p=0.172) or cardiac-related mortality (p=0.157). Of the dogs that died suddenly, survival time was significantly shorter in dogs treated with sotalol compared to those treated with atenolol (p=0.046). Multivariable analysis showed that PG (p=0.002) and treatment with sotalol (p=0.050) negatively influenced survival in the dogs that died suddenly.

CONCLUSIONS

Sotalol did not have a significant effect on survival overall but may increase the risk of sudden death in dogs with severe SAS compared to atenolol.

Non-invasive telemetric electrocardiogram assessment in conscious beagle dogs

INTRODUCTION

The primary objective of this investigation was to evaluate the sensitivity of a non-invasive telemetry system for the detection of drug-induced electrocardiogram (ECG) changes in conscious, freely moving dogs. A secondary objective was to compare, in the same set of dogs, ECG data acquired by a non-invasive system with data acquired from a surgically implanted telemetry device (invasive system).

METHODS

Continuous beat-to-beat Lead II ECG data were simultaneously acquired from 6 male dogs using a non-invasive and an invasive telemetry system for 1h pre-dose and 6h following a sham control dose or single oral doses of (+/-) sotalol (4, 8 or 16 mg/kg). ECG parameters of heart rate, RR, PQ, QRS, QT and QT corrected for heart rate according to Van de Water (QTcV) and by an individual linear regression formula (QTcR), were determined.

RESULTS AND DISCUSSION

Statistically significant dose-dependent reduction of heart rate, and increases in PQ, QT and QTc (V and R) were detected at all dose levels of (+/-) sotalol, with partial recovery during the 6-hour monitoring period. Statistically significant correlations for heart rate, RR, PQ, QT and QTc (V and R) were found between the two systems. QRS duration did not correlate. However, the difference between the two systems was consistent over the range studied. Based on these findings, the non-invasive system is quantitatively comparable to invasive telemetry, and can be used successfully to acquire continuous ECG data on a beat-to-beat basis from conscious freely moving dogs for at least 6h post-dose.

β-Blockers for the treatment of cardiac arrest from ventricular fibrillation?

More than 160,000 people suffer sudden cardiac death each year in the US. It is estimated that ventricular fibrillation (VF) is the initial rhythm in approximately 30% of these cases. Ventricular fibrillation that does not respond to the first few defibrillation attempts is associated with mortality rates of up to 97%. Currently, no pharmacological intervention has been shown to increase long-term survival in patients with shock-refractory VF. The purpose of this review article is to evaluate whether beta-blocker administration during the resuscitation of cardiac arrest from VF or pulseless ventricular tachycardia (VT) improves outcome. We searched the MEDLINE and EMBASE databases for human clinical trials, animal experimental trials, review articles, case reports and abstracts published between 1966 and September 2006. No human prospective randomized controlled trial has studied the effects of beta-blocker administration during VF directly. Prospective trials of anti-arrhythmics with beta-blocking properties have been published, as well as several case reports/case series and experimental animal studies. The evidence thus far suggests that beta-blockade during resuscitation from VF may be associated with increasing rates of resuscitation, greater post-resuscitation survival, and improved post-resuscitation myocardial function. These positive effects on outcome may be mediated by a decrease in the oxygen requirements of the fibrillating heart, thus improving the overall balance between myocardial oxygen supply and demand during resuscitation. While no significant detrimental effects directly related to low dose beta-blockade during VF have been reported in the studies reviewed, concerns relating to possible loss of myocardial contractility and hypotension remain. To this day, high quality human trials are lacking. Preliminary human studies are needed to assess the effects of beta-blockers in the treatment of cardiac arrest from ventricular fibrillation or pulseless VT further.

Use of beta-blockers in atrial fibrillation

Atrial fibrillation is the most common arrhythmia in the general population and is frequently associated with organic heart disease. beta-adrenoceptor antagonists (b-blockers) are very effective in preventing atrial fibrillation after coronary artery bypass surgery. It has been shown recently that the beta-blocker metoprolol controlled release/extended release (CR/XL) is also effective in maintaining sinus rhythm after conversion of atrial fibrillation. There is concern that class I antiarrhythmic drugs, such as quinidine, disopyramide, and flecainide in particular, may increase mortality. The risk of proarrhythmia associated with beta-blocker treatment is very low. Therefore b-blockers, such as metoprolol CR/XL, may be the first line of treatment to maintain sinus rhythm, especially after myocardial infarction and in patients with chronic heart failure and in those with arterial hypertension. In patients with persistent atrial fibrillation, AV-nodal conduction-slowing drugs, such as calcium channel antagonists and beta-blockers are used to control the ventricular rate during atrial fibrillation. Several studies clearly show that beta-blockers alone, or in combination with digoxin are very effective in controlling the ventricular rate at rest and during exercise. beta-blockers are effective in maintaining sinus rhythm and controlling the ventricular rate during atrial fibrillation. Given these effects and their favorable effects on mortality, beta-blockers should be considered as first-line agents in the management of patients with atrial fibrillation.

Use of metoprolol CR/XL to maintain sinus rhythm after conversion from persistent atrial fibrillation: a randomized, double-blind, placebo-controlled study

OBJECTIVES

The primary objective of the present study was to assess the efficacy of metoprolol CR/XL to reduce the risk of relapse after cardioversion of persistent atrial fibrillation to sinus rhythm.

BACKGROUND

Indirect data from studies with d,l sotalol provide evidence that the beta-blocking effects of the compound are important in maintaining sinus rhythm after cardioversion of atrial fibrillation.

METHODS

After successful conversion to sinus rhythm, 394 patients with a history of persistent atrial fibrillation were randomly assigned to treatment with metoprolol CR/XL or placebo. The two treatment groups were similar with respect to all pretreatment characteristics. Patients were seen on an outpatient basis for recording of resting electrocardiogram (ECG) after one week, one, three and six months of follow-up or whenever they felt that they had a relapse into atrial fibrillation or experienced an adverse event.

RESULTS

In the metoprolol CR/XL group, 96 patients (48.7%) had a relapse into atrial fibrillation compared with 118 patients (59.9%) in the placebo group (p = 0.005). Heart rate in patients after a relapse into atrial fibrillation was significantly lower in the metoprolol group (98 +/- 23 beats/min) than in the placebo group (107 +/- 27 beats/min). The rate of adverse events reported was similar in both groups when the difference in follow-up time was taken into account.

CONCLUSIONS

The results of this double-blind, placebo-controlled study in patients after cardioversion of persistent atrial fibrillation showed that metoprolol CR/XL was effective in preventing relapse into atrial fibrillation or flutter.

Sotalol: An important new antiarrhythmic

Sotalol, the most recently approved oral antiarrhythmic drug, has a unique pharmacologic profile. Its electrophysiology is explained by nonselective beta-blocking action as well as class III antiarrhythmic activity (including fast-activating cardiac membrane-delayed rectifier current blockade), which leads to increases in action potential duration and refractory period throughout the heart and in QT interval on the surface electrocardiogram. Its better hemodynamic tolerance than other beta-blockers may be a result of enhanced inotropy associated with class III activity. Sotalol's ability to suppress ventricular ectopy is similar to that of class I agents and better than that of standard beta-blockers. Unlike class I agents, its use in a postinfarction trial was not associated with increased mortality rate. Therapeutically, it has shown superior efficacy for prevention of recurrent ventricular tachycardia and ventricular fibrillation, which was the basis for its approval. In a randomized study, the Electrophysiologic Study Versus Electrocardiographic Monitoring (ESVEM) trial, sotalol was associated with an increased in-hospital efficacy prediction rate (by Holter monitor or electrophysiologic study), reduced long-term arrhythmic recurrence rate with superior tolerance, and lower mortality rate than class I ("standard") antiarrhythmic drugs. Sotalol was 1 of 2 drugs selected for comparison with implantable defibrillators in the recent National Institutes of Health Antiarrhythmics versus Implantable Defibrillator (AVID) study. Sotalol appears to be a preferred drug for use with implantable defibrillators; unlike some other agents (eg, amiodarone) it does not elevate and, indeed, may lower defibrillation threshold. Although unapproved for this use, sotalol is active against atrial arrhythmias. It has shown efficacy equivalent to propafenone and quinidine in preventing atrial fibrillation recurrence, but it is better tolerated than quinidine and provides excellent rate control during recurrence. Sotalol's major side effects are related to beta-blockade and the risk of torsades de pointes (acceptably small if appropriate precautions are taken). Unlike several other antiarrhythmics (eg, amiodarone), it has no pharmacokinetic drug-drug interactions, is not metabolized, and is entirely renally excreted. Initial dose is 80 mg twice daily, with gradual titration to 240 to 360 mg/day as needed. The daily dose must be reduced in renal failure. On the basis of favorable clinical trials and practice experience, sotalol has shown a steadily growing impact on the treatment of arrhythmias during its 5 years of market availability, a trend that is likely to continue.

Comparison of metoprolol and sotalol in preventing ventricular tachyarrhythmias after the implantation of a cardioverter/defibrillator

The purpose of this prospective study was to evaluate, on an intention-to-treat basis, the efficacy of d,l-sotalol and metoprolol with regards to the recurrence of arrhythmic events after implantable cardioverter defibrillator (ICD) implantation. After ICD implantation, 70 patients were randomly assigned to treatment with either metoprolol (mean dosage 104+/-37 mg/day in 35 patients) or d,l-sotalol (mean dosage 242+/-109 mg/day in 35 patients). During follow up ventricular tachycardia (VT), fast VT, and ventricular fibrillation (VF) episodes were calculated. Metoprolol treatment led to a marked reduction in the recurrence of arrhythmic events. Actuarial rates for absence of VT recurrence at 1 and 2 years were significantly higher in the metoprolol group compared with the d,l-sotalol group (83% and 80% vs 57% and 51%, respectively, p=0.016). The actuarial rates for absence of fast VT or VF were 80% in the metoprolol group compared with 46% in the d,l-sotalol group (p=0.002). During a follow up of 26+/-16 months, there were 3 deaths in the metoprolol group compared with 6 deaths in the d,l-sotalol group. Actuarial rates of overall survival were not significantly different in the 2 groups (91% vs 83%, p=0.287). In this prospective, randomized, controlled study the recurrence rate of ventricular tachyarrhythmias in patients treated with metoprolol was lower than in patients treated by d,l-sotolol.

Drug-related torsades de pointes in the isolated rabbit heart: comparison of clofilium, d,l-sotalol, and erythromycin

Torsades de pointes is a potentially life-threatening form of polymorphic ventricular tachyarrhythmia typically seen in the presence of repolarization-prolonging agents. We investigated this particular form of tachyarrhythmia in the isolated, perfused rabbit heart. The experimental model was designed to reproduce conditions that are clinically known to be associated with an increased propensity to the development of torsades de pointes. The class III agent clofilium (1 microM) and d,l-sotalol (10 microM), as well as the antibiotic erythromycin (30-150 microM) were infused in the presence of either normal (5.88 mM) or low (1.5 mM) potassium concentration in sinus-driven or atrioventricular (AV)-blocked hearts. Ventricular tachyarrhythmias spontaneously emerged in the clofilium-, d,l-sotalol-, and erythromycin-treated AV-blocked hearts. The episodes showed typical features of torsades de pointes found in humans. They developed within 4-12 min after the onset of infusion, were normally nonsustained, and only rarely degenerated into ventricular fibrillation. Electrical stimulation at cycle lengths <600 ms and perfusion with MgSO4 suppressed arrhythmic activity. In the d,l-sotalol- and erythromycin-treated hearts, torsades de pointes occurred only in the presence of hypokalemia and bradycardia, whereas, in the presence of clofilium, bradycardia alone caused torsades de pointes. Monophasic action-potential recordings demonstrated early afterdepolarizations in endocardial and epicardial recordings. Thus the isolated AV-blocked rabbit heart represents a model for studying drug-related torsades de pointes and its mechanism.

Comparison of sotalol and metoprolol in the prevention of atrial fibrillation after coronary artery bypass surgery

New-onset atrial fibrillation (AF) is frequent after coronary artery bypass grafting (CABG), and beta-blockers decrease its incidence. To examine whether a beta-blocker with class III properties is superior to a pure one, 191 consecutive patients undergoing CABG were randomized to receive oral sotalol, 120 mg daily (n = 93), or metoprolol, 75 mg daily (n = 98), postoperatively. The doses were adjusted if beta-blockade was inadequate or excessive. AF occurred in 16 (16%) of 98 sotalol patients and in 30 (32%) of 93 metoprolol patients (p < 0.01). Symptoms related to beta-blockade or proarrhythmia did not appear. After CABG, sinus heart rate increased in both groups (p < 0.001) but less in the sotalol patients (p < 0.001) throughout the postoperative period. Corrected QT duration (by the Bazett equation) was prolonged after the operation in both groups (p < 0.001), whereas uncorrected QT duration at similar heart-rate levels were prolonged only in sotalol patients (mean increase, 31 ms; 95% confidence interval, 2042 ms; p < 0.01). Uncorrected QT durations at similar heart-rate levels were longer during sotalol (compared with metoprolol) treatment (p < 0.05). Heart rates or QT durations did not differ between the patients with or without AF. In conclusion, sotalol significantly reduces the incidence of AF after CABG. Although a marked class III effect is demonstrated with relatively low doses (as prolonged ventricular repolarization) in direct comparison unbiased by any rate correction, its contribution as an enhanced antifibrillatory mechanism in the postoperative state remains unconfirmed.

Electrophysiologic features of torsades de pointes: insights from a new isolated rabbit heart model

INTRODUCTION

The exact electrophysiologic mechanism of torsades de pointes (TdP) is under intense investigation. No isolated animal heart model of this particular arrhythmia exists.

METHODS AND RESULTS

In isolated rabbit hearts, TdP was induced by means of bradycardia in the presence of a high concentration of d-sotalol (10(-4) M) and shortly after lowering the concentration of potassium and magnesium in the perfusate. Multiple simultaneous epicardial and endocardial monophasic action potentials (MAPs) and volume-conducted 12-lead ECGs were recorded. d-Sotalol prolonged repolarization and increased dispersion of ventricular repolarization compared to baseline recordings. With the onset of low potassium and magnesium concentrations, repolarization was further prolonged and dispersion of repolarization was further increased followed by the occurrence of early afterdepolarizations (EADs) in the majority of MAP recordings, i.e., at both endocardial and epicardial locations of both ventricles. Upon increase of EAD amplitude, triggered arrhythmias with TdP of up to 42 beats ensued in 10 of 11 hearts studied. MAP duration at 90% repolarization (APD90), dispersion of APD90, and the incidence of EADs as well as dispersion of the QT interval and T wave area were significantly higher in beats triggering bigemini, couplets, or runs of TdP.

CONCLUSION

TdP observed in this new isolated heart model was associated with markedly increased dispersion of ventricular repolarization and the occurrence of EADs in multiple locations of the heart. TdP is initiated when the amplitude of an EAD reaches threshold for initiation of the first beat of an episode.

Circadian variation of sustained ventricular tachycardia in patients subject to standard adrenergic blockade

Morning peaks in the circadian variation of sustained ventricular tachycardia (VT) may reflect the contribution of sympathetic activation to onset of VT. We hypothesized that adrenergic blockade would eliminate this morning peak. Fifty-four patients using a defibrillator had 1114 time-stamped episodes of VT requiring therapy with a device: 1012 episodes with and 102 episodes without antiadrenergic medications. Nine patients had episodes both with and without antiadrenergic medication and were examined separately. In patients taking antiadrenergic agents, data fitted to a harmonic regression model revealed a morning peak at 9:00 AM (R2= 0.542; p < 0.05), with a secondary peak at 4 PM. Those not receiving antiadrenergic therapy had a similar morning peak. Antiadrenergic agents as used in standard clinical practice do not prevent circadian variation in onset of VT. This variation may be mediated by systems other than adrenergic receptor-linked activation or may reflect inadequacy of adrenergic blockade in standard clinical dosing.

Electrophysiologic mechanisms of antiarrhythmic efficacy of a sotalol and class Ia drug combination: elimination of reverse use dependence

OBJECTIVES

We sought to determine the electrophysiologic mechanisms explaining the efficacy of combination therapy with DL-sotalol and a type Ia drug in the treatment of ventricular tachycardia (VT).

BACKGROUND

Combination antiarrhythmic drug therapy with low dose DL-sotalol plus a type Ia antiarrhythmic agent has been shown to prevent spontaneous and induced VT. The mechanisms underlying the efficacy of this drug combination have not been fully elucidated.

METHODS

We studied 32 patients with spontaneous sustained VT by using programmed electrical stimulation in the drug-free condition and after treatment with DL-sotalol (average dose [mean +/- SE] 151 +/- 8 mg/day) and a class Ia agent (quinidine, 1,337 +/- 59 mg/day, or procainamide, 2,083 +/- 327 mg/day). Sustained VT was induced in all patients at baseline study, and induction was reattempted during drug therapy. Monophasic action potential duration at 90% repolarization (APD90) and ventricular effective refractory period (ERP) were recorded with use of a contact electrode.

RESULTS

Ventricular ERP increased from 258 +/- 4 ms at baseline to 310 +/- 6 ms at a 600-ms drive cycle length (DCL600) with treatment (p < 0.001). APD90 increased from 288 +/- 6 ms by +10.1% at DCL600 and from 267 +/- 7 ms by +13.3% at a 400-ms drive cycle length (DCL400) (p < 0.001). Paced QRS duration increased from 141 +/- 3 to 158 +/- 6 ms at DCL400 (p < 0.05). At baseline, the shortest achieved coupling interval between successive propagated extrastimuli decreased progressively with respect to the first extrastimulus, following double and triple extrastimuli, at both DCL600 (-14.0% and -20.0%, respectively) and at DCL400 (-16.4% and -22.4%, respectively). This "peeling back" of refractoriness was attenuated on therapy with sotalol plus a class Ia antiarrhythmic agent to -6.7% and -10.5% (DCL600, p < 0.05), and -8.1%, -9.5% (DCL400, p < 0.05), for double and triple extrastimuli, respectively. The absolute prolongation of functional refractory periods by the drug combination increased with successive extrastimuli, from 55 +/- 6 ms for the V1V2 interval to 75 +/- 6 ms for V2V3 and 67 +/- 6 ms for V3V4 at DCL600, and from 51 +/- 5 ms for V1V2 to 69 +/- 6 ms for V2V3 and 74 +/- 7 ms for V3V4 at DCL400 (p < 0.001).

CONCLUSIONS

The combination of low dose sotalol and a class Ia agent greatly prolongs refractoriness. The magnitude of the effect increases at shorter coupling intervals.

Mexiletine antagonizes effects of sotalol on QT interval duration and its proarrhythmic effects in a canine model of torsade de pointes

OBJECTIVES

The arrhythmogenic and electrophysiologic properties of sotalol, a class III antiarrhythmic drug, administered alone and in combination with mexiletine, a class I antiarrhythmic drug, were compared in conscious dogs predisposed to torsade de pointes arrhythmias.

BACKGROUND

The utility of sotalol is limited by proarrhythmia related to excessive delays in repolarization. The addition of mexiletine may limit the risk of torsade de pointes because it reduced in vitro the sotalol-induced increase in action potential duration.

METHODS

Two studies were performed in eight hypokalemic dogs (plasma potassium level < or = 3.2 mmol/liter) with chronic atrioventricular block (mean ventricular cycle length, RR 1,100 ms) at 3-day intervals using a crossover protocol. Intravenous sotalol (4.5 + 1.5 mg/kg body weight per h) alone was given for 2 h, or, on another day, an intravenous mexiletine infusion (4.5 + 1.5 mg/kg per h) was begun 30 min before sotalol infusion. Spontaneous ventricular cycle length and QT interval and ventricular effective refractory period at the 1,000-ms pacing cycle length were measured at baseline and 30 min after the onset of each drug infusion. The electrocardiogram (ECG) was continuously monitored for torsade de pointes.

RESULTS

Sotalol plus mexiletine and sotalol alone had a significant (p < or = 0.05) and similar effect on ventricular cycle length (+ 800 +/- 93 vs. + 690 +/- 104 ms [mean +/- SEM]) and ventricular effective refractory period (+ 20 +/- 4 vs. + 25 +/- 4 ms), but sotalol plus mexiletine had a lesser effect on QT interval (+ 20 +/- 6 vs. + 50 +/- 8 ms, p < or = 0.05). Torsade de pointes is less frequent (one of eight dogs vs. six of eight dogs, p = 0.02) with sotalol plus mexiletine than with sotalol alone.

CONCLUSIONS

The coadministration of a class Ib agent can reduce the proarrhythmic potential of a class III drug in experimental animals predisposed to torsade de pointes arrhythmias and further suggests the clinical utility of such a strategy.

Sotalol: a new beta-adrenergic blocker for ventricular arrhythmias

Sotalol is a water-soluble, nonselective, beta-adrenergic blocker that was recently approved in oral form in the United States for the treatment of ventricular arrhythmias that are judged to be life-threatening. As a beta-blocker, sotalol is unique in having additional class-III antiarrhythmic activity. It is still not resolved whether sotalol is more effective than other beta-blockers in managing arrhythmias, but there are suggestions that it might possess greater antiarrhythmic and life-protecting activities than other types of antiarrhythmic drugs. The drug is well tolerated, but, because of its electrophysiologic activity, there is a small risk of proarrhythmia, specifically the development of polymorphic ventricular tachycardia and torsade de pointes.

Class III antiarrhythmic drug action in experimental atrial fibrillation. Differences in reverse use dependence and effectiveness between d-sotalol and the new antiarrhythmic drug ambasilide

BACKGROUND

Drug therapy to maintain sinus rhythm in patients with atrial fibrillation (AF) is limited by adverse effects and inadequate efficacy. There has been an increased interest in the use of class III drugs to treat AF, and several new agents have been developed, but there is little information available about mechanisms of class III drug action in AF. The present study was designed to compare the effects of two class III agents, d-sotalol and ambasilide, in dog models of experimental AF.

METHODS AND RESULTS

A previously developed dog model of sustained vagotonic AF was used to assess the ability of equal loading doses of d-sotalol and ambasilide (2 mg/kg, followed by maintenance infusions), to terminate AF and prevent its induction. At this dose, ambasilide terminated AF in 12 of 12 dogs and prevented AF induction in 10 of 12 dogs; d-sotalol terminated AF in 1 of 8 dogs (P = .001 versus ambasilide) and prevented AF induction in none of 8 dogs (P = .002). An additional dose of d-sotalol (cumulative load, 8 mg/kg) terminated AF in 7 of 8 dogs and prevented induction in 5 of 8 dogs. In an additional 6 dogs with sterile pericarditis and inducible AF, ambasilide prevented AF induction in all 6. An equal dose of d-sotalol (2 mg/kg) failed to suppress AF induction in any dog, but 8 mg/kg of d-sotalol suppressed AF induction in all. Atrial effective refractory period (AERP) was increased by both drugs. However, the effects of d-sotalol on AERP showed strong reverse use dependence, whereas those of ambasilide did not. Neither ambasilide nor d-sotalol significantly altered conduction velocity, and both increased ventricular refractoriness, with d-sotalol once again showing more reverse use dependence. Effective doses of both agents increased AERP and the wavelength for atrial reentry at rapid rates, slowing atrial activation and terminating the arrhythmia.

CONCLUSIONS

The class III drugs d-sotalol and ambasilide terminate AF by increasing AERP and the wavelength for reentry. Ambasilide, which has been reported to block both the rapid and slow components of the delayed rectifier (IKr and IKs), shows less reverse use dependence of effects on refractoriness than the pure IKr blocker d-sotalol, possibly explaining the greater effectiveness of ambasilide at an equal dose level. These results indicate that class III drugs can exhibit different profiles of rate-dependent action on AERP and suggest that it may be possible to develop agents that have more desirable rate-dependent profiles than pure blockers of Ikr.

Sotalol

Sotalol is a novel antiarrhythmic agent combining beta-adrenergic-antagonist actions with the ability to increase cardiac repolarization and refractoriness. The drug's electrophysiologic and clinical profile is different from that of conventional beta-receptor antagonists. As compared with other antiarrhythmic agents, sotalol prevents recurrences of arrhythmia in a higher proportion of patients, particularly among those presenting with ventricular tachycardia and aborted sudden cardiac death. The net hemodynamic effect of sotalol is the result of a balance between the depressant effects due to beta-receptor blockade and an action that tends to increase contractility. Although initially marketed in the United States for treatment of life-threatening ventricular arrhythmias, sotalol also has demonstrated efficacy in many patients with supraventricular arrhythmias. As with all drugs that prolong the QT interval, the syndrome of torsade de pointes is a serious potential adverse effect.

Sotalol. An updated review of its pharmacological properties and therapeutic use in cardiac arrhythmias

Sotalol is a nonselective beta-adrenoceptor antagonist which prolongs cardiac repolarisation independently of its antiadrenergic action (class III antiarrhythmic properties). The antiarrhythmic action of sotalol appears to arise predominantly from its class III properties, and the drug exhibits a broader antiarrhythmic profile than the conventional beta-blockers. Sotalol is effective in controlling paroxysmal supraventricular tachycardias and the ventricular response to atrial fibrillation/flutter in Wolff-Parkinson-White syndrome, in maintaining sinus rhythm after cardioversion of atrial fibrillation/flutter, and in preventing initiation of supraventricular tachyarrhythmias following coronary artery bypass surgery. Sotalol shows promise in the control of nonmalignant and life-threatening ventricular arrhythmias, particularly those associated with ischaemic heart disease. It is effective in suppressing complex forms of ventricular ectopy, displaying superior antiectopic activity to propranolol and metoprolol. The acute efficacy of sotalol in preventing reinduction of sustained ventricular tachyarrhythmias and suppressing spontaneous episodes of these arrhythmias on Holter monitoring is translated into long term prophylactic efficacy against arrhythmia recurrence in approximately 55 to 85% of patients with refractory life-threatening ventricular arrhythmias. In addition, sotalol offers the advantage over the class I agents of reducing cardiac and all-cause mortality in the high risk population with life-threatening ventricular arrhythmias. The adverse effects of sotalol are primarily related to its beta-blocking activity and its class III property of prolonging cardiac repolarisation. Sotalol is devoid of overt cardiodepressant activity in patients with mild or moderate left ventricular dysfunction. The overall arrhythmogenic potential is moderately low, but torsade de pointes may develop in conjunction with excessive prolongation of the QT interval due to bradycardia, hypokalaemia or high plasma concentrations of the drug. In summary, sotalol displays a broad spectrum of antiarrhythmic activity, is haemodynamically well tolerated, and confers a relatively low proarrhythmic risk. It is likely to prove particularly appropriate in the treatment and prophylaxis of life-threatening ventricular tachyarrhythmias.

Comparative mechanisms of antiarrhythmic drug action in experimental atrial fibrillation. Importance of use-dependent effects on refractoriness

BACKGROUND

Antiarrhythmic drugs are considered to terminate atrial fibrillation by prolonging refractoriness, but direct experimental evaluation of this concept has been limited. The atria are activated rapidly during atrial fibrillation, and antiarrhythmic drugs are known to have important rate-dependent actions. The potential role of such properties in determining drug effects during atrial fibrillation has not been evaluated.

METHODS AND RESULTS

We evaluated the effects of representative class Ia (procainamide), Ic (propafenone), and III (sotalol) antiarrhythmic drugs on sustained cholinergic atrial fibrillation and atrial electrophysiological properties in anesthetized, open-chest dogs. Loading and maintenance doses were used to produce stable plasma concentrations, and computer-based 112-electrode epicardial mapping was used to study atrial conduction and activation during atrial fibrillation. Clinically used doses of procainamide and propafenone terminated atrial fibrillation in 13 of 13 (100%) and 7 of 10 (70%) dogs, respectively, but a dose of sotalol (2 mg/kg IV) in the clinical range terminated atrial fibrillation in only 2 of 8 (25%) dogs (P = .0005 vs procainamide, P = .08 vs propafenone). Procainamide and propafenone prevented atrial fibrillation induction in 13 of 13 (100%) and 7 of 10 (70%) dogs, respectively, compared with none of 8 dogs for 2 mg/kg sotalol (P < .0001 vs procainamide, P = .004 vs propafenone). A larger dose of sotalol (cumulative dose, 8 mg/kg) was uniformly effective in terminating atrial fibrillation and preventing its induction. All drugs significantly increased atrial refractory period, with effects that were use dependent for propafenone but reverse use dependent for sotalol. Effective doses of all drugs significantly increased the wavelength for reentry at rapid atrial rates in the presence of vagal stimulation into the range observed under drug-free conditions in the absence of vagal input. The inefficacy of clinical doses of sotalol was explained by the reverse use dependence of its effects on refractoriness, which resulted in reduced effects on wavelength at rapid rates. The effects of propafenone on refractoriness were significantly increased at rapid rates, contributing to its ability to increase wavelength and terminate atrial fibrillation. Activation mapping showed that drugs terminated atrial fibrillation by reducing the number and increasing the size of reentry circuits, leading to termination by mechanisms related to block in the remaining circuit(s).

CONCLUSIONS

We conclude that antiarrhythmic drugs terminate experimental atrial fibrillation by increasing the wavelength for reentry at rapid rates, leading to a reduction in the number of functional reentry circuits and, eventually, failure of reentrant excitation. Use-dependent effects on refractoriness can limit (in the case of the reverse use dependence of sotalol) or contribute (in the case of propafenone) to antiarrhythmic drug efficacy against atrial fibrillation by determining drug-induced changes in wavelength at rapid atrial rates.

Pharmacologic basis of the antiarrhythmic and hemodynamic effects of sotalol

Sotalol is a competitive beta adrenoceptor antagonist devoid of membrane-stabilizing activity and intrinsic sympathomimetic activity that has no preferential actions on beta 1 or beta 2 responses. No other tested receptor systems are affected by sotalol. In addition to having class II (beta blockade) effects, sotalol also has class III antiarrhythmic activity. It increases the action potential duration (APD) and prolongs atrial and ventricular repolarization. The effect on APD is independent of beta blockade; the same effect is seen with similar concentrations of the d stereoisomer of sotalol, which does not have beta-blocking activity. Sotalol prolongs the rate-corrected QT interval and ventricular and atrial refractoriness without affecting atrial, His-Purkinje, or ventricular conduction velocity. Atrioventricular nodal conduction is decreased, largely because of beta blockade. Sotalol increases the fibrillation threshold and decreases the defibrillation threshold. Sotalol is an effective antiarrhythmic in various animal models of arrhythmia (e.g., chloroform, hydrocarbon-catecholamine, ouabain, and coronary ligation). In addition, it reduces the severity and frequency of arrhythmias induced by programmed electrical simulation. By comparison, metoprolol is ineffective and d-sotalol is as effective as the racemate in this model, indicating that this effect is independent of beta blockade. Sotalol causes concentration-dependent increases in the contractility of isolated ventricular tissue that is not blocked by previous beta or alpha blockade or catecholamine depletion. The positive inotropic effect may be related to inhibition of time-dependent K+ current responsible for the increase in APD. Like propranolol, sotalol decreases contractile force, heart rate, arterial blood pressure, left ventricular dP/dt, and cardiac output in intact animals due to blockade of circulating catecholamines. Sotalol consistently reduces the heart rate to a greater degree than propranolol and causes significantly less cardiac suppression than propranolol at a given heart rate.

Sotalol

Sotalol causes noncardioselective beta-adrenergic antagonism and prolongation of repolarization of cardiac tissues (Class III electrophysiologic action). This dual pharmacologic profile confers unprecedented antiarrhythmic properties to the drug. Sotalol is highly bioavailable when administered orally in the fasting state and is mostly cleared unchanged in the urine with an apparent half-life of elimination of 15 to 17 hours. It has been found effective in the suppression of nearly all cardiac arrhythmias, with the exception of those precipitated by prolongation of ventricular repolarization. Its safety and efficacy relative to other antiarrhythmic drugs need to be examined more fully in randomized controlled trials of unselected patients. The adverse effects potentially associated with the use of sotalol are those commonly observed with beta-adrenergic blockade, as well as those resulting from excessive prolongation of the QT interval. The occurrence of torsade de pointes during treatment with sotalol may be minimized by limiting doses to no more than 640 mg/day and by strictly avoiding the development of hypokalemia.

Efficacy of antiarrhythmic drugs in patients with arrhythmogenic right ventricular disease. Results in patients with inducible and noninducible ventricular tachycardia

BACKGROUND

Ventricular tachyarrhythmias are the major clinical manifestation of arrhythmogenic right ventricular disease. Although antiarrhythmic therapy has been widely advocated, there is only limited information available on the efficacy of antiarrhythmic drugs in these patients.

METHODS AND RESULTS

The short- and long-term efficacies of various antiarrhythmic agents were retrospectively and prospectively analyzed in 81 patients (mean age, 39 +/- 14 years; range, 16-68 years; 61.7% males) with arrhythmogenic right ventricular disease. In 42 patients with inducible ventricular tachycardia during programmed ventricular stimulation, the following efficacy rates were obtained: class Ia and Ib drugs (n = 18), 5.6%; class Ic drugs (n = 25), 12%; beta-blockers (n = 8), 0%; sotalol (n = 38), 68.4%; amiodarone (n = 13), 15.4%; verapamil (n = 5), 0%; and drug combinations (n = 26), 15.4%. Only one of the 10 patients not responding to sotalol was treated effectively by amiodarone, whereas the remaining nine patients proved to be drug refractory toward all other drugs tested (3.8 +/- 2.3 drugs, including amiodarone in five cases) and underwent nonpharmacological therapy. During a follow-up of 34 +/- 25 months, three of the 31 patients (9.7%) discharged on pharmacological therapy had nonfatal recurrences of ventricular tachycardia after 0.5, 51, and 63 months, respectively. In 39 patients with noninducible ventricular tachycardia during programmed ventricular stimulation, the following efficacy rates were observed: class Ia and Ib drugs (n = 16), 0%; class Ic agents (n = 23), 17.4%; beta-blockers (n = 7), 28.6%; sotalol (n = 35), 82.8%; amiodarone (n = 4), 25%; verapamil (n = 24), 50%; and drug combinations (n = 11), 9.1%. During a follow-up of 14 +/- 13 months, four of 33 patients (12.1%) discharged on antiarrhythmic drugs had nonfatal relapses of their clinical ventricular arrhythmia.

CONCLUSIONS

Thus, in arrhythmogenic right ventricular disease, sotalol proved to be highly effective in patients with inducible as well as noninducible ventricular tachycardia. Patients with inducible ventricular tachycardia not responding to sotalol are likely to not respond to other antiarrhythmic drugs and should be considered for nonpharmacological therapy without further drug testing. Amiodarone did not prove to be more effective than sotalol and may not be an alternative because of frequent side effects during long-term therapy, especially in young patients. Verapamil and beta-blockers were effective in a considerable number of patients with noninducible ventricular tachycardia and may be a therapeutic alternative in this subgroup. Class I agents appear to be rarely effective in the treatment of both inducible and noninducible ventricular tachycardia in arrhythmogenic right ventricular disease.

Rate dependence of sotalol-induced prolongation of ventricular repolarization during exercise in humans

Studies in animals have shown that drug-induced action potential prolongation with class III antiarrhythmic agents increases with slow pacing rates. We studied the physiological rate dependence of sotalol effects on ventricular repolarization, measured as QT interval duration on the surface electrocardiogram at rest and during a maximal exercise test, in 10 normal volunteers. In a randomized, crossover study, three dosages of sotalol (160 mg/24 hr, 320 mg/24 hr, and 640 mg/24 hr) were administered during 4 days to each subject. In a control period, no drug was administered. During each period, 50-100 QT intervals were measured over a wide range of RR intervals recorded at rest and during the course of a maximal exercise test. Plasma sotalol concentration and beta-adrenoceptor blockade (percent reduction in peak exercise heart rate from control) were also measured. The QT-versus-RR relation was fitted to several formulas, and the overall best fit was used to calculate QT interval duration normalized for a heart rate of 60 beats/min (QTc) and to analyze the rate dependence of QT prolongation with sotalol. Sotalol-induced beta-adrenoceptor blockade and QTc prolongation were dose and concentration dependent. Sotalol reduced peak exercise heart rate by 13.8 +/- 7% at the dosage of 320 mg/24 hr and by 25.4 +/- 8% at the dosage of 640 mg/24 hr (both p less than 0.01). Sotalol prolonged QTc interval by 5.8 +/- 3.7% and 11.8 +/- 3% at these respective dosages (both p less than 0.01). The concentration of sotalol required to produce minimal (mean QTc prolongation, 5.6%; confidence interval, 0-11.2%) QTc prolongation (680 ng/ml) tended to be lower than that required for minimal (mean percent reduction in maximal exercise heart rate, 13.9%; confidence interval, 0-27.8%) beta-blockade (840 ng/ml). QT prolongation with sotalol increased with increasing RR intervals (i.e., decreasing heart rate) at all dosages. QT prolongation became statistically significant for RR of 800 msec or more at all dosages and for RR intervals of 600 msec or more at the dosage of 640 mg/24 hr. This rate dependence altered the relation between QT interval duration and sotalol plasma concentrations. These results suggest that sotalol prolongs QTc interval in humans at dosages and concentrations similar to those required to produce beta-adrenoceptor blockade, QT prolongation with sotalol is more pronounced when heart rate decreases and is not apparent during exercise-induced tachycardia, and the relation between QT prolongation with sotalol and plasma concentrations of the drug depends on the heart rate at which measurements are made.

Sotalol in patients with life-threatening ventricular tachyarrhythmias

To assess the antiarrhythmic efficacy of oral d,l-sotalol, 68 patients with sustained monomorphic ventricular tachycardia (SMVT) (n = 62) or ventricular fibrillation (VF) (n = 6) were studied by programmed ventricular stimulation (PVS). Fifty-one patients had coronary artery disease with a previous myocardial infarction and there were 17 patients without coronary disease: 11 patients had right and/or left ventricular dysplasia, one patient an aortic-valve replacement, and five patients had no visible heart disease. Prior to sotalol patients were treated with a mean of 3.6 +/- 1.3 antiarrhythmic class I drugs. None of these drugs prevented SMVT or VF. During control PVS (PVS 1), VF was induced in 8 patients (12%), SMVT in 47 patients (69%), and nonsustained ventricular tachycardia (NSVT) in 13 patients (19%). After loading with oral d,l-sotalol (320 mg/day), PVS (PVS 2) was repeated 4.2 +/- 3.3 weeks after PVS 1. In one of the patients (1%) VF was inducible, in 15 patients (22%) SMVT was induced, and in 18 patients (26%) NSVT was induced. In 34 patients (50%) either no or a short ventricular response was inducible. Our data show that oral d,l-sotalol is an effective antiarrhythmic agent in patients with SMVT or VF.

A mechanism of D-(+)-sotalol effects on heart rate not related to beta-adrenoceptor antagonism

1. In order to determine whether the effects of d- or (+)-sotalol on heart rate are mediated by beta-adrenoceptor antagonism or might be due to other actions, we administered (+)-sotalol (400 mg every 12 h), atenolol (50 mg every 12 h) and placebo to eight healthy volunteers in a randomized, double-blind, crossover study. We also studied the affinity of human lymphocyte beta 2-adrenoceptor for (+)-sotalol, (-)-sotalol, and (+/-)-propranolol. 2. Compared with placebo, atenolol significantly reduced resting, standing and peak exercise heart rate whereas (+)-sotalol significantly reduced standing and peak exercise heart rate, but not resting heart rate. Atenolol significantly reduced resting, standing and peak exercise blood pressure while (+)-sotalol had no effect. 3. (+)-sotalol and atenolol both shifted the relationship between isoprenaline dose and heart rate to the right by similar degrees at the dosages tested. 4. (+)-sotalol but not atenolol significantly prolonged QTc interval. The degree of QTc prolongation due to (+)-sotalol, which has been shown to parallel action potential prolongation in the sinus node, correlated significantly with the reduction in peak exercise. heart rate it produced (r = 0.71, n = 8, P less than 0.05). 5. The affinity of the human lymphocyte beta 2-adrenoceptor was approximately 60-fold greater for (-)-sotalol (Ki, 108 +/- 12 nM) than for (+)-sotalol (Ki, 6,410 +/- 1,020 nM), and approximately 20,000-fold greater for (+/-)-propranolol (Ki, 0.33 +/- 0.08 nM) than for (+)-sotalol.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of flecainide and quinidine on human atrial action potentials. Role of rate-dependence and comparison with guinea pig, rabbit, and dog tissues

Flecainide and other class IC antiarrhythmic drugs are effective in the prevention and termination of atrial fibrillation, but the mechanism of this action is unknown. To gain insights into potential cellular mechanisms, we evaluated the response of human atrial action potentials to equimolar therapeutic concentrations of flecainide and quinidine and compared this response to that of guinea pig, rabbit, and dog atria. Both compounds reduced Vmax more as activation rate increased, but flecainide was more potent than quinidine and had slower kinetics. The rate-dependence of Vmax reduction was similar for all species, but human tissue was more sensitive to the drugs tested. In contrast to changes in Vmax, drug-induced alterations in action potential duration showed opposite rate-dependence for the two drugs. Quinidine increased action potential duration to 95% repolarization (APD95) in human atria by 33 +/- 7% (mean +/- SD) at a cycle length of 1,000 msec, but this effect was reduced as cycle length decreased, to 12 +/- 4% (p less than 0.001) at a cycle length of 300 msec. Flecainide increased APD95 (by 6 +/- 3%) much less than quinidine at a cycle length of 1,000 msec, but its effect was increased by faster pacing, to 27 +/- 12% at a cycle length of 300 msec and 35 +/- 8% (p less than 0.001) at the shortest 1:1 cycle length. The rate-dependent response of APD to drugs was qualitatively similar but quantitatively different among species. Human tissue showed the greatest frequency-dependent drug effects on repolarization, followed by tissue from dogs and rabbits. Guinea pig atria showed the least (and statistically nonsignificant) rate-dependence of drug effect on APD. Drug-induced changes in refractoriness paralleled those in APD. We conclude that: 1) flecainide and quinidine both increase APD in human atrial tissue but with opposite rate-dependence, 2) the effects of flecainide to increase atrial APD and refractoriness are enhanced by the rapid rates typical of atrial fibrillation, and 3) animal tissues may differ importantly from human in both their sensitivity and rate-dependent response to antiarrhythmic drugs. The salutary response of atrial fibrillation to flecainide may be due to enhancement of drug action by the rapid atrial activation rates characteristic of this arrhythmia.

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)