Arrhythmia and acute coronary syndrome suppression and cardiac resuscitation management with bretylium.

It is well known that electric shock can both initiate and terminate ventricular fibrillation. Refractory ventricular fibrillation (RVF) may often be an iatrogenic paradoxical result of early, frequent, excessive salvos of DC current countershocks and inappropriate off-label drug use, particularly aggressive epinephrine administration. Evidence suggests that the current advanced cardiac life support pharmacology protocol for cardiac resuscitation may contribute to disappointing survival in patients with out-of-hospital cardiac arrest. Controlled studies and new theoretical consideration suggest the protocol may induce RVF. In contrast, studies suggest that immediate adequate intravenous bretylium administration therapy together with sustained effective chest compressions can induce chemical defibrillation or facilitate electrical defibrillation as well as reduce the intensity, or even need for potentially heart-damaging countershock, where early frequent excessive current shocks are likely to increase refractory arrhythmia as demonstrated in animals and in humans. Salvos of shocks do not allow time between shocks for uniform recovery of normal electrical parameters needed to restore a stable heart rhythm. This may occur by inadvertently administering shock during the vulnerable period of the cardiac cycle. There are compelling existing data to demonstrate that bretylium and cardiopulmonary resuscitation (CPR) delivered before initiating shock therapy is likely to provide the best outcome in cardiac arrest. But, most importantly, adequate CPR chest compressions administered while bretylium is being infused also provide the opportunity to wash out electrically destabilizing electrolytes that have leaked from or are abnormally transported by functionally damaged membranes of fibrillation-induced ischemic myocytes. This may cause abnormal compartment redistribution of electrolytes that may facilitate RVF by heterogeneously partially depolarizing ischemic myocytes. Although efforts have been made to provide hard science for advanced life support, the guidelines are a product of consensus, the give and take of collegiality and intuition rather than rigorous controlled studies. Bretylium has a direct antifibrillatory action normalizing myocyte membrane currents, which restores intracompartmental normal electrolyte balance. In addition, adrenergic blockade by bretylium dilates coronary arteries, increasing effective O2 delivery by CPR. The free and aggressive use of epinephrine is toxic. Catechalomines cause coronary spasm and puts myocardial metabolism into damaging hypermetabolic overdrive to support the "fight or flight reflex" rapidly depleting adenosine triphosphate needed for cardiac electrical and mechanical recovery. Moreover, the value of epinephrine to resuscitation has never been demonstrated in a controlled human study, whereas its potential damage has been largely ignored. Epinephrine's potential deleterious actions that might compromise resuscitation are well established and reviewed here.

Influence of hyperoxia on skin vasomotor control in normothermic and heat-stressed humans.

Hyperoxia induces skin vasoconstriction in humans, but the mechanism is still unclear. In the present study we examined whether the vasoconstrictor response to hyperoxia is through activated adrenergic function (protocol 1) or through inhibitory effects on nitric oxide synthase (NOS) and/or cyclooxygenase (COX) (protocol 2). We also tested whether any such vasoconstrictor effect is altered by body heating. In protocol 1 (n = 11 male subjects), release of norepinephrine from adrenergic terminals in the forearm skin was blocked locally by iontophoresis of bretylium (BT). In protocol 2, the NOS inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME) and the nonselective COX antagonist ketorolac (Keto) were separately administered by intradermal microdialysis in 11 male subjects. In the two protocols, subjects breathed 21% (room air) or 100% O(2) in both normothermia and hyperthermia. Skin blood flow (SkBF) was monitored by laser-Doppler flowmetry. Cutaneous vascular conductance (CVC) was calculated as the ratio of SkBF to blood pressure measured by Finapres. In protocol 1, breathing 100% O(2) decreased (P < 0.05) CVC at the BT-treated and at untreated sites from the levels of CVC during 21% O(2) breathing both in normothermia and hyperthermia. In protocol 2, the administration of l-NAME inhibited (P < 0.05) the reduction of CVC during 100% O(2) breathing in both thermal conditions. The administration of Keto inhibited (P < 0.05) the reduction of CVC during 100% O(2) breathing in hyperthermia but not in normothermia. These results suggest that skin vasoconstriction with hyperoxia is partly due to the decreased activity of functional NOS in normothermia and hyperthermia. We found no significant role for adrenergic mechanisms in hyperoxic vasoconstriction. Decreased production of vasodilator prostaglandins may play a role in hyperoxia-induced cutaneous vasoconstriction in heat-stressed humans.

Prevention of ventricular fibrillation, acute myocardial infarction (myocardial necrosis), heart failure, and mortality by bretylium: is ischemic heart disease primarily adrenergic cardiovascular disease?

It is widely, but mistakenly, believed that ischemic heart disease (IsHD) and its complications are the sole and direct result of reduced coronary blood flow by obstructive coronary artery disease (CAD). However, cardiac angina, acute myocardial infarction (AMI), and sudden cardiac death (SCD) occur in 15%-20% of patients with anatomically unobstructed and grossly normal coronaries. Moreover, severe obstructive coronary disease often occurs without associated pathologic myocardiopathy or prior symptoms, ie, unexpected sudden death, silent myocardial infarction, or the insidious appearance of congestive heart failure (CHF). The fact that catecholamines explosively augment oxidative metabolism much more than cardiac work is generally underappreciated. Thus, adrenergic actions alone are likely to be more prone to cause cardiac ischemia than reduced coronary blood flow per se. The autonomic etiology of IsHD raises contradictions to the traditional concept of anatomically obstructive CAD as the lone cause of cardiac ischemia and AMI. Actually, all the signs and symptoms of IsHD reflect autonomic nervous system imbalance, particularly adrenergic hyperactivity, which may by itself cause ischemia as in rest angina. Adrenergic activity causing ischemia signals cardiac pain to pain centers via sympathetic efferent pathways and tend to induce arrhythmogenic and necrotizing ischemic actions on the cardiovascular system. This may result in ischemia induced metabolic myocardiopathy not unlike that caused by anatomic or spasmogenic coronary obstruction. The clinical study and review presented herein suggest that adrenergic hyperactivity alone without CAD can be a primary cause of IsHD. Thus, adrenergic heart disease (AdHD), or actually adrenergic cardiovascular heart disease (ACVHD), appears to be a distinct entity, most commonly but not necessarily occurring in parallel with CAD. CAD certainly contributes to vulnerability as well as the progression of IsHD. This vicious cycle, which explains the frequent parallel occurrence of arteriosclerosis and IHD, an association that appears to be linked by the same cause, comprises a common vulnerability to deleterious adrenergic actions on the myocardium, lipid metabolism, and vascular system alike, rather than viewing CAD and IsHD as having a putative cause and effect relationship as commonly thought. Adrenergic actions can also cause the abnormal lipid metabolism that is associated with CAD and IsHD by catecholamine-induced metabolic actions on lipid mobilization by activation of phospholipases. This may also be part of toxic catecholamine hypermetabolic actions by enhancing deleterious cholesterol and lipid actions in damaging coronary vessels by plaque formation as well as inducing obstructive coronary spasm and platelet aggregation. This may also cause direct toxic necrosis on the myocardium as well as atherosclerosis in blood vessels. In fact, drugs that inhibit adrenergic actions like propranolol, reserpine, and guanethidine all inhibit arteriosclerosis induced by hypercholesterolemia in experimental animals and prevent carotid vascular disease (associated with stroke) in humans. The concomitant development of myocardiopathy and coronary vascular lesions or coronary and carotid artery intimal medial thickening by catecholamine toxicity is reflected by the frequent primary presentation of patients with catecholamine-secreting pheochromocytoma with cardiovascular disease, ie, hypertension arrhythmias, AMI, SCD, CHF, and vascular disease, which represents a clear example of the primary deleterious impact of catecholamines on the entire cardiovascular system causing adrenergic cardiovascular disease. Thus, like myocardiopathy, CAD and atherosclerosis in general may be the consequences of or a complication of catecholamine actions rather than its putative cause. This report shows how prophylactic bretylium not only prevents arrhythmias but prevents myocardial necrosis, shock, CHF, maintains or restores normal contractility, and lowers mortality in AMI patients by inducing adrenergic blockade.

Cutaneous vasoconstrictor response to whole body skin cooling is altered by time of day.

To test for a diurnal difference in the vasoconstrictor control of the cutaneous circulation, we performed whole body skin cooling (water-perfused suits) at 0600 (AM) and 1600 (PM). After whole body skin temperature (T(sk)) was controlled at 35 degrees C for 10 min, it was progressively lowered to 32 degrees C over 18-20 min. Skin blood flow (SkBF) was monitored by laser-Doppler flowmetry at three control sites and at a site that had been pretreated with bretylium by iontophoresis to block noradrenergic vasoconstriction. After whole body skin cooling, maximal cutaneous vascular conductance (CVC) was measured by locally warming the sites of SkBF measurement to 42 degrees C for 30 min. Before whole body skin cooling, sublingual temperature (T(or)) in the PM was significantly higher than that in the AM (P < 0.05), but CVC, expressed as a percentage of maximal CVC (%CVC(max)), was not statistically different between AM and PM. During whole body skin cooling, %CVC(max) levels at bretylium-treated sites in AM or PM were not significantly reduced from baseline. In the PM, %CVC(max) at control sites fell significantly at T(sk) of 34.3 +/- 0.01 degrees C and lower (P < 0.05). In contrast, in the AM %CVC(max) at control sites was not significantly reduced from baseline until T(sk) reached 32.3 +/- 0.01 degrees C and lower (P < 0.05). Furthermore, the decrease in %CVC(max) in the PM was significantly greater than that in AM at T(sk) of 33.3 +/- 0.01 degrees C and lower (P < 0.05). Integrative analysis of the CVC response with respect to both T(or) and T(sk) showed that the cutaneous vasoconstrictor response was shifted to higher internal temperatures in the PM. These findings suggest that during whole body skin cooling the reflex control of the cutaneous vasoconstrictor system is shifted to a higher internal temperature in the PM. Furthermore, the slope of the relationship between CVC and T(sk) is steeper in the PM compared with that in the AM.

Advanced cardiac life support antiarrhythmic drugs.

As exemplified in this discussion of ACLS antiarrhythmic drugs, the evidence-based evaluation process has created a high standard for the acceptance and ranking of therapies for cardiac arrest. This process also has identified critical areas needing further investigation, fostered a healthy sense of discomfort with the adequacy of our present interventions for cardiac arrest, and hopefully will continue to spur the science while sifting the dogma out of CPR.

Paro circulatorio por fibrilación ventricular (1ª parte) / Circulatory arrest due to ventricular fibrillation (Part I)

La velocidad y la amplitud de las ondas fibrilatorias son una expresión, en cierta manera, de las condiciones funcionales del miocardio y de su grado de oxigenación. Se reconocen tres tipos de ondas fibrilatorias. A) Fibrilación convulsiva o gruesa: con ondas fibrilatorias de alta frecuencia (>150/minuto y entre 0,5 y 1 mV de amplitud). Observando directamente al corazón, el órgano se sacude violentamente como si convulsivara. B) Fibrilación trémula o fina: la frecuencia sigue siendo alta (>100/minuto) pero de menor amplitud y las ondas recorren en forma anárquica la superficie de la pared ventricular. Esta fase es consecuencia del gran consumo de oxígeno de la fase anterior. Dura de 3 a 5 minutos. C) Fibrilación hipotónica o lenta: las ondas fibrilatorias son anchas, de baja amplitud y baja frecuencia. (>100/minuto), el corazón luce cianótico, dilatado e hipotónico. Puede durar entre 5 y 15 minutos hasta que el corazón para totalmente en asistolia. Un corazón globalmente hipóxico difícilmente se fibrile en forma espontánea. El corazón debe ser desfibrilado durante las fases de fibrilación rápida. La desfibrilación es un intento de despolarizar globalmente a todo el corazón mediante una descarga eléctrica, y con ello producir una asistolia de breve duración durante la cual el corazón tiene la oportunidad de reanudar su actividad normal a partir de la activación espontánea del marcapaso natural, es decir, el nodo sinusal, y arrancar con ritmo sinusal. Estudios anteriores con descargas de baja energía (175-200 joules para un adulto) no lograron demostrar beneficio alguno de choques iniciales inferiores a 2 j/kg y choques en rápida sucesión de 3 a 4 j/kg (apróximadamente 200 a 400 joules de energía). Según el protocolo de la American Heart Association, el paciente debe ser desfibrilado con dos primeros choques de 2 a 3 j/kg. en rápida sucesión. Y si éstos fracasan deberá recibir un tercero de 4 j/kg. Los tres choques deben hacerse en rápida sucesión (no todos los autores concuerdan con este criterio), sin intervención medicamentosa intermedia y sin levantar las paletas del lugar, para evitar modificaciones en la impedancia transtorácica y lesiones de la piel (eritema, edema) en otras regiones del tórax. En el texto se analiza también el efecto de los medicamentos habitualmente utilizados en la reanimación cardíaca, sus indicaciones e inconvenientes.

Paro circulatorio por fibrilación ventricular (1¬ parte) / Circulatory arrest due to ventricular fibrillation (Part I)

La velocidad y la amplitud de las ondas fibrilatorias son una expresión, en cierta manera, de las condiciones funcionales del miocardio y de su grado de oxigenación. Se reconocen tres tipos de ondas fibrilatorias. A) Fibrilación convulsiva o gruesa: con ondas fibrilatorias de alta frecuencia (>150/minuto y entre 0,5 y 1 mV de amplitud). Observando directamente al corazón, el órgano se sacude violentamente como si convulsivara. B) Fibrilación trémula o fina: la frecuencia sigue siendo alta (>100/minuto) pero de menor amplitud y las ondas recorren en forma anárquica la superficie de la pared ventricular. Esta fase es consecuencia del gran consumo de oxígeno de la fase anterior. Dura de 3 a 5 minutos. C) Fibrilación hipotónica o lenta: las ondas fibrilatorias son anchas, de baja amplitud y baja frecuencia. (>100/minuto), el corazón luce cianótico, dilatado e hipotónico. Puede durar entre 5 y 15 minutos hasta que el corazón para totalmente en asistolia. Un corazón globalmente hipóxico difícilmente se fibrile en forma espontánea. El corazón debe ser desfibrilado durante las fases de fibrilación rápida. La desfibrilación es un intento de despolarizar globalmente a todo el corazón mediante una descarga eléctrica, y con ello producir una asistolia de breve duración durante la cual el corazón tiene la oportunidad de reanudar su actividad normal a partir de la activación espontánea del marcapaso natural, es decir, el nodo sinusal, y arrancar con ritmo sinusal. Estudios anteriores con descargas de baja energía (175-200 joules para un adulto) no lograron demostrar beneficio alguno de choques iniciales inferiores a 2 j/kg y choques en rápida sucesión de 3 a 4 j/kg (apróximadamente 200 a 400 joules de energía). Según el protocolo de la American Heart Association, el paciente debe ser desfibrilado con dos primeros choques de 2 a 3 j/kg. en rápida sucesión. Y si éstos fracasan deberá recibir un tercero de 4 j/kg. Los tres choques deben hacerse en rápida sucesión (no todos los autores concuerdan con este criterio), sin intervención medicamentosa intermedia y sin levantar las paletas del lugar, para evitar modificaciones en la impedancia transtorácica y lesiones de la piel (eritema, edema) en otras regiones del tórax. En el texto se analiza también el efecto de los medicamentos habitualmente utilizados en la reanimación cardíaca, sus indicaciones e inconvenientes. (AU)

Association of drug therapy with survival in cardiac arrest: limited role of advanced cardiac life support drugs.

OBJECTIVE: To generate hypotheses regarding the association of standard Advanced Cardiac Life Support (ACLS) drugs with human cardiac arrest survival. METHODS: This observational cohort study was conducted over a two-year period in the wards, intensive care units, and EDs of two tertiary care hospitals. Included werc adult patients who suffered cardiac arrest either inside or outside the hospital and who required epinephrine according to standard ACLS guidelines. Six standard ACLS drugs (given while CPR was in progress) were assessed for association with survival from resuscitation to one hour and to hospital discharge by univariate and multivariate logistic regression analyses. RESULTS: In the 529 patients studied, initial cardiac rhythm had no impact on the association between drug administration and survival. The time of drug administration (quartile of ACLS period) was associated with resuscitation for atropine (p < 0.05) and lidocaine (p < 0.01). The odds ratios (95% CIs) for successful resuscitation, after multivariate adjustment for potential confounders, were: a respiratory initiating cause, 3.7 (2.1 -6.4); each 5-minute increase in CPR-ACLS interval, 0.5 (0.4-0.7); each 5-minute duration of ACLS. 0.9 (()1.8- 1.0; atropine, 1.2 (1.0-1.3); bretylium. (0.4 (0.1-1.1); calcium 0.8 (0.2-2.4); lidocaine, 0.9 (0.7-1.1); procainamide. 21.0 (5.2-84.0) d sodium bicarbonate 1.2 (1.0-1.6). All other potential confounding variables entered into the model were not significantly associated with resuscitation. CONCLUSION: Initiating cause of arrest, time to ACLS, and duration of ACLS were important correlates of survival. Other than procainaimide, standard ACLS drugs had relatively little association with survival, but timing of administration may be an important factor. Further research using definitive large randomized controlled trials is warranted to assess the role of drug therapy in improving cardiac arrest survival.

Bretylium decreases and verapamil increases defibrillation threshold in pigs.

BACKGROUND: Patients with ischemic heart disease may require antianginal and/or antiarrhythmic regimes. These patients may also be candidates for implantable defibrillators. The effects of antiarrhythmics, such as bretylium, or calcium antagonists, such as verapamil, nifedipine, or diltiazem on internal defibrillation efficacy have been inconsistent or are unknown. METHODS AND RESULTS: The effects of bretylium and verapamil on the energy requirements for ventricular defibrillation threshold (DFT) were determined in 92 open-chest anesthetized pigs. Triplicate DFTs were determined before and after intravenous administration of saline or one of four doses of verapamil, or saline or one of three doses of bretylium, in a balanced random order. Bretylium elicited a dose dependent reduction of DFT (F = 2.72 at 3 degrees and 36 degrees of freedom). DFT was significantly reduced with the highest dose of bretylium, (from 5.9 +/- 0.6 J to 4.7 +/- 0.6 J, mean +/- S.E.M.; P < 0.01). However, cardiac massage was sometimes needed at this dose due to low blood pressure immediately after defibrillation. In contrast, there was a positive correlation between DFT and serum verapamil concentration (r = 0.54, P < 0.001). The highest dose of verapamil significantly increased DFT (from 6.3 +/- 0.6 J to 8.2 +/- 1.1 J; P < 0.05), at a serum verapamil concentration of 86.6 +/- 6.8 ng/mL. CONCLUSIONS: These data indicate that bretylium decreases while verapamil increases the minimum energy requirement for internal defibrillation. Caution is warranted in patients who may be hemodynamically comprised and may be candidates for bretylium therapy or in patients who have marginal DFT value who might be candidates for verapamil therapy.

The technique of reversing ventricular fibrillation: improve the odds of success with this five-phase approach.

Early, repeated defibrillation is the key to managing ventricular fibrillation (VF). To maximize the likelihood of success, use this five-phase approach, modified from the advanced cardiac life support protocols. Phase I: When a patient is found in VF and with no pulse or signs of life, attempt electrical reversion with a 200-wsec shock, followed if necessary by a 300-wsec and a 360-wsec shock. Phase II: Manage reversible causes of VF with orotracheal intubation, hyperventilation, and epinephrine. Phase III: Use intravenous lidocaine aggressively, followed by a 360-wsec shock. Phase IV: Give bretylium and magnesium sulfate by intravenous push, again followed by a 360-wsec shock. Phase V: Treat refractory VF with repeated 360-wsec shocks, and give further doses of the anti-arrhythmic agents.

Influence of ion-pair formation on the pharmacokinetic properties of drugs. Pharmacokinetic interactions of bretylium and hexylsalicylic acid in rabbits.

The simultaneous i.v. administration of equimolar doses of bretylium and hexylsalicylic acid results in an increase in plasma area under the curve value of both substances in comparison with their separate administration. The higher plasma levels of both compounds were associated with a reduced renal excretion and an increased biliary elimination. However, the increase in biliary excretion did not compensate for the reduced elimination of bretylium and hexylsalicylic acid via the kidney. The results presented in this paper give further evidence that ion-pairing in-vivo may result in altered pharmacokinetics of drugs particularly due to changes in biliary or renal excretion.

Influence of the ion-pair-formation on the pharmacokinetic properties of drugs. Part 5: Influence of ion-pair-formation on elimination of bretylium and hexylsalicylic acid in rats.

Following i.v. administration of the hydrophilic drug bretylium (1) and the lipophilic hexylsalicylic acid (2) in rats the plasma levels of 2 were increased due to an increased intestinal reabsorption of 2. Under these conditions the biliary eliminated amount of 2 was 8 times higher than that following the administration of 2 alone. The eneteroheptic circulation of 2 was found to be interrupted following i.v. administration of 1 and 2 and additional oral administration of an anionic exchanger. Then the plasma levels of 2 were not influenced by 1. On other hand the plasma levels of 2 appear to be too low in order to influence those of 1.

Extreme pyrexia during bretylium administration.

Body temperatures exceeding 41.1 degrees C (106 degrees F) occur with relatively few conditions. In the unusual case reported here, the patient's temperature reached 42.3 degrees C (108.2 degrees F) during intravenous administration of bretylium for refractory ventricular fibrillation. The temperature started to drop as soon as the infusion was stopped and was close to normal within four hours. This appears to be the first report of extreme pyrexia resulting from use of this agent.

Influence of ion-pair-formation on the pharmacokinetic properties of drugs. Part 4: Influence of hexylsalicylic acid on the pharmacokinetics of bretylium.

Based on in vitro results it was found that the pharmacokinetic parameters of the hydrophilic drug bretylium (2) can be influenced by an ion-pair-formation with the lipophilic hexylsalicyclic acid (1). After simultaneous i.v. application of 1 and 2 on rabbits a significant increase of the AUC of 2 was observed. Under these conditions a marked increase of the AUC and the MRT of 1 was also obtained, since the blood levels of 2 are high enough for such an influence. A combined rectal application of 1 and 2 causes an increase of the AUC of 2.

Clinical suppression of refractory ventricular tachycardia with oral bretylium not predicted by electrophysiologic drug testing.

We report the findings in a patient in whom intravenous bretylium was the only effective agent to suppress refractory ventricular tachycardia and ventricular fibrillation. After attempts to switch the patient to amiodarone and bethanidine (an oral analogue of bretylium) caused proarrhythmic effects, he was successfully converted to oral therapy with bretylium. Electrophysiologic testing was not predictive of the clinical response from oral bretylium. To our knowledge, this is the first report of a proarrhythmic effect from bethanadine and it suggests a divergence in the actions of various class 3 antiarrhythmic agents.

Clinical pharmacokinetics of bretylium.

Bretylium is a class III antiarrhythmic agent which is used for the management of serious and refractory ventricular tachyarrhythmias. It exhibits a complex pharmacokinetic profile which is poorly understood. The drug is poorly absorbed following oral administration, and its oral bioavailability is in the region of 18 to 23%. Peak plasma concentrations occur at 1 to 9 hours after oral ingestion, and following oral doses of 5 mg/kg average 76 ng/ml, which is 28-fold lower than those achieved after equivalent intravenous doses. Approximately 75% of a bretylium dose is absorbed within 24 hours of intramuscular administration. Peak plasma concentrations occur at 30 to 90 minutes after intramuscular administration and range from 670 to 1500 ng/ml in subjects receiving 4 mg/kg. Bretylium is negligibly bound to plasma proteins (1-6%). Although drug tissue concentrations have not been reported in humans, high values for the apparent volume of distribution suggest extensive tissue binding. In animals, bretylium is progressively taken up by the myocardium over a period of 12 hours, and at 12 hours after bolus administration, myocardial concentrations exceed plasma concentrations 6 to 12 times. It is also avidly taken up by adrenergic nerves in animals. Bretylium is almost entirely cleared by the renal route and its total body clearance is closely correlated with renal clearance. Available data suggest that bretylium exhibits a complex pharmacokinetic profile which has been described by a 3-compartment model in subjects receiving intravenous dosing. The terminal elimination half-life ranges from 7 to 11 hours following oral, intramuscular and intravenous administration, and renal clearance is about 600 ml/min after intravenous administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Rationale of combination antiarrhythmic drug therapy.

In summary, antiarrhythmic combinations have been explored as a matter of clinical necessity in many instances, and clinical circumstance has led to attempted combination therapy with two, and sometimes more, drugs. Few controlled studies using a specific combination have been performed. Therapy is thus usually empiric, based on available clinical, electrophysiologic and pharmacologic information. Nonetheless, certain general impressions are available, which may form the basis for clinical decisions and for structuring future trials (Table 6). Although single-drug antiarrhythmic therapy continues to be advisable, in certain instances combined-drug therapy may be appropriate and efficacious. The importance of potential adverse drug interactions must also be appreciated.