New insights into the definition and meaning of proarrhythmia during initiation of antiarrhythmic drug therapy from the Cardiac Arrhythmia Suppression Trial and its pilot study. The CAST and CAPS Investigators

Cardiovascular Manifestations of Acute Intracranial Lesions: Pathophysiology, Manifestations, and Treatment

The objective of this article was to review the effects of acute intracranial lesions on myocardial function. The authors reviewed scientific and clinical literature retrieved from a computerized MEDLINE search from January 1965 through January 2002. Pertinent literature was referenced, including clinical and laboratory investigations, to demonstrate the effects of acute intracranial lesions on the cardiovascular system. The literature was reviewed to summarize the mechanisms of cardiac damage and clinical manifestations and treatment of cardiovascular dysfunction caused by acute intracranial lesions. Myocardial damage and rhythm disturbances were shown to occur with acute intracranial neurological disease. The subgroup of patients used in this study formed a substantial pool of cardiac donors for cardiac transplantation. The pathophysiology of myocardial dysfunction and the optimal management continues to be a source of debate. In this article, the authors will review the anatomy, the available evidence of the pathophysiology, and the management of this complex group of patients. They will also discuss areas that need to be further investigated. Cardiovascular effects of acute intracranial lesions are common and contribute to increased morbidity and mortality.

Combination drug therapy for patients with intractable ventricular tachycardia associated with right ventricular cardiomyopathy

BACKGROUND

Drug therapy for patients with right ventricular (RV) cardiomyopathy refractory to single-drug therapy and ablation has not been well defined.

METHODS

We reviewed our entire RV cardiomyopathy database (31 patients) and found four patients presenting with ventricular arrhythmias of RV origin refractory to single-drug therapy. These patients underwent complete evaluation for arrhythmogenic right ventricular cardiomyopathy (ARVC).

RESULTS

Following the revised 2010 task force criteria, of these four patients, three were diagnosed with ARVC, and one with cardiac sarcoidosis. These patients proved to be refractory to drug monotherapy and either failed or deemed to not be candidates for endocardial ablation. Their arrhythmias were ultimately controlled with combinations of sotalol, flecainide, and mexiletine.

CONCLUSIONS

In our experience, combination drug therapy is an effective treatment strategy for patients with ventricular tachycardia refractory to monotherapy and, in some cases, ablation. In addition, flecainide appears to be safe and effective for those with RV cardiomyopathy without significant left ventricular dysfunction.

Intravenous lidocaine and mexiletine in the management of trigeminal autonomic cephalalgias

Lidocaine and mexiletine are class 1B antiarrhythmic drugs that act on sodium channels. Lidocaine is also an important anesthetic and topical agent that is useful in the treatment of multiple pain disorders, and mexiletine is commonly used for neuropathic pain and myotonia. Both intravenous lidocaine and mexiletine are increasingly used to treat pain syndromes and appear to be particularly effective in neuropathic pain. This suggests a role for these agents in patients with headache disorders. This article describes the role of intravenous lidocaine and mexiletine in the management of headache and trigeminal autonomic cephalalgias based on the published literature to date and provides practical guidelines for their use.

Evidence for the binding of β-adrenoceptor blockers to microsomal Na+/K+-ATPase in guinea pig heart preparations

We reported in a previous study that β-adrenoceptor blockers inhibit the Mg2+-dependent ATP-hydrolytic function of Na+/K+-ATPase. To determine if this action is a result of binding of β-blockers to the receptor sites that bind the digitalis glycosides, we performed displacement binding assays of eight β-blockers with [3H]-ouabain (OUA) in guinea pig myocardial microsomal preparations. In the first series of experiments, 10-200 µM of the β-blockers were displaced with 250 nM OUA. In the second set of experiments, 10-500 nM of OUA was displaced using 200 µM of the β-blockers. The drugs showed concentration-dependent receptor occupancy at the different OUA levels. Propranolol (PPN), metoprolol (MTP), and sotalol (STL) showed the strongest binding; nadolol (NDL), indenolol (IDN), and atenolol (ATN) had intermediate binding; carazolol (CRZ) and celiprolol (CLP) had the weakest binding properties. The results suggest that β-blockers may compete for the same binding sites with ouabain in their inhibition of the Na+/K+-ATPase. These actions may contribute to the mechanism for some of their cardiac effects, especially their proarrhythmic and arrhythmogenic actions.Key words: β-adrenoceptor blockers, antiarrhythmic agents, arrhythmogenic effects, Na+/K+-ATPase, ouabain binding.

Long-term outcome of patients with drug-refractory atrial flutter and fibrillation after single- and dual-site right atrial pacing for arrhythmia prevention

OBJECTIVES

An initial crossover study comparing dual- and single-site right atrial pacing was performed followed by a long-term efficacy and safety evaluation of dual-site right atrial pacing in patients with drug-refractory atrial fibrillation (AF). Also examined was the efficacy of two single-site right atrial pacing modes (high right atrium and coronary sinus ostium) and the long-term need for cardioversion, antithrombotic and antiarrhythmic drug therapies during dual-site atrial pacing.

METHODS

Thirty consecutive patients with drug-refractory symptomatic AF and documented primary or drug-induced bradycardia were implanted with a dual chamber rate-responsive pacemaker and two atrial leads. Single-site atrial pacing was performed at the high right atrium or the coronary sinus ostium. Continuous atrial pacing was maintained.

RESULTS

Mean arrhythmia-free intervals increased from 9+/-10 days in the control period preceding implant to 143+/-110 days (p < 0.0001) in single-site right atrial pacing and 195+/-96 days in dual-site right atrial pacing (p < 0.005 versus single-site pacing and p < 0.0001 versus control). Dual-site right atrial pacing significantly increased the proportion of patients free of AF recurrence (89%) as compared to single-site right atrial pacing (62%, p = 0.02). High right atrial pacing and coronary sinus ostial pacing had similar efficacy for AF prevention. Effective rhythm control was achieved in 86% of patients during dual right atrial pacing. Seventy-eight percent of patients at 1 year and 56% at 3 years remained free of symptomatic AF. The need for cardioversion was reduced after pacemaker implant (p < 0.05) and antithrombotic therapy was reduced (p < 0.06) without any thromboembolic event. Coronary sinus ostial lead dislodgement was not observed after discharge.

CONCLUSIONS

Atrial pacing in combination with antiarrhythmic drugs eliminates or markedly reduces recurrent AF. Prevention of AF is enhanced by dual-site right atrial pacing. High right atrial and coronary sinus ostial pacing do not differ in efficacy. Dual-site right atrial pacing is safe, achieves long-term rhythm control in most patients, decreases the need for cardioversion, and antithrombotic therapy can be selectively reduced.

Proarrhythmia

Proarrhythmia is defined as the provocation of a new arrhythmia or the aggravation of a pre-existing one during therapy with a drug at doses or plasma concentrations below those considered to be toxic. Suggested criteria for proarrhythmia include (1) the new appearance of a sustained ventricular tachyarrhythmia; (2) change from a nonsustained to a sustained tachyarrhythmia; (3) acceleration of tachycardia rate; or (4) the new appearance of a clinically significant bradyarrhythmia or conduction defect. Proarrhythmia can be the direct result of a drug's electrophysiologic effects on conduction velocity, refractoriness, and automaticity. However, it may also be the result of metabolic abnormalities, changes in autonomic state, or drug/drug interactions that amplify or alter the drug's electrophysiologic effects. Some forms of ventricular proarrhythmia, such as torsade de pointes, are difficult to forecast and occur in patients with structurally normal hearts as well as in those with serious heart disease. Other forms of ventricular proarrhythmia, such as monomorphic ventricular tachycardia, occur predominantly in patients with structural heart disease or pre-existing ventricular arrhythmia. Atrial flutter with 1 : 1 conduction and bradyarrhythmias can be manifestations of proarrhythmia, particularly during drug therapy for atrial fibrillation. In patients with pacemakers or implantable cardiac defibrillators, antiarrhythmic drugs can change pacing thresholds and can alter the ability of a device to recognize or terminate a sustained ventricular tachyarrhythmia.

Signal-averaged ECG in patients with antidepressant therapy

The signal-averaged electrocardiography (SAECG) identifies patients at risk of ventricular arrhythmias and sudden cardiac death. Since the similarity has been known of the pharmacology of class I antiarrhythmics and tricyclic antidepressants, the potential proarrhythmic effects of antidepressants has become a particular problem. The influence of sodium channel blocking antidepressant drugs on the SAECG time-domain parameters was evaluated, using high-pass filters of 25 Hz and 40 Hz. SAECG was performed in 11 depressed patients with normal cardiac status before and for 4 weeks after antidepressant initiation. At the filter setting of 25 Hz, a significant worsening of all studied SAECG parameters (filtered QRS duration, low-amplitude signal duration, root mean square voltage in the first and in the last 40 ms of the filtered QRS) was found in our patient group. Using a 40 Hz high-pass filter, the results were similar. Antidepressant therapy significantly prolonged filtered QRS duration, significantly reduced root mean square voltages in the first and in the last 40 ms of the filtered QRS and non-significantly prolonged low amplitude signal duration. Amitriptyline and maprotiline induced late potentials (LP) in 2 patients at 40 Hz high pass filter setting. No patient had LP at 25-250 Hz. Our pilot study indicates that sodium channel blocking antidepressant drugs may affect SAECG variables similarly to class I antiarrhythmics. SAECG might be useful in categorizing of antidepressant agents and risk stratification of psychiatric patients.

Proarrhythmia with class III antiarrhythmic drugs: definition, electrophysiologic mechanisms, incidence, predisposing factors, and clinical implications

Antiarrhythmic drugs can and do induce unexpected and sometimes fatal reactions by either producing new symptomatic arrhythmias or by aggravating existing arrhythmias. The definition of proarrhythmia has changed since controlled clinical studies showed a dichotomy between arrhythmia suppression and mortality. The nature of proarrhythmic reactions is linked to the electrophysiologic effects of various antiarrhythmic drugs. Whereas Class I agents without accompanying effects on repolarization generally produce ventricular tachycardia (often incessant) or fibrillation, Class III agents typically produce torsades de pointes that may deteriorate into ventricular fibrillation. The precise mechanism of torsades de pointes is not fully elucidated, although early after-depolarization and increases in spatial or temporal dispersion of repolarization are likely possibilities. Proarrhythmic risk is lowest for amiodarone and is probably related to the drug's complex electrophysiologic profile. The incidence of torsades with sotalol increases with dose and the baseline values of the QT interval; the incidence with d-sotalol and other pure Class III agents remains unclear. Prospective, randomized, placebo-controlled studies to evaluate this are under way. The fact that d-sotalol increases mortality in postinfarction patients suggests that it may possibly be a common property of most, if not all, pure Class III compounds. The ongoing clinical trials with various Class III agents are likely to provide the critical information on this important therapeutic issue.