A randomized clinical trial of the noninvasive and invasive approaches to drug therapy for ventricular tachycardia: long-term follow-up of the Calgary trial

Ventricular Tachycardia Following Surgical Repair of Complex Congenital Heart Disease

A nine year old boy with complex congenital heart disease requiring right ventricular outflow tract surgery and palpitations had inducible monomorphic ventricular tachycardia at 300 bpm by programmed ventricular stimulation. He was treated with enteral phenytoin. With a therapeutic plasma level, repeat electrophysiological study was negative for inducible ventricular tachycardia using an aggressive pacing protocol. An insertable loop recorder was implanted, and the family was prescribed an automatic external defibrillator. The decision to not place an implantable cardioverter-defibrillator was based upon anticipated need for serial cardiac MRI scans to monitor the effect of progressive outflow tract stenosis and regurgitation.

The implantable cardioverter-defibrillator: does everybody need one?

The implantable cardioverter-defibrillator (ICD) has emerged as an effective, but expensive, therapy for arrhythmic sudden cardiac death. ICD use has been increasing by 20% to 30% per year. Clinical trials have shown that the ICD can be effective for both the primary prevention and the secondary prevention of sudden cardiac death in selected populations. Despite the available trial evidence, several issues pertaining to ICD use remain unresolved, including the treatment of patients not represented in clinical trials, the optimal selection of patients who will benefit from an ICD, the duration of benefit from an ICD, the quality of life for patients with an ICD, and both the cost-effectiveness and the cost impact of the ICD. These considerations are discussed in this article.

Can antiarrhythmic agents be selected based on mechanism of action?

When selecting an antiarrhythmic agent the clinician needs to be able to accurately predict the probability that a particular drug will serve its intended purpose in a given patient. This is difficult because of the complexity of variables which govern the relationship between drug administration and clinical outcome. The efficacy of a drug may potentially be predicted from its mechanism of action. At least two classifications of antiarrhythmic agents based on mechanism of action have been proposed. The Vaughan Williams classification is based on the predominant electrophysiological effects of a drug on the action potential. In the Sicilian Gambit approach, a number of potential targets ('vulnerable parameters') for drug action are identified and antiarrhythmic drugs or substances that affect cardiac electrophysiology are characterised by their actions on each of these. The usefulness of these classification systems in predicting antiarrhythmic drug efficacy are limited. Furthermore, in the Vaughan Williams classification not all drugs in the same class have identical effects, whereas some drugs in different classes have overlapping actions. The Sicilian Gambit requires in-depth knowledge regarding cellular and molecular targets of antiarrhythmic agents which may make it intimidating or simply impractical for regular clinical use. Surrogate measures such as 24-hour Holter monitoring and programmed electrical stimulation have been used to predict anti-arrhythmic drug efficacy. However, studies such the Cardiac Arrhythmia Suppression Trial (CAST) have shown that suppression of ventricular ectopy on Holter monitoring does not necessarily correlate with improved survival and may in fact be dangerous. Conversely, studies using programmed electrical stimulation to assess drug effect on variables such as tachycardia inducibility, refractory period and ventricular tachycardia cycle length show that suppression of tachycardia inducibility, prolongation of refractory period and prolongation of ventricular tachycardia cycle length, are all associated with reduced recurrence of tachycardia and possibly improved survival. The most practical use of the current classification systems applied to antiarrhythmic agents may be in their ability to predict with reasonable accuracy, the risk and type of proarrhythmia based on the mechanism of action of an agent.

Drug therapy of sustained ventricular tachyarrhythmias. Is there still a role?

This article provides a review of the risks faced by patients with sustained ventricular tachycardia (VT) or ventricular fibrillation (VF) in the absence of a reversible or transient cause so that the goals of therapy can be clearly defined. The therapeutic approaches that have been proposed to achieve these goals are outlined and evidence comparing these various approaches to therapy is then summarized in order to propose an algorithm for the optimal use of antiarrhythmic drug therapies as primary therapy for selected VT/VF patients. Options for the ancillary uses of antiarrhythmic drug therapies in ICD patients are considered.

Electrophysiologic parameters to predict clinical recurrence of ventricular tachycardia in patients under electrophysiologic study-guided effective pharmacological therapy

Although an electrophysiologic study (EPS) is the most reliable method for selecting the treatment for a patient with sustained ventricular tachycardia (VT), VT recurrence may occur even during EPS-guided effective therapy. Electrophysiologic parameters were compared between patients with and without arrhythmic events under EPS-guided effective therapy to identify the predictive parameters of VT recurrence during the clinical course. The study population consisted of 77 consecutive patients with sustained VT who were receiving long-term pharmacological therapy that was demonstrated to be effective by the EPS assessment. The VT induction protocol employed 1-3 extrastimuli and rapid ventricular pacing at 2 right ventricular sites and 1 left ventricular site, and isoproterenol was infused when VT was not induced. To determine the 'effective' antiarrhythmic drug, all sustained ventricular arrhythmias had to be prevented during the whole induction protocol, but repetitive ventricular responses (RVR) were allowed to remain for up to 5 beats when they were in the same QRS configurations as the clinical VT and up to 12 beats when they were in polymorphic QRS configurations. The effective refractory periods (ERPs) at the 3 ventricular pacing sites and their difference (i.e., ERP-dispersion) and the maximum number of RVR beats were evaluated in an EPS during the control state and at the time of drug assessment. In the comparison of patients with and without VT recurrence, there was no significant difference in clinical characteristics or ERPs, but the deltaERP-dispersion (i.e., the increase in ERP-dispersion caused by the antiarrhythmic drug) and the maximum number of RVRs were significantly smaller in the group of patients without VT recurrence (deltaERP-dis, -3+/-8 vs. 6+/-12, p = 0.0027; maxRVR, 3+/-3 vs. 5+/-4, p = 0.0160). The VT recurrence rate was significantly lower in the patients with deltaERP-dis < or =0 or maxRVR<6 in comparison with the others (p = 0.01 14 and p = 0.0360). Patients with VT recurrence showed greater deltaERP-disp and a longer duration of RVRs at the time of drug assessment in comparison with the patients without VT recurrence. The prognosis of patients under EPS-guided therapy may be improved by the use of stricter criteria for drug assessment in the EPS, although this may decrease the number of drug responders determined in the EPS.

A decade of clinical trial developments in postmyocardial infarction, congestive heart failure, and sustained ventricular tachyarrhythmia patients: from CAST to AVID and beyond. Cardiac Arrhythmic Suppression Trial. Antiarrhythmic Versus Implantable Defibrillators

Multiple trials using antiarrhythmic drugs, pharmacologic therapy, and implantable cardioverter defibrillators have been performed in an attempt to improve survival in patients: (1) postmyocardial infarction; (2) with congestive heart failure, with and without nonsustained ventricular tachycardia; and (3) with sustained ventricular tachycardia and those who have survived an out-of-hospital cardiac arrest. This article reviews some of the key findings and limitations of completed and ongoing trials. We also make recommendations for the current treatment of such patients based on the results of these trials.

Definition of predicted effective antiarrhythmic drug therapy for ventricular tachyarrhythmias by the electrophysiologic study approach: randomized comparison of patient response criteria

OBJECTIVES

We sought to compare efficacies of therapy for ventricular tachyarrhythmias selected by programmed stimulation using two different patient response efficacy criteria: <5 versus <16 repetitive ventricular responses.

BACKGROUND

Therapy selection for ventricular tachyarrhythmias by programmed stimulation requires definition of a patient response that predicts long-term efficacy. Such definitions have not been previously compared prospectively.

METHODS

Patients with sustained ventricular tachyarrhythmias were randomized to therapy selection using either the <5 or <16 repetitive response criterion of predicted effective therapy. The primary end point was sudden death or recurrence of ventricular tachyarrhythmia requiring intervention.

RESULTS

Predicted effective drug therapy was found for 23 (34%) of 68 patients randomized to the <5 criterion and 29 (36%) of 81 patients randomized to the <16 criterion (p = NS). Definition of therapy required 3.0 +/- 1.6 drug trials (mean +/- SD) in patients randomized to the <5 criterion and 2.9 +/- 1.8 trials in patients randomized to the <16 criterion (p = NS). Patients randomized to the <5 criterion had a lower 2-year probability of the primary end point (0.20 +/- 0.05) than did patients randomized to the <16 criterion (0.33 +/- 0.05, one-tailed p = 0.004). The advantage of the <5 criterion was also seen in subgroup analyses involving patients with and without an initial drug efficacy prediction.

CONCLUSIONS

The programmed stimulation approach to the selection of antiarrhythmic therapy for ventricular tachyarrhythmias using a patient response criterion of <5 repetitive ventricular responses results in a lower probability of recurrence of ventricular tachyarrhythmia than does use of a <16 repetitive response criterion.