Efficacy of intravenous propranolol for suppression of inducibility of ventricular tachyarrhythmias with different electrophysiologic characteristics in coronary artery disease

Pharmacologic Management for Ventricular Arrhythmias: Overview of Anti-Arrhythmic Drugs

Ventricular arrhythmias (Vas) are a life-threatening condition and preventable cause of sudden cardiac death (SCD). With the increased utilization of implantable cardiac defibrillators (ICD), the focus of VA management has shifted toward reduction of morbidity from VAs and ICD therapies. Anti-arrhythmic drugs (AADs) can be an important adjunct therapy in the treatment of recurrent VAs. In the treatment of VAs secondary to structural heart disease, amiodarone remains the most well studied and current guideline-directed pharmacologic therapy. Beta blockers also serve as an important adjunct and are a largely underutilized medication with strong evidentiary support. In patients with defined syndromes in structurally normal hearts, AADs can offer tailored therapies in prevention of SCD and improvement in quality of life. Further clinical trials are warranted to investigate the role of newer therapeutic options and for the direct comparison of established AADs.

Beta blockers as anti-arrhythmic agents

Although beta-adrenergic blocking agents are not always considered anti-arrhythmic drugs, the results of several recent trials have suggested an anti-arrhythmic mechanism for at least part of their mortality benefit in the treatment of chronic congestive heart failure. We review background experimental and clinical evidence for the anti-arrhythmic actions of beta-blockers and then review the results of published beta-blocker heart failure trials. A majority of trials showed improvement in overall survival as well as reduction in sudden death and ventricular arrhythmias with beta-blocker treatment. Although different effects were seen with different specific agents, these trials overall support a clinically significant anti-arrhythmic effect of several beta-blockers.

Beta-adrenergic blocking drugs as antifibrillatory agents

Beta-Adrenergic blockade is associated with a significant reduction in mortality in most patients with structural heart disease. Clinical trial data involving patients after myocardial infarction or with congestive heart failure demonstrate that a reduction in sudden death accounts for much of the observed mortality reduction. Beta-adrenergic blockade inhibits the proarrhythmic effects of both neural and humoral sympathetic stimulation and inhibits the vagal withdrawal that accompanies ischemia. Although it does not have a dramatic effect on spontaneous ectopy or inducible monomorphic ventricular tachycardia, experimental and clinical data suggest that it inhibits the development of ventricular fibrillation by several mechanisms.

Heart rate dynamics before spontaneous onset of ventricular fibrillation in patients with healed myocardial infarcts

The traditional methods of analyzing heart rate (HR) variability have failed to predict imminent ventricular fibrillation (VF). We sought to determine whether new methods of analyzing RR interval variability based on nonlinear dynamics and fractal analysis may help to detect subtle abnormalities in RR interval behavior before the onset of life-threatening arrhythmias. RR interval dynamics were analyzed from 24-hour Holter recordings of 15 patients who experienced VF during electrocardiographic recording. Thirty patients without spontaneous or inducible arrhythmia events served as a control group in this retrospective case control study. Conventional time- and frequency-domain measurements, the short-term fractal scaling exponent (alpha) obtained by detrended fluctuation analysis, and the slope (beta) of the power-law regression line (log power - log frequency, 10(-4)-10(-2) Hz) of RR interval dynamics were determined. The short-term correlation exponent alpha of RR intervals (0.64 +/- 0.19 vs 1.05 +/- 0.12; p <0.001) and the power-law slope beta (-1.63 +/- 0.28 vs -1.31 +/- 0.20, p <0.001) were lower in the patients before the onset of VF than in the control patients, but the SD and the low-frequency spectral components of RR intervals did not differ between the groups. The short-term scaling exponent performed better than any other measurement of HR variability in differentiating between the patients with VF and controls. Altered fractal correlation properties of HR behavior precede the spontaneous onset of VF. Dynamic analysis methods of analyzing RR intervals may help to identify abnormalities in HR behavior before VF.

Importance of beta blockade in the therapy of serious ventricular arrhythmias

Beta blockers have traditionally been considered relatively poor antiarrhythmic agents for patients with ventricular arrhythmias. This view is based on the observations that beta blockers are less effective in suppressing spontaneous ventricular ectopy or inducible ventricular arrhythmias than are the class I and class III agents. However, there are convincing data that beta blockers can have a clinically important antiarrhythmic effect and prevent arrhythmic and sudden death. Beta blockers have multiple potential effects that can contribute to a therapeutic antiarrhythmic action, including an antiadrenergic/vagomimetic effect, a decrease in ventricular fibrillation threshold, and prevention of a catecholamine reversal of concomitant class I/III antiarrhythmic drug effects. Postinfarction trials, recent congestive heart failure studies, and observations in patients who are at risk for sustained ventricular arrhythmias all suggest a potent antiarrhythmic effect of beta blockade.

Heart rate variability and dispersion of QT interval in patients with vulnerability to ventricular tachycardia and ventricular fibrillation after previous myocardial infarction

OBJECTIVES

This study was designed to compare QT dispersion measured from the standard 12-lead electrocardiogram and 24-h heart rate variability in patients with vulnerability to either ventricular tachycardia or ventricular fibrillation after a previous myocardial infarction.

BACKGROUND

Increased QT interval dispersion and reduced heart rate variability have been shown to be associated with vulnerability to ventricular tachyarrhythmias, but the data have mainly been pooled from patients with presentation of stable ventricular tachycardia and ventricular fibrillation.

METHODS

QT dispersion and time domain and two-dimensional vector analysis of heart rate variability were studied in 30 survivors of ventricular fibrillation with a previous myocardial infarction and with inducible unstable ventricular tachyarrhythmia by programmed electrical stimulation and in 30 postinfarction patients with clinical and inducible stable monomorphic sustained ventricular tachycardia. Both of these patient groups were matched, with respect to age, gender and left ventricular ejection fraction, with an equal number of postinfarction control patients without a history of arrhythmic events or inducible ventricular tachyarrhythmia and arrhythmia-free survival during a follow-up period of 2 years. Forty-five age-matched healthy subjects served as normal control subjects.

RESULTS

Standard deviation of all sinus intervals and long-term continuous RR interval variability analyzed from Poincaré plots were reduced in patients with vulnerability to ventricular fibrillation (p < 0.001 for both), but not in patients with ventricular tachycardia (p = NS for both), compared with postinfarction control subjects. Corrected QT (QTc) dispersion was significantly broader both in patients with ventricular fibrillation (p < 0.001) and in those with ventricular tachycardia (p < 0.05) than in matched postinfarction control subjects. Heart rate variability performed better than QTc dispersion in predicting vulnerability to ventricular fibrillation.

CONCLUSIONS

Increased QT dispersion is associated with vulnerability to both ventricular tachycardia and ventricular fibrillation. Low heart rate variability is specifically related to susceptibility to ventricular fibrillation but not to stable monomorphic ventricular tachycardia, suggesting that the autonomic nervous system modifies the presentation of life-threatening ventricular arrhythmias.

Dynamic analysis of heart rate may predict subsequent ventricular tachycardia after myocardial infarction

Dynamics analysis of RR interval behavior and traditional measures of heart rate variability were compared between postinfarction patients with and without vulnerability to ventricular tachyarrhythmias in a case-control study. Short-term fractal correlation of heart rate dynamics was better than traditional measures of heart rate variability in differentiating patients with and without life-threatening arrhythmias.

Frequency of sudden cardiac death and profiles of risk

The epidemiology of ventricular tachycardia/fibrillation (VT/VF) and sudden cardiac death (SCD) must be explored from multiple aspects, each of which contributes insights into the problem and no one of which exerts exclusive dominance for preventive or therapeutic strategies. These include: (1) population dynamics, using conventional epidemiologic approaches; (2) risk as a function of time from an index event; (3) conditioning risk factors, based on the presence of underlying disease states; (4) transient risk factors that are dynamic and trigger a potentially fatal event at a specific point in time; and (5) "response risk," which refers to individual susceptibility (possibly determined genetically) to the adverse effects of longitudinal and/or dynamic risk factors. Major inroads into profiling individual or population risk of SCD will require better understanding of each of these epidemiologic-clinical-physiologic interactions. The disciplines range from epidemiology, through clinical medicine, to membrane channel physiology, genetic determinants, and molecular biology.

The ESVEM trial: impact on treatment of ventricular tachyarrhythmias. Electrophysiologic Study Versus Electrocardiographic Monitoring

The ESVEM (Electrophysiologic Study Versus Electrocardiographic Monitoring) trial was a prospective, randomized study, initiated in 1983, to compare the outcome of patients in whom antiarrhythmic therapy was guided by serial electrophysiological study with the outcome of patients in whom therapy was guided by electrocardiographic monitoring. In a surprising finding, there was no difference in rates of arrhythmia recurrence or mortality between the two methods. Subsequent reanalyses using more stringent criteria for both methods or a combined assessment have not significantly improved the predictive accuracy of guided therapy. Because drug therapy in each limb was also randomized, a comparison of specific antiarrhythmic agents was also possible: sotalol therapy and the absence of previous antiarrhythmic drug therapy were associated with a reduction in arrhythmia recurrence. Survey data suggest that the results of this trial have influenced clinical practice.

Beta adrenergic blockade in the treatment of sustained ventricular tachycardia or ventricular fibrillation

The value of beta-blockers as antiarrhythmic drugs in patients with sustained VT or VF has received only little attention. This article summarizes the current state of knowledge regarding the identification of patients with sustained VT or VF with the highest benefit of beta-blockade. The antiarrhythmic mechanisms of beta-blockade and its efficacy as single or adjuvant therapy in patients with sustained VT or VF are reviewed. Current insights into the effects of beta-blockade in patients suffering from VT, in particular in the setting of heart failure, are discussed and future directions are considered.

Abnormalities in beat-to-beat dynamics of heart rate before the spontaneous onset of life-threatening ventricular tachyarrhythmias in patients with prior myocardial infarction

BACKGROUND

Beat-to-beat analysis of RR intervals can reveal patterns of heart-rate dynamics, which are not easily detected by summary measures of heart-rate variability. This study was designed to test the hypothesis that alterations in RR-interval dynamics occur before the spontaneous onset of ventricular tachyarrhythmias (VT).

METHODS AND RESULTS

Ambulatory ECG recordings from 15 patients with prior myocardial infarction (MI) who had spontaneous episodes of sustained VT during the recording and VT inducible by programmed electrical stimulation (VT group) were analyzed by plotting each RR interval of a sinus beat as a function of the previous one (Poincaré plot). Poincaré plots were also generated for 30 post-MI patients who had no history of spontaneous VT events and no inducible VT (MI control subjects) and for 30 age-matched subjects without heart disease (normal control subjects). The MI control subjects and VT group were matched with respect to age and severity of underlying heart disease. All the healthy subjects and MI control subjects showed fan-shaped Poincaré plots characterized by an increased next-interval difference for long RR intervals relative to short ones. All the VT patients had abnormal plots: 9 with a complex pattern, 3 ball-shaped, and 3 torpedo-shaped. Quantitative analysis of the Poincare plots showed the SD of the long-term RR-interval variability (SD2) to be smaller in all VT patients (52+/-14 ms; range, 31 to 75 ms) than in MI control subjects (110+/-24 ms; range, 78 to 179 ms, P<.001) or the normal control subjects (123+/-38 ms, P<.001), but the SD of the instantaneous beat-to-beat variability (SD1) did not differ between the groups. The complex plots were caused by periods of alternating sinus intervals, resulting in an increased SD1/SD2 ratio in the VT group. This ratio increased during the 1-hour preceding the onset of 27 spontaneous VT episodes (0.43+/-0.20) compared with the 24-hour average ratio (0.33+/-0.19) (P<.01).

CONCLUSIONS

Reduced long-term RR-interval variability, associated with episodes of beta-to-beat sinus alternans, is a highly specific sign of a propensity for spontaneous onset of VT, suggesting that abnormal beat-to-beat heart-rate dynamics may reflect a transient electrical instability favoring the onset of VT in patients conditioned by structurally abnormal hearts.

Parenteral antiarrhythmics for life-threatening ventricular arrhythmias

The acute management of life-threatening ventricular tachyarrhythmias often includes the use of parenteral antiarrhythmics. There are a number of agents currently available for this purpose. They are used to suppress inducible monomorphic ventricular tachycardia during programmed electrical stimulation, they terminate spontaneous sustained ventricular tachycardia, and prevent ventricular fibrillation in the setting of an acute myocardial infarction. Serious adverse reactions include proarrhythmia, hypotension, severe bradyarrhythmias, and precipitation of congestive heart failure. A comparative evaluation of intravenous antiarrhythmics is difficult due to inherent differences in the choice of agents for study, protocol design, patient population, defined endpoint, and serum drug levels. Likewise, the reported adverse reaction rates vary from 0.4% to 75%. To understand the difficulties in clinical decision-making in this problem area, particularly drug selection, we present here a review of pertinent clinical trials evaluating parenteral drug efficacy and adverse effects.

Dispersion of QT interval in patients with and without susceptibility to ventricular tachyarrhythmias after previous myocardial infarction

OBJECTIVES

The aim of this study was to estimate the value of QT dispersion measurement from the standard 12-lead electrocardiogram (ECG) in identifying patients susceptible to reentrant ventricular tachyarrhythmias after a previous myocardial infarction.

BACKGROUND

Variability in QT interval duration on the different leads of the 12-lead ECG has been proposed as an indicator of risk for ventricular arrhythmias in different clinical settings, but the value of QT dispersion measurement in identifying patients at risk for reentrant ventricular tachyarrhythmias after myocardial infarction is not known.

METHODS

The QT interval duration, QT dispersion and clinical and angiographic variables were compared between 30 healthy subjects; 40 patients with a previous myocardial infarction but no history of arrhythmic events or inducible ventricular tachycardia during programmed electrical stimulation; and 30 postinfarction patients with a history of cardiac arrest (n = 12) or sustained ventricular tachycardia (n = 18) and inducible, sustained monomorphic ventricular tachycardia by electrical stimulation.

RESULTS

Dispersion of the corrected QT interval (QTc) differed significantly between the study groups and was significantly increased in patients with susceptibility to ventricular tachyarrhythmias ([mean +/- SD] 104 +/- 41 ms) compared with that in both healthy subjects (38 +/- 14 ms, p < 0.001) and postinfarction patients with no susceptibility to arrhythmias (65 +/- 31 ms, p < 0.001). Maximal QT interval duration was also prolonged in the group with arrhythmias compared with that in the other groups (p < 0.001). Multivariate analysis, including clinical and angiographic variables, QT dispersion and maximal QT interval, showed that QT dispersion was the independent factor that most effectively identified the patient groups with and without susceptibility to ventricular tachyarrhythmias (p < 0.001).

CONCLUSIONS

Increased QT dispersion is related to susceptibility to reentrant ventricular tachyarrhythmias, independent of degree of left ventricular dysfunction or clinical characteristics of the patient, suggesting that the simple, noninvasive measurement of this interval from a standard 12-lead ECG makes a significant contribution to identifying patients at risk for life-threatening arrhythmias after a previous myocardial infarction.

Impaired low-frequency oscillations of heart rate in patients with prior acute myocardial infarction and life-threatening arrhythmias

Myocardial infarction results in abnormal cardiac autonomic function, which carries an increased risk of cardiac mortality, but it is not well known whether autonomic dysfunction itself predisposes patients to life-threatening arrhythmias or whether it merely reflects the severity of underlying ischemic heart disease. To determine the significance of abnormalities of cardiovascular neural regulation on the risk for ventricular tachycardia (VT), heart rate (HR) variability in the time and frequency domain were compared in a case-control study between 30 patients with a prior myocardial infarction and a history of sustained VT (n = 18) or cardiac arrest (n = 12) (VT group) and 30 patients with a prior myocardial infarction but no arrhythmic events (control group). The patient groups were carefully matched with respect to age, sex, location, ejection fraction, number of prior infarctions, number of diseased coronary arteries, and beta-blocking medication. In all patients in the VT group, inducibility into sustained VT was achieved, but none of the control patients had inducible nonsustained or sustained VT during programmed electrical stimulation. Patients in the VT group had a significantly lower SD of the RR intervals (p < 0.01), and reduced ultra low-, very low-, and low-frequency power spectral components of HR variability (p < 0.001 for all) than controls, but the high-frequency component of HR variability did not differ significantly between groups. In multiple regression analysis, reduced very low-frequency power of HR variability was the strongest independent predictor of VT susceptibility.(ABSTRACT TRUNCATED AT 250 WORDS)

Relation between heart rate variability and spontaneous and induced ventricular arrhythmias in patients with coronary artery disease

OBJECTIVES

The aim of this study was to determine the relation between autonomic control of heart rate and the spontaneous occurrence and inducibility of ventricular arrhythmias in patients with coronary artery disease.

BACKGROUND

Low heart rate variability increases the risk of arrhythmic events. It is not known whether impaired autonomic heart rate control reflects alterations in functional factors that contribute to the initiation of spontaneous arrhythmias or whether it is the consequence of an anatomic substrate for reentrant tachyarrhythmias.

METHODS

Fifty-four patients with coronary artery disease with a history of sustained ventricular tachycardia (n = 25) or cardiac arrest (n = 29) were studied by 24-h ambulatory electrocardiographic recording and by programmed electrical stimulation. Heart rate variability was compared among the patients with and without spontaneous ventricular arrhythmias and with and without inducibility of sustained ventricular tachyarrhythmias.

RESULTS

Eight patients had a total of 21 episodes of sustained ventricular tachycardia on Holter recordings. Standard deviation of RR intervals and low frequency and very low frequency components of heart rate variability were significantly blunted in patients with sustained ventricular tachycardias compared with those without repetitive ventricular ectopic activity (p < 0.05, p < 0.01 and p < 0.05, respectively). However, no significant alterations were observed in heart rate variability before the onset of 21 episodes of sustained ventricular tachycardia. Heart rate variability did not differ between the patients with or without nonsustained episodes of ventricular tachycardia. In patients with frequent ventricular ectopic activity, low frequency and very low frequency power components were significantly blunted compared with those with infrequent ventricular ectopic activity (p < 0.01 and p < 0.001, respectively). Heart rate variability did not differ significantly between the patients with and without inducible sustained ventricular tachyarrhythmias.

CONCLUSIONS

Impaired very low and low frequency oscillation of heart rate reflects susceptibility to the spontaneous occurrence of ventricular arrhythmias but may not reflect the instantaneous triggers for life-threatening arrhythmias or a specific marker of the arrhythmic substrate for ventricular tachyarrhythmias.

Beta-blocker therapy in the Cardiac Arrhythmia Suppression Trial. CAST Investigators

The Cardiac Arrhythmia Suppression Trial (CAST) showed antiarrhythmic drug suppression of asymptomatic or mildly symptomatic ventricular arrhythmias in survivors of myocardial infarction to be harmful. This study retrospectively searched the CAST results for evidence of mortality and morbidity reduction in patients receiving optional beta-blocker therapy. All enrolled (n = 2,611) and suppressed main study (n = 1,735) CAST patients with an ejection fraction of < or = 40% were examined using univariate analysis, Kaplan-Meier curves, and a Cox proportional-hazards multivariate analysis with respect to optional beta-blocker therapy prescribed at baseline. CAST patients receiving beta-blocker therapy had significantly enhanced survival at 30 days, and at 1 and 2 years of follow-up against all-cause and arrhythmic death or nonfatal cardiac arrest. Multivariate analysis showed beta-blocker therapy to be independently associated with a one-third reduction in arrhythmic death or cardiac arrest (p = 0.036). In CAST patients with a history of congestive heart failure, beta-blocker therapy was independently associated with longer time to occurrence of new or worsened congestive heart failure (p = 0.015). This study supports the secondary preventive benefit of beta-blocker therapy in high-risk post-myocardial infarction patients, and calls attention to the possible preventive benefit of beta-blocker therapy against proarrhythmic events experienced in the CAST.

Empiric therapy with beta-blockers

The only class of drugs with significant effects on ventricular fibrillation and sudden death in humans is that of beta-blockers. The exact mechanisms for these prophylactic effects are not known but may be related to both antiischemic or antiarrhythmic influences. It seems reasonable to suggest that one should use a beta-blocker with proven effect on total mortality and sudden cardiac death after myocardial infarction as prophylaxis. Therefore, propranolol, timolol, or metoprolol, should be instituted in order to improve prognosis when there are no contraindications. In addition to possible effects on survival one would also expect to reduce the risk for new ischemic events with angina or reinfarction. In contrast, class I antiarrhythmic agents are useful for symptomatic ventricular arrhythmias but there is no proof for any effect on ventricular fibrillation and sudden cardiac death.

Effectiveness of propranolol added to a type I antiarrhythmic agent for sustained ventricular tachycardia secondary to coronary artery disease

The effect of adding propranolol to procainamide, quinidine, propafenone or disopyramide was prospectively evaluated in 37 patients, all with prior infarction and inducible ventricular tachycardia (VT). After showing that VT remained inducible during therapy with a type I drug, 23 patients received intravenous propranolol. The ventricular effective refractory period, prolonged by the type I agent, was further increased by propranolol. The cycle length of the VT also increased after the type I drug and propranolol exaggerated this effect. Seven of the 23 patients were rendered noninducible after propranolol and another 10 manifested a greater than 100 ms increase in induced VT cycle length. In the other 14 patients, propranolol was infused immediately after the basal study. If VT remained inducible, testing was repeated after a type I drug was added. The ventricular effective refractory period, as well as the VT cycle length, increased after propranolol and was further prolonged after the addition of a type I agent. Seven of these 14 patients were rendered noninducible, 3 with propranolol alone and 4 others with the combination, and in 4, the VT cycle length was prolonged by greater than 100 ms. A total of 17 patients were discharged on either propranolol alone (3 patients) or on an effective combination (14 patients). During a mean follow-up of 20 months, 1 patient died suddenly, 2 had recurrence of well-tolerated VT and 9 remain on therapy. Thus, propranolol has a demonstrable antiarrhythmic effect in the invasive laboratory and may supplement the antiarrhythmic efficacy of conventional type I antiarrhythmic drugs.