A prospective comparison of triple extrastimuli and left ventricular stimulation in studies of ventricular tachycardia induction

Programmed Ventricular Stimulation: Risk Stratification and Guiding Antiarrhythmic Therapies

Electrophysiologic testing with programmed ventricular stimulation (PVS) has been utilized to induce ventricular tachycardia (VT), thereby improving risk stratification for patients with ischemic and nonischemic cardiomyopathies and determining the effectiveness of antiarrhythmic therapies, especially catheter ablation. A variety of procedural aspects can be modified during PVS in order to alter the sensitivity and specificity of the test including the addition of multiple baseline pacing cycle lengths, extrastimuli, and pacing locations. The definition of a positive result is also critically important, which has varied from exclusively sustained monomorphic VT (>30 seconds) to any ventricular arrhythmia regardless of morphology. In this review, we discuss the history of PVS and evaluate its role in sudden cardiac death risk stratification in a variety of patient populations. We propose an approach to future investigations that will capitalize on the unique ability to vary the sensitivity and specificity of this test. We then discuss the application of PVS during and following catheter ablation. The strategies that have been utilized to improve the efficacy of intraprocedural PVS are highlighted during a discussion of the limitations of this probabilistic strategy. The role of noninvasive programmed stimulation is also reviewed in predicting recurrent VT and informing management decisions including repeat ablations, modifications in antiarrhythmic drugs, and implantable cardioverter-defibrillator programming. Based on the available evidence and guidelines, we propose an approach to future investigations that will allow clinicians to optimize the use of PVS for risk stratification and assessment of therapeutic efficacy.

Electrophysiology testing for risk stratification of patients with ischaemic cardiomyopathy: a call for action

Current guidelines recommendations, based on the results of primary sudden cardiac death prevention trials, use the left ventricular ejection fraction (LVEF) as a sole criterion for the indication of implantable cardioverter defibrillator therapy for primary prevention purposes. In this article, we review the sensitivity and specificity of LVEF for predicting arrhythmic vs. non-arrhythmic cardiac death and examine existing evidence on the use of electrophysiology testing for risk stratification of ischaemic patients with reduced left ventricular function.

Analytic Reviews: Electrophysiologic Testing in the Intensive Care Unit

The role of electrophysiologic concepts and procedures in managing patients with potentially life-threatening ar rhythmias in the intensive care unit is discussed. These patients may be survivors of sudden cardiac arrest or myocardial infarction or may be admitted for syncope or sustained or nonsustained ventricular tachycardia. The value of electrophysiologic testing is discussed in terms of the distinction between wide QRS complex tachycardias that are supraventricular or ventricular in origin and those in which preexcitation syndromes may be important. Drug-induced ventricular arrhythmias are discussed, with specific emphasis on torsades de pointes. Finally, the use of His bundle recordings in pa tients with atrioventricular conduction disturbances is discussed. The methodology of electrophysiologic test ing, including stimulation protocols and interpretation of results, is described.

Dynamics of propagation of premature impulses in structurally remodeled infarcted myocardium: a computational analysis

Initiation of cardiac arrhythmias typically follows one or more premature impulses either occurring spontaneously or applied externally. In this study, we characterize the dynamics of propagation of single (S2) and double premature impulses (S3), and the mechanisms of block of premature impulses at structural heterogeneities caused by remodeling of gap junctional conductance (Gj) in infarcted myocardium. Using a sub-cellular computer model of infarcted tissue, we found that |I_Na,max|, prematurity (coupling interval with the previous impulse), and conduction velocity (CV) of premature impulses change dynamically as they propagate away from the site of initiation. There are fundamental differences between the dynamics of propagation of S2 and S3 premature impulses: for S2 impulses |I_Na,max| recovers fast, prematurity decreases and CV increases as propagation proceeds; for S3 impulses low values of |I_Na,max| persist, prematurity could increase, and CV could decrease as impulses propagate away from the site of initiation. As a consequence it is more likely that S3 impulses block at sites of structural heterogeneities causing source/sink mismatch than S2 impulses block. Whether premature impulses block at Gj heterogeneities or not is also determined by the values of Gj (and the space constant λ) in the regions proximal and distal to the heterogeneity: when λ in the direction of propagation increases >40%, premature impulses could block. The maximum slope of CV restitution curves for S2 impulses is larger than for S3 impulses. In conclusion: (1) The dynamics of propagation of premature impulses make more likely that S3 impulses block at sites of structural heterogeneities than S2 impulses block; (2) Structural heterogeneities causing an increase in λ (or CV) of >40% could result in block of premature impulses; (3) A decrease in the maximum slope of CV restitution curves of propagating premature impulses is indicative of an increased potential for block at structural heterogeneities.

QT interval heterogeneities induced through local epicardial warming/cooling. An experimental study

INTRODUCTION AND OBJECTIVES

Abnormal QT interval durations and dispersions have been associated with increased risk of ventricular arrhythmias. The present study examines the possible arrhythmogenic effect of inducing QT interval variations through local epicardial cooling and warming.

METHODS

In 10 isolated rabbit hearts, the temperatures of epicardial regions of the left ventricle were modified in a stepwise manner (from 22°C to 42°C) with simultaneous electrogram recording in these regions and in others of the same ventricle. QT and activation-recovery intervals were determined during sinus rhythm, whereas conduction velocity and ventricular arrhythmia induction were determined during programmed stimulation.

RESULTS

In the area modified from baseline temperature (37°C), the QT (standard deviation) was prolonged with maximum hypothermia (195 [47] vs 149 [12] ms; P<.05) and shortened with hyperthermia (143 [18] vs 152 [27] ms; P<.05). The same behavior was displayed for the activation-recovery interval. The conduction velocity decreased with hypothermia and increased with hyperthermia. No changes were seen in the other unmodified area. Repetitive responses were seen in 5 experiments, but no relationship was found between their occurrence and hypothermia or hyperthermia (P>.34).

CONCLUSIONS

In the experimental model employed, local variations in the epicardial temperature modulate the QT interval, activation-recovery interval, and conduction velocity. Induction of heterogeneities did not promote ventricular arrhythmia occurrence.

β1-Adrenoceptor blocker aggravated ventricular arrhythmia

OBJECTIVES

To assess the impact of β1 -adrenoceptor blockers (β1 -blocker) and isoprenaline on the incidence of idiopathic repetitive ventricular arrhythmia that apparently decreases with preprocedural anxiety.

METHODS

From January 2010 to July 2012, six patients were identified who had idiopathic ventricular arrhythmias that apparently decreased (by greater than 90%) with preprocedural anxiety. The number of ectopic ventricular beats per hour (VPH) was calculated from Holter or telemetry monitoring to assess the ectopic burden. The mean VPH of 24 hours from Holter before admission (VPH-m) was used as baseline (100%) for normalization. β1 -Blockers, isoprenaline, and/or aminophylline were administrated successively on the ward and catheter lab to evaluate their effects on the ventricular arrhythmias.

RESULTS

Among 97 consecutive patients with idiopathic ventricular arrhythmias, six had reduction in normalized VPHs in the hour before the scheduled procedure time from (104.6 ± 4.6%) to (2.8 ± 1.6%) possibly due to preprocedural anxiety (P < 0.05), then increased to (97.9 ± 9.7%) during β1 -blocker administration (P < 0.05), then quickly reduced to (1.6 ± 1.0%) during subsequent isoprenaline infusion. Repeated β1 -blocker quickly counteracted the inhibitory effect of isoprenaline, and VPHs increased to (120.9 ± 2.4%) from (1.6 ± 1.0%; P < 0.05). Isoprenaline and β1 -blocker showed similar effects on the arrhythmias in catheter lab.

CONCLUSIONS

In some patients with structurally normal heart and ventricular arrhythmias there is a marked reduction of arrhythmias associated with preprocedural anxiety. These patients exhibit a reproducible sequence of β1 -blocker aggravation and catecholamine inhibition of ventricular arrhythmias, including both repetitive ventricular premature beats and monomorphic ventricular tachycardia.

[Limits and scopes of invasive risk stratification. Do we still need programmed ventricular stimulation?]

Patients with ischemic heart disease and left ventricular systolic dysfunction (ICM), dilated (DCM), hypertrophic (HCM), or arrhythmogenic right ventricular cardiomyopathy (ARVCM) carry a high risk of sudden cardiac death (SCD). Ventricular tachyarrhythmias are most often the cause of SCD, which can be treated with internal cardioverter defibrillators (ICDs). However, a great proportion of these high-risk patients will never experience potentially lethal ventricular arrhythmias, and as such will never be in need of these devices. Given the risks, inconvenience, and costs of ICDs, markers that adequately stratify patients according to their risk of SCD are needed. Programmed ventricular stimulation (PVS) has long been used to identify the patients' risk of SCD. However, the prognostic ability of PVS is only modest and the negative predictive value is poor. As far as patients with ICM are concerned, recent data from the MUSTT and MADIT II trials demonstrate that in patients with a left ventricular ejection fraction between 30% and 40%, inducibility by PVS can help to identify patients who are at particularly increased risk of SCD. The value of PVS in patients with DCM, HCM, and ARVCM for risk stratification of SCD is less clear and the available data even more limited. In these patients, the inducibility of ventricular tachyarrhythmias does not clearly correlate with VT/VF (ventricular tachycardia/ventricular fibrillation) risk, and more importantly, noninducibility does not portend good prognosis. The current German guidelines appreciate these uncertainties of PVS for risk stratification with class IIb recommendations in certain patients with ICM, HCM or ARVCM. In the future, combining the results of invasive PVS with other noninvasive parameters may improve its prognostic value. Furthermore, expanding the role of PVS to guiding therapeutic ablation of ventricular arrhythmias may influence patient's future risk of SCD.

Tissue sodium concentration in myocardial infarction in humans: a quantitative 23Na MR imaging study

PURPOSE

To prospectively determine whether the absolute tissue sodium concentration (TSC) increases in myocardial infarctions (MIs) in humans and whether TSC is related to infarct size, infarct age, ventricular dysfunction, and/or electrophysiologic inducibility of ventricular arrhythmias.

MATERIALS AND METHODS

Delayed contrast material-enhanced 1.5-T hydrogen 1 ((1)H) magnetic resonance (MR) imaging was used to measure the size and location of nonacute MIs in 20 patients (18 men, two women; mean age, 63 years +/- 9 [standard deviation]; age range, 48-82 years) examined at least 90 days after MI. End-systolic and end-diastolic volumes, ejection fraction, and left ventricle (LV) mass were measured with cine MR imaging. The TSC in normal, infarcted, and adjacent myocardial tissue was measured on sodium 23 ((23)Na) MR images coregistered with delayed contrast-enhanced (1)H MR images. Programmed electric stimulation to induce monomorphic ventricular tachycardia (MVT) was used to assess arrhythmic potential, and myocardial TSC was compared between the inducible MVT and noninducible MVT patient groups.

RESULTS

The mean TSC for MIs (59 micromol/g wet weight +/- 10) was 30% higher than that for noninfarcted (remote) LV regions (45 micromol/g wet weight +/- 5, P < .001) and that for healthy control subjects, and TSC did not correlate with infarct age or functional and morphologic indices. The mean TSC for tissue adjacent to the MI (50 micromol/g wet weight +/- 6) was intermediate between that for the MI and that for remote regions. The elevated TSC measured in the MI at (23)Na MR imaging lacked sufficient contrast and spatial resolution for routine visualization of MI. Cardiac TSC did not enable differentiation between patients in whom MVT was inducible and those in whom it was not.

CONCLUSION

Absolute TSC is measurable with (23)Na MR imaging and is significantly elevated in human MI; however, TSC increase is not related to infarct age, infarct size, or global ventricular function. In regions adjacent to the MI, TSC is slightly increased but not to levels in the MI.

Determinants of inducibility of ventricular tachycardia

We analyzed the incidence and predictive factors for induction of clinical ventricular tachycardia (VT) during an electrophysiologic study in 127 patients with structural heart disease and spontaneous VT documented by 12-lead electrocardiography. Eighty-five patients had coronary artery disease (CAD), 24 had idiopathic dilated cardiomyopathy (IDC), and 18 had right ventricular dysplasia (RVD). Clinical variables were age, gender, electrocardiographic patterns of spontaneous arrhythmia, cardiac diagnosis, left ventricular (LV) ejection fraction (EF), infarct location, and presence of LV aneurysm. Clinical VT was induced in 76 patients (60%, group 1) and was not induced in 51 patients (group 2). Clinical VT was induced in 83% of patients with RVD, 58% of patients with CAD, and 50% of patients with IDC (p = 0.07). LVEF tended to be significantly higher in group 1 than in group 2 (p = 0.06). The presence of left QRS axis in the frontal plane during spontaneous VT was significantly associated with a higher inducibility both in the general group (69% vs 46%, p <0.02) and in patients with CAD (70% vs 44%, p <0.02). In patients with CAD, only the presence of a left QRS axis was significantly associated with a higher inducibility. A multivariate analysis identified only the left QRS axis as a significant and independent predictor of induction of clinical VT. The association of a leftward axis with inducibility suggests that vectorial factors in the depolarization wavefronts may be related to inducibility since conventional stimulation is performed from the right ventricle, producing a leftward axis in most cases.

Lack of benefit of very short basic drive train cycle length or repetition of extrastimulus coupling intervals for induction of ventricular tachycardia

INTRODUCTION

There are considerable variations of uncertain importance in basic drive train cycle lengths and degree of repetition of extrastimuli used in programmed ventricular stimulation protocols in different laboratories. We compare prospectively three different stimulation protocols to examine the influence of a short basic drive train cycle length and repetition of extrastimuli on induction of ventricular tachycardia.

METHODS AND RESULTS

Thirty consecutive patients who had documented ventricular tachycardia or fibrillation based on underlying coronary artery disease underwent programmed ventricular stimulation with each of the three study protocols. Protocol A used a basic drive train cycle length of 400 msec with each extrastimulus coupling interval delivered only once. Protocol B used the same basic drive train cycle length, but with each extrastimulus coupling interval repeated three times before decrementing. Protocol C used 300 msec as the cycle length of basic drive trains without repetition of extrastimuli. Sixty-three percent, 67%, and 63% of the study patients had ventricular tachycardia inducible with protocols A, B, and C, respectively (P = NS). Ventricular fibrillation was induced in 23% of the 30 patients in all three protocols. There were no significant differences in the mean cycle lengths of induced ventricular tachycardia, the number of extrastimuli used, and the coupling interval of the last extrastimulus inducing ventricular tachycardia among the three protocols.

CONCLUSION

This study showed no clinical benefit for repetition of extrastimuli that have failed to induce a ventricular tachyarrhythmia during programmed ventricular stimulation. A short basic cycle length of 300 msec was not superior to 400 msec for induction of ventricular tachyarrhythmias. We recommend the use of basic cycle length 400 msec with delivery of each extrastimulus interval only once as the initial protocol for programmed ventricular stimulation.

Long-term results of electrophysiologically guided sotalol therapy for life-threatening ventricular arrhythmias

The efficacy and safety of sotalol therapy for ventricular arrhythmias was evaluated in 133 patients with drug-refractory ventricular arrhythmias. All patients had baseline electrophysiologic studies before and after oral sotalol therapy. Sixty-six patients were discharged home, treated with sotalol (52 patients without inducible ventricular tachycardia or fibrillation and 14 patients with hemodynamically stable inducible ventricular tachycardia). The mean follow-up period was 41 +/- 27 months for the 14 patients with hemodynamically stable ventricular tachycardia. Sotalol was effective in 8 of these 14 patients. Recurrent nonlethal ventricular tachycardia occurred in 3 patients; 2 patients had sudden death; and 1 patient had adverse side effects. The 52 patients without inducible ventricular tachycardia were followed up for a mean period of 36 +/- 30 months. Thirty-five of 52 patients were successfully treated. Two patients had recurrent ventricular tachycardia; both of these episodes of ventricular tachycardia occurred within the first year. Four patients had sudden cardiac death; three of these deaths occurred within the first month, and the last episode of sudden death occurred after 8 years of sotalol therapy. The actuarial incidence of sotalol efficacy was 76% at 1 year, 72% at 2 years, 64% at 4 years, and 52% at 5 years. Approximately 46% of patients receiving long-term sotalol treatment reported side effects. Side effects severe enough to warrant withdrawal of sotalol occurred in 7 (11%) patients. The results of our study suggest that sotalol is effective for selected patients with drug refractory ventricular arrhythmias. Although the incidence of side effects are high, patients appear to tolerate long-term sotalol therapy well.

Insights into the Electrophysiology Study Versus Electrocardiographic Monitoring Trial: its programmed stimulation protocol may introduce bias when assessing long-term antiarrhythmic drug therapy

OBJECTIVES

We hypothesized that if the Electrophysiology Study Versus Electrocardiographic Monitoring (ESVEM) trial programmed stimulation protocol misclassified some drug trials as effective, then the misclassification rate would be proportionally greater for drugs other than sotalol.

BACKGROUND

In the ESVEM trial, patients treated with sotalol had fewer arrhythmic recurrences than those treated with other antiarrhythmic drugs despite similar efficacy predictions during electrophysiologic testing.

METHODS

We retrospectively compared the standard programmed stimulation protocol used at Case Western Reserve University, which used three extrastimuli during all follow-up studies, with the ESVEM protocol in 176 antiarrhythmic drug trials: sotalol (n = 54), procainamide (n = 73) and quinidine/mexiletine (n = 49).

RESULTS

Predictions of efficacy were higher in the sotalol trials (14 of 54 standard, 20 of 54 ESVEM) than in procainamide trials (7 of 73 standard, 14 of 73 ESVEM) or quinidine/mexiletine trials (1 of 49 standard, 7 of 49 ESVEM). Thus, the two protocols classified 19 of 176 trials differently: not effective by the standard protocol but effective by the ESVEM trial. Discordant predictions of drug efficacy constituted a smaller proportion of ESVEM protocol efficacy predictions for sotalol (6 [30%] of 20) than for the other drugs (13 [62%] of 21, p < or = 0.05).

CONCLUSIONS

In the present study, the ESVEM programmed stimulation protocol predicted efficacy more often than the standard protocol. Discordant predictions represented a smaller portion of efficacy predictions for sotalol than for the other drugs. Thus, in the ESVEM trial, the superior long-term follow-up observed in patients assigned to sotalol may have been an artifact of the stimulation protocol utilized by the ESVEM investigators.

Programmed ventricular stimulation using tandem versus simple sequential protocols

The objective was to determine whether two commonly used ventricular stimulation protocols, one more complex than the other, produced concordant results. If such were the case, the simpler protocol would streamline activities in clinical electrophysiology laboratories.

BACKGROUND

Two programmed ventricular stimulation protocols were compared. (1) With the tandem method, the first extrastimulus (S2) is moved stepwise to the effective refractory period and then moved out 50 msec; the second extrastimulus (S3) is then decremented until it fails to capture; S2 and S3 are then decremented in a semialternating (tandem) fashion so that both continue to capture. When S2 reaches the refractory period + 10 msec and S3 fails to capture, S3 is then moved out 50 msec, and S4 is decremented as described for S3. (2) With the simple sequential method, the first extrastimulus (S2) is decremented stepwise to the refractory period, and then moved out 10 msec to assure capture; S3 is then similarly decremented to the refractory period and then moved out 10 msec; and S4 is then similarly decremented.

METHODS

This was a prospective, randomized, crossover, consecutive series study. Both protocols were tested in each patient on the same day in randomized order.

RESULTS

There were 84 matched studies. Fifty-six patients provided data from baseline electrophysiological studies, and 28 of these provided additional data during drug trials. There was a 93% concordance between the two methods, including the primary outcomes of inducibility of clinical arrhythmias, inducibility of nonclinical arrhythmias, and noninducibility (P < 0.001). Discordances were few and evenly distributed between the two protocols (P = NS). Results were similar for baseline studies and drug trials. The simple sequential method required less time to perform (P < or = 0.01).

CONCLUSIONS

Tandem and simple sequential protocols provide concordant results. No advantage could be demonstrated for the more complex tandem method.

Comparison of number of extrastimuli versus change in basic cycle length for induction of ventricular tachycardia by programmed ventricular stimulation

OBJECTIVES

The purpose of this study was to examine the effects of varying basic cycle lengths in a programmed stimulation protocol if up to seven extrastimuli were available at each basic cycle length.

BACKGROUND

There is no uniformly accepted protocol for induction of ventricular tachycardia. Most protocols limit the number of extrastimuli to two or three but use several basic cycle lengths.

METHODS

Twenty-eight patients with coronary artery disease and documented spontaneous sustained ventricular tachycardia or ventricular fibrillation were studied. In the absence of antiarrhythmic drugs, each patient underwent three inductions of ventricular tachycardia/ventricular fibrillation using sinus rhythm or right ventricular pacing at 600 or 400 ms as the basic cycle length. Up to seven extrastimuli were allowed at each basic cycle length.

RESULTS

The maximal yield of clinical tachycardia (96%) was identical for each basic cycle length and was achieved using a maximum of seven, five and four extrastimuli for sinus rhythm and 600 and 400 ms, respectively. A basic cycle length of 400 ms required fewer extrastimuli (2.4 +/- 0.7) to induce ventricular tachycardia/ventricular fibrillation than did 600 ms (2.7 +/- 1.1, p = 0.014) or sinus rhythm (3.4 +/- 1.2, p < 0.001). There was no significant difference in the cycle lengths of the induced ventricular tachycardia, incidence of induced ventricular fibrillation or requirement for direct current countershock.

CONCLUSIONS

The use of an adequate number of extrastimuli obviates the need for multiple basic cycle lengths for induction of ventricular tachycardia and does not increase induction of unwanted ventricular fibrillation. If only one basic cycle length is used, the ease of inducibility can be quantified in terms of the number of extrastimuli required. Fewer extrastimuli were required for induction of ventricular tachycardia if a basic cycle length of 400 ms was used. These data favor the use of ventricular pacing at a basic cycle length of 400 ms with up to at least four extrastimuli as the standard stimulation protocol for induction of ventricular tachycardia.

Management of nonsustained ventricular tachycardia guided by electrophysiological testing

Two hundred eighty patients with spontaneous nonsustained ventricular tachycardia were treated based on the results of electrophysiological testing. Seventy-nine patients had no evidence of structural heart disease, 134 had coronary artery disease, 43 had idiopathic dilated cardiomyopathy, and 24 patients had miscellaneous types of heart disease. Sustained monomorphic ventricular tachycardia was induced during electrophysiological testing in the drug free state in 52 of 280 patients (19%). Ventricular tachycardia was induced more frequently in patients with coronary artery disease (32%) than in any of the other groups (P < 0.001). The patients with inducible sustained monomorphic ventricular tachycardia underwent a mean of 1.9 +/- 1.3 drug trials. Twenty-five patients had the induction of ventricular tachycardia suppressed by pharmacological therapy and were treated with the drug judged to be effective during electropharmacological testing. Twenty-seven patients continued to have inducible sustained monomorphic ventricular tachycardia despite antiarrhythmic therapy and were discharged on the drug that made induced ventricular tachycardia best tolerated. Forty-five of 280 patients (16.1%) died during a mean follow-up period of 19.6 +/- 14.4 months. There were 15 sudden cardiac deaths, 21 nonsudden cardiac deaths, 6 noncardiac deaths, and 3 deaths that could not be classified. Sudden cardiac death mortality was lowest in the patients without structural heart disease (0% at 2 years), intermediate in the patients with coronary artery disease and miscellaneous heart disease (4% at 2 years), and highest in the patients with idiopathic dilated cardiomyopathy (13% at 2 years; P < 0.01 for pairwise comparisons). No patient treated with a drug that had suppressed the induction of sustained ventricular tachycardia died suddenly during the follow-up period whereas four of 27 patients who were discharged on "ineffective antiarrhythmic drugs" and 11 of 228 patients without inducible sustained ventricular tachycardia experienced sudden cardiac death during the follow-up period. By multivariate analysis, ejection fraction and inducible ventricular tachycardia during the predischarge electrophysiological test were independent predictors of sudden cardiac death. In conclusion, in patients with spontaneous non-sustained ventricular tachycardia: (1) Arrhythmia inducibility varies depending on the underlying heart disease.(ABSTRACT TRUNCATED AT 400 WORDS)

Programmed electrical stimulation protocols: variations on a theme

A series of prospective protocols were designed to determine the yield ratio (true positives vs. false positives = nonclinical) in various patient groups using a variety of programmed electrical stimulation (PES) variables. First, a PES protocol was used in 772 patients. Single, double, and triple extrastimuli were delivered in sequence (leaving each successive extrastimulus just beyond its refractory period before moving to the next extrastimulus) during sinus rhythm and two ventricular paced rates at the RV apex, before moving to the outflow tract and repeating the sequence and then moving on to isoproterenol infusion with the PES sequence repeated at the apex. This protocol met NASPE standards for induction of VT in patients with coronary artery disease and a history of VT, while failing to induce monomorphic VT in any control patient. The best yield ratios combined with the greatest likelihood of inducing clinical tachycardia were achieved with sinus rhythm and three extrastimuli, and pacing at the lower rate and three extrastimuli. Pacing at the faster rate and triple extrastimuli was highly inductive of clinical arrhythmias, but had a low yield ratio due to induction of more nonclinical arrhythmias than other steps. The next protocol was performed in 61 patients with inducible ventricular tachycardia. In each case, the protocol described above was completed at the RV apex, even if tachycardia was also induced at an earlier point in the protocol. This allowed for more accurate yield ratios to be established for each step in the protocol, since each patient was exposed to each of these steps.(ABSTRACT TRUNCATED AT 250 WORDS)

Recordings from the slow zone of reentry during burst pacing versus programmed premature stimulation for initiation of reentrant ventricular tachycardia in patients with coronary artery disease

Programmed premature stimulation and burst pacing were compared for initiation of ventricular tachycardia (VT) in 16 patients with inducible sustained monomorphic VT. In all patients VT could be induced by programmed stimulation with 2 or 3 extrastimuli. On the other hand, initiation of VT by burst pacing was dependent on the length of the train; only 2 to 4 of the 11 trains tested could induce VT in any single patient. Recordings obtained from the slow zone of reentry showed that programmed premature stimulation that induced VT resulted in a critical degree of conduction delay as revealed by lengthening of local fractionated electrograms spanning 70 to 100% of the diastolic interval. Similarly, the last beat of a burst pacing train that induced VT was always followed by a similar degree of local conduction delay, whereas trains that failed to induce VT were followed by a lesser delay. It is concluded that although programmed stimulation with up to 3 extrastimuli was consistently successful in inducing VT, burst pacing succeeded in only 26% of the trials and was dependent on the length of the train, which varied from one patient to the other. Similar to what was shown previously in the experimental model of reentrant VT, burst pacing could initiate, conceal, terminate, and reinitiate reentry depending on the length of the train.

Stimulation hierarchy: optimal sequence for double and triple extrastimuli during electrophysiological studies

To determine the optimal ventricular stimulation sequence, an 11-step programmed electrical stimulation (PES) protocol was completed, even if a ventricular arrhythmia (VA) was induced with earlier steps. The protocol consisted of one, two, and three extrastimuli during sinus rhythm (SR), and at two drive pacing rates (VP1 and VP2) plus rapid burst and ramp pacing. By analyzing the 79 completed protocols that induced the clinical arrhythmia, the following were determined: (1) the frequency of induced clinical and nonclinical VA with each stimulation step; (2) the yield ratio (YR) of each step, defined as the probability of inducing clinical versus nonclinical arrhythmia; (3) the cumulative yield of induced clinical and nonclinical arrhythmia with two widely used stimulation sequences, i.e., triple extrastimuli delivered early in the stimulation protocol (MMC sequence) and triple extrastimuli delayed until after double extrastimuli failed to induce the clinical arrhythmia (B sequence); (4) the relative efficiency of these sequences were determined. The percentage of induced clinical and nonclinical arrhythmia with SR + 3 extrastimuli, VP1 + 2 extrastimuli, and VP2 + 2 extrastimuli were (53%, 5%), (36%, 5%), and (41%, 9%), respectively. The cumulative yield of induced clinical VA with the MMC-type sequence reached 55% by the third step of the protocol, whereas 50% was attained only at the eighth step of the B-type sequence. The cumulative percentage of induced nonclinical VA with either sequence was similar during the early steps of the protocol. The MMC sequence was more efficient, requiring overall 36% of potential steps for clinical arrhythmia induction, compared with 48% for the B sequence (P less than 0.001). For questionable arrhythmia states, e.g., syncope of unknown origin and nonsustained VT, a modified sequence is proposed that may further reduce the induction of uninterpretable arrhythmias.

Programmed electrical stimulation of the ventricle: an efficient, sensitive, and specific protocol

A relatively simple and efficient ventricular programmed electrical stimulation (PES) protocol was developed, capable of achieving high degrees of sensitivity and specificity. In a series of 481 subjects, 1, 2, and 3 extrastimuli (ES) were used successively during sinus rhythm and ventricular pacing at two drive cycle lengths, at one or more ventricular sites, together with rapid ventricular pacing, and other maneuvers such as isoproterenol infusion. Three ES were used immediately after two ES at each drive rate, rather than returning after completion of the protocol with two ES. Using the protocol, appropriate arrhythmias could be induced in 88% of all patients with ventricular fibrillation, 84% of all patients with sustained ventricular tachycardia (91% with underlying coronary disease), and 58% of patients with severe nonsustained ventricular tachycardia. There were significant differences in inducibility between patients whose ventricular arrhythmias were due to coronary artery disease and other causes. In contrast, sustained ventricular arrhythmias (all ventricular fibrillation) could be induced in only 5% of a control group of control patients, for a specificity of 95%. The protocol described is simpler and more efficient than those that use exhaustive testing of two ES before going to three ES. Three ES during sinus rhythm proved to be the most productive step, with a higher yield ratio (true: false-positives) than two ES or three ES during pacing, especially at faster rates. Greater efficiency is also achieved by leaving the timing of an extrastimulus just beyond its effective refractory period when an additional extrastimulus is to be added, compared to protocols in which the extrastimulus is moved later in the cycle and then decremented in tandem with the additional extrastimulus. Coupling intervals less than 200 msec produced some false-positives, but fewer overall than intervals greater than or equal to 200 msec, and with yield ratios comparable to other protocol steps. The protocol described meets NASPE standards for ventricular programmed stimulation protocols, and with its demonstrated specificity and relative simplicity and efficiency may be useful as a model for groups not yet committed to an alternative protocol.

Prospective community evaluation of the signal-averaged electrocardiogram in predicting malignant ventricular arrhythmias: beneficial outcome with electrophysiology guided therapy

The role of the signal-averaged ECG was prospectively assessed in 517 patients in whom there was a suspicion for malignant ventricular arrhythmias. Patients were divided into Group I with a normal surface QRS width less than 120 ms (426 patients) and Group II with a prolonged QRS duration greater than or equal to 120 ms (91 patients). Late potentials were present in 42 (10%) Group I patients and in 24 (26%) Group II patients. Programmed ventricular stimulation was performed for standard indications in 55 patients without late potentials and in 42 patients with late potentials, combining both groups. The sudden death or recurrent sustained ventricular tachycardia rate in follow-up was evaluated based on the presence or absence of late potentials and whether programmed ventricular stimulation was performed. In the patients without late potentials, these rates were 4 patients (1.0%) in the no EP group and 3 patients (5.5%) in the EP group (p less than .05), respectively (overall 1.6%). In the patients with late potentials, these rates were 7 patients (29%) in the no EP group and 7 patients (17%) in the EP group (p = .19), respectively (overall 21%). In addition, appropriate automatic defibrillator shocks were present in 1 patient without late potentials and in 8 patients with late potentials which were not included in the recurrent sudden death or sustained ventricular tachycardia statistics. The signal-averaged ECG accurately defines patients at a higher risk for malignant ventricular arrhythmias regardless of unfiltered QRS duration.(ABSTRACT TRUNCATED AT 250 WORDS)

Routine programmed electrical stimulation in survivors of acute myocardial infarction for prediction of spontaneous ventricular tachyarrhythmias during follow-up: results, optimal stimulation protocol and cost-effective screening

Of 3,286 consecutive patients treated for acute myocardial infarction, electrophysiologic testing was performed in 1,209 survivors (37%) free of significant complications at the time of hospital discharge to determine their risk of spontaneous ventricular tachyarrhythmias during follow-up. Sustained monomorphic ventricular tachycardia was inducible by programmed electrical stimulation in 75 (6.2%). Antiarrhythmic therapy was not routinely prescribed regardless of the test results. During the 1st year of follow-up, 14 infarct survivors (19%) with inducible ventricular tachycardia experienced spontaneous ventricular tachycardia or fibrillation in the absence of new ischemia compared with 34 (2.9%) of those without inducible ventricular tachycardia (p less than 0.0005). During the extended follow-up period (median 28 months) of those with inducible ventricular tachycardia, 19 (25%) had a spontaneous electrical event; 37% of these first events were fatal. These results suggest that the most cost-effective strategy for predicting arrhythmia will be obtained by restricting electrophysiologic testing to infarct survivors whose left ventricular ejection fraction is less than 40% and using a stimulation protocol containing four extrastimuli. Electrophysiologic testing is the single best predictor of spontaneous ventricular tachyarrhythmias during follow-up in infarct survivors. The majority (94%) with a negative test benefit from the more reliable reassurance that all is well, whereas the 25% risk of electrical events in those with inducible ventricular tachycardia justifies a prospective trial of effective prophylactic antiarrhythmic interventions.

Electrophysiologic and anatomic characteristics of ventricular tachycardia induced at the right ventricular outflow tract but not at the apex

The site of ventricular stimulation is an important variable in the initiation of ventricular tachycardia (VT) by programmed ventricular stimulation. Among 169 patients studied consecutively, 17 (10%) had ventricular tachycardia induced by programmed electrical stimulation from the right ventricular outflow tract but not from the apex. Fourteen of these 17 patients had had prior myocardial infarction (12 had inferior, and two had both inferior and anterior myocardial infarction), two had a dilated cardiomyopathy, and one had a localized cardiomyopathy. Fourteen patients had echocardiograms suitable for analysis. Of these, 12 had posterior/inferior ventricular wall motion abnormalities located at the base of the heart. The ventricular effective refractory periods from the right ventricular outflow tract and right ventricular apex were 237 +/- 4 and 244 +/- 5 msec, respectively (p less than 0.05, mean +/- SEM). Induced VT had a cycle length of 229 +/- 4 msec and had the morphology of right bundle branch block in 12 patients, of left bundle branch block in three patients, and had both morphologies in two patients. In 14 patients the axis was superior. VT was initiated with two extrastimuli in 15 patients and with burst right ventricular pacing in two patients. Similar pacing techniques with identical pacing intervals did not induce VT at the right ventricular apex in 14 of these 17 patients. Further, among the 15 patients whose VT was induced at the right ventricular outflow tract with two extrastimuli, neither burst pacing (n = 13) nor two extrastimuli introduced at faster paced rates (n = 12) induced VT at the right ventricular apex.(ABSTRACT TRUNCATED AT 250 WORDS)

Observations on the initiation of sustained ventricular tachycardia by programmed stimulation

We analyzed the initiation of sustained monomorphic ventricular tachycardia (VT) by programmed ventricular stimulation (PVS) in 50 consecutive patients who had clinical VT or aborted sudden cardiac death with remote myocardial infarction. In 25 of 50 patients, the first induced QRS complex of VT was morphologically identical to the succeeding QRS complexes of VT (type I). In 25 other patients, the first VT beat had a different morphology (type II). Type I had a significantly longer VT cycle length than type II (333 +/- 65 msec and 293 +/- 66 msec, P = 0.036). Type II VT initiation required more aggressive stimulation protocol than type I (type I: type II; number of extrastimulus required for induction 2.5 +/- 0.9 : 3.0 +/- 0.6, P = 0.026; shortest extrastimuli coupling interval 244 +/- 28 msec : 220 +/- 23 msec, P = 0.002). The interval between the last extrastimulus and the onset of the first VT beat was 408 +/- 88 msec in type I and 336 +/- 75 msec in type II (P = 0.004). Furthermore, there was good correlation between the VT cycle length and the interval from last extrastimulus to the onset of nonpaced beat in type I but not in type II.(ABSTRACT TRUNCATED AT 250 WORDS)

Increasing the yield of ventricular tachycardia induction: a prospective, randomized comparative study of the standard ventricular stimulation protocol to a short-to-long protocol and a new two-site protocol

Programmed ventricular stimulation with a standard protocol that used up to three extrastimuli was compared prospectively with a short-to-long protocol and a two-site protocol in 77 consecutive patients undergoing electrophysiologic study in an attempt to increase the yield of ventricular tachycardia (VT) induction. The short-to-long protocol uses a train of eight stimuli at a short cycle length and up to two extrastimuli. The two-site protocol is similar to the standard protocol but delivers the last extrastimulus via a second spatially separated right ventricular catheter. Patients were divided into two groups based on indications for study: group 1 included 45 patients with syncope, nonsustained VT, or both, and group 2 included 32 patients with a history of sustained VT, sudden cardiac death, or both. The yield of VT induction with the short-to-long protocol was less than that with the standard protocol. In none of the patients in group 1 in whom the standard protocol results were negative did the short-to-long protocol produce sustained VT. Only two patients, both in group 2, had sustained arrhythmias induced by the short-to-long protocol when the standard protocol results were negative: one had sustained VT induced and one with long QT syndrome had ventricular fibrillation (VF) induced with the short-to-long protocol. However, the short-to-long protocol failed to induce sustained VT in seven patients in whom the standard protocol produced sustained VT. All seven of these patients required three extrastimuli with the standard protocol for induction of VT.(ABSTRACT TRUNCATED AT 250 WORDS)

Differences in QRS configuration during unipolar pacing from adjacent sites: implications for the spatial resolution of pace-mapping

To examine the spatial resolution of unipolar pace-mapping, 12 lead electrocardiograms (ECGs) recorded during pacing from each of the poles of a quadripolar catheter (5 mm interelectrode distance) were examined. Unipolar pacing was performed from each of the poles at late diastolic threshold, twice threshold and 10 mA at a cycle length of 500 ms. In 15 patients, pacing was performed at the right ventricular apex and in 14 at various left ventricular sites. Pacing from the distal catheter pole at threshold (index ECG) was used to simulate the site of origin of ventricular tachycardia, and all other ECGs were compared with the index ECG. Electrocardiograms were evaluated by two independent observers for 1) minor configuration differences (notch, new small component, change in the amplitude of individual components or change in QRS shape); 2) major differences in configuration (new large component, marked change in the amplitude of an existing component or two minor changes); and 3) peak to peak changes in amplitude. Minor differences in configuration were seen in a mean 2.4 +/- 1.9, 4.6 +/- 2.4 and 4.4 +/- 2.9 leads during pacing at 5, 10 and 15 mm from the distal electrode (index site). Major differences in configuration were seen in a mean of 0.3 +/- 0.5, 2.1 +/- 2.1 and 3.7 +/- 2.3 leads during pacing at 5, 10 and 15 mm from the index site. Differences in amplitude were seen in a mean of 3.1 +/- 2.2, 5.6 +/- 2.5 and 6.8 +/- 3.0 leads per ECG during pacing at 5, 10 and 15 mm from the index ECG pacing site, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

The long-term prognosis of patients with out-of-hospital cardiac arrest but no inducible ventricular tachycardia

The long-term prognosis of patients successfully resuscitated from cardiac arrest who do not have acute precipitating factors and in whom ventricular arrhythmias cannot be induced during baseline electrophysiologic testing is controversial. The purpose of this investigation was to evaluate the long-term risk of recurrent sudden death and determine the clinical, angiographic, hemodynamic, and electrophysiologic predictors of recurrent cardiac arrest in such patients. Twenty-six (37%) of 71 consecutive patients with a single episode of aborted sudden death did not have inducible ventricular arrhythmias (less than 7 intraventricular responses) during baseline drug-free electrophysiologic study and they form the basis of this report. Their mean age was 54 +/- 13 (mean +/- SD) years and the left ventricular ejection fraction (LVEF) was 0.47 +/- 0.17. After a mean follow-up period of 16 months, 11 patients (42%) had a recurrent cardiac arrest (fatal in 10 patients). The actuarial incidence of recurrent cardiac arrest was 30 +/- 10% at 1 year and 55 +/- 13% at 3 years. Patients with LVEF less than or equal to 0.40 had a significantly higher occurrence of recurrent cardiac arrest than those with LVEF greater than 0.40 (p = 0.02; 1-year actuarial incidence of 57 +/- 17% versus 13 +/- 19%). Patients with recurrent sudden death had a significantly greater incidence of dilated cardiomyopathy (55% versus 7%; p = 0.02) and baseline frequent premature ventricular contractions (PVCs greater than 10/hr; 64% versus 17%, p = 0.036) or nonsustained ventricular tachycardia (36% versus 0%; p = 0.37) than patients without these characteristics.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term outcome in patients who survive out of hospital ventricular fibrillation and undergo electrophysiologic studies: evaluation by electrophysiologic subgroups

The long-term outcome of 241 survivors of out of hospital ventricular fibrillation who underwent programmed electrical stimulation was evaluated. Patients were categorized according to the rhythm induced at baseline drug-free electrophysiologic testing. Ventricular fibrillation was induced in 39 patients (16%) (Group 1), sustained ventricular tachycardia in 66 patients (27%) (Group 2) and nonsustained ventricular tachycardia in 34 patients (14%) (Group 3); 102 patients (42%) (Group 4) did not have an arrhythmia inducible at baseline electrophysiologic testing. Antiarrhythmic drugs were administered over the long term to 92% of patients in Group 2, 91% of patients in Group 1 and 47% of patients in Group 4. At a mean follow-up time of 30 +/- 15 months, recurrent sudden cardiac death or nonfatal ventricular fibrillation occurred in 11 (28%) of 39 patients with inducible ventricular fibrillation (Group 1), 14 (21%) of 66 patients with inducible sustained ventricular tachycardia (Group 2), 4 (12%) of 34 patients with inducible nonsustained ventricular tachycardia (Group 3) and 16 (16%) of 102 patients without inducible arrhythmias (Group 4). Actuarial analysis revealed a 2 year cumulative arrhythmia-free survival rate of 65% for patients in Group 2, 71% for patients in Group 1, 79% for patients in Group 3 and 81% for patients in Group 4 (p = 0.02). Actuarial survival of patients with inducible sustained ventricular tachycardia or ventricular fibrillation suppressed by electrophysiologically guided drug therapy was not significantly different from that in patients whose arrhythmia was not suppressed. Multivariate regression analysis revealed that only the presence of congestive heart failure was an independent predictor of outcome in these patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Right versus left ventricular stimulation: influence on induction of ventricular tachyarrhythmias in dogs

The contribution of left (versus right) ventricular stimulation to the induction of ventricular tachyarrhythmias was studied in 37 dogs with chronic experimental myocardial infarction, and 17 dogs with normal hearts. Programmed stimulation of the endocardium at both ventricular apices employed an aggressive protocol of up to 7 extrastimuli. The right ventricle was the most successful site for induction of ventricular tachycardia after myocardial infarction (74% of dogs with ventricular tachycardia). Ten of 11 animals with slow ventricular tachycardia (greater than or equal to 140 msec) were inducible from the right ventricle. In contrast, left ventricular stimulation was required to induce rapid ventricular tachycardia (cycle length less than 140 msec) in 5 of 10 dogs (P less than 0.05). No animal required more than five extrastimuli from any site for induction of ventricular tachycardia. In the normal heart, ventricular fibrillation was induced most often from the right ventricle (77% of dogs) when compared with the left ventricle (47%, P less than 0.05). Ventricular tachycardia was never induced in normal animals. These results show that the right ventricular apex is the most successful site for induction of "slow" ventricular tachycardia in this canine model when using five extrastimuli. Rapid ventricular tachycardia is frequently induced from the infarcted left ventricle, but this arrhythmia may not be clinically significant. The normal right ventricle is significantly more susceptible to ventricular fibrillation than is the left ventricle, but this does not interfere with induction of ventricular tachycardia in the infarcted heart.

Programmed electrical stimulation after myocardial infarction and reperfusion in conscious dogs

The hemodynamic and electrophysiologic variables and the inducibility of arrhythmias were studied before coronary artery occlusion (CAO, 4h) and on days 4, 14, and 28 of the late reperfusion phase in conscious, chronically instrumented dogs. Despite a lack of significant changes in the hemodynamic and the electrophysiologic variables, the response to programmed electrical stimulation (PES) before and after CAO with subsequent reperfusion varied substantially. Before intervention arrhythmias such as sustained ventricular tachycardia (SVT) or ventricular fibrillation (VFib) could not be induced by PES via ultrasonic crystals located subendocardially (LAD and LCX region) or via common stimulation electrodes (right ventricle) in any of six instrumented animals. All six animals were inducible after CAO and reperfusion. Five animals showed SVT and one animal showed VFib in response to stimulation on days 4 and 14 of the late reperfusion phase after CAO. On day 28 four animals showed SVT, and two showed VFib. Antiarrhythmic drug testing carried out in the late reperfusion phase with lidocaine (1 mg/kg bolus followed by continuous infusion) revealed 50% efficacy at a dosage of 40 micrograms/kg/min, 100% at 80 micrograms/kg/min, and 67% at 120 mu/kg/min. The persistent inducibility of arrhythmias for the entire experimental period of 24 days may be attributable to the following features of our model: 1. Electrical stimulation carried out from three different locations. 2. The use of up to three extrastimuli in the PES studies. 3. The use of conscious dogs during CAO, reperfusion, and PES. This novel experimental approach thus promises to be of clinical relevance for the investigation of new antiarrhythmic drugs.

Programmed ventricular stimulation using up to two extrastimuli and repetition of double extrastimulation for induction of ventricular tachycardia: a new highly sensitive and specific protocol

The sensitivity and specificity of a new protocol of programmed ventricular stimulation were evaluated in 71 consecutive patients who were divided into 2 groups: group 1 included 41 patients, of whom 25 had sustained ventricular tachycardia (VT) not associated with cardiac arrest and 16 had ventricular fibrillation (VF) not precipitated by any obvious factor; group 2 included 30 patients without demonstrable heart disease and no suspected or documented sustained ventricular tachyarrhythmias. The study consisted of a standard protocol (up to 2 extrastimuli given only once for each extrastimulus prematurity, 2 right ventricular sites and 3 basic pacing cycle lengths, as well as rapid ventricular pacing) in which double extrastimulation at the shortest coupling intervals that allowed ventricular capture was repeated 10 times. A stimulus current of 3 mA was used. Sustained ventricular tachyarrhythmias were induced in 23 of 25 (92%) patients who presented with sustained VT, 14 of 16 (88%) patients who presented with VF and 2 of 30 (7%) group 2 patients. Eighteen of 25 (72%) patients with sustained VT but only 4 of 16 (25%) with VF had arrhythmias inducible at "immediate" trials of single or double extrastimulation (p less than 0.01). Repetition of double extrastimulation increased the yield of inducible sustained ventricular tachyarrhythmia to 92% in patients with sustained VT (+20%, p = 0.14) and 75% (+50%, p = 0.013) in patients with VF. Rapid right ventricular pacing added a 13% increase in the overall yield in patients with VF. This new protocol of programmed ventricular stimulation has both high sensitivity (90%) and specificity (93%) for induction of sustained VT.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of basic drive cycle length on the yield of ventricular tachycardia during programmed ventricular stimulation

The yield of sustained, monomorphic ventricular tachycardia (VT) induced by programmed ventricular stimulation was compared, using basic drive trains of 400 ms, 600 ms and sinus rhythm, to identify the most efficient sequence of basic drive trains to use during programmed stimulation. Fifty-five patients with coronary artery disease and inducible sustained monomorphic VT not requiring countershock to terminate underwent 81 electrophysiology tests in which 1 to 3 extrastimuli were introduced during sinus rhythm and after basic drive trains of 600 and 400 ms. In 72 electrophysiology tests, sustained, monomorphic VT was induced at the right ventricular apex. The yield of VT using a drive cycle length of 400 ms was 63 of 72 (88%), compared to 46 of 72 (64%) when the drive cycle length was 600 ms, and 23 of 72 (32%) when the extrastimuli were introduced during sinus rhythm (p less than 0.001 for all pairwise comparisons). In 14 electrophysiology tests in which VT was not induced using a 400 ms basic drive cycle length at the apex, the yield of VT was higher using a 400 ms drive cycle length at a second right ventricular site (12 of 14) than with a 600 ms drive cycle length (3 of 12) or sinus rhythm (4 of 12) at the apex (p less than 0.05). The yield of sustained, monomorphic VT induced by 1 to 3 extrastimuli increases as the basic drive cycle length shortens. Whereas programmed stimulation is conventionally started during sinus rhythm or with a drive cycle length of 600 ms, the present results suggest that starting with a drive cycle length of 400 ms may be more efficient.

Natural history of patients with unexplained syncope and a nondiagnostic electrophysiologic study

The purpose of this study was to define the natural history of 99 patients with unexplained syncope who underwent an electrophysiologic test that either was entirely normal or demonstrated nonspecific abnormalities that were nondiagnostic (inducible polymorphic ventricular tachycardia or ventricular fibrillation, a mildly prolonged sinus node recovery time of less than 2 s, a His-ventricular interval of 55 to 99 ms or supraventricular tachycardia not associated with hypotension). The mean age (+/- SD) of the patients was 56 +/- 19 years; structural heart disease was present in 47 patients and absent in 52. Complete follow-up was available in 95 patients. During 20 +/- 11 months of follow-up, 2 patients (2%) died suddenly, 19 patients (20%) had recurrent syncope and 74 patients (78%) had no further episodes of syncope. Among the 19 patients who continued to have syncope after the electrophysiologic testing, the cause of syncope was established clinically in 4 and was found to be high degree atrioventricular (AV) block (2 patients) or sinus node dysfunction (2 patients). No clinical or laboratory findings distinguished patients who had sudden death or syncope during follow-up from patients who did not. In conclusion, in patients with unexplained syncope who undergo an electrophysiologic test that is nondiagnostic 1) the incidence of sudden death is low (2%); 2) the remission rate of syncope is high (80%); 3) the electrophysiologic test may be documented to have been falsely negative in greater than or equal to 20% of patients who continue to have syncope, syncope in these patients being caused by AV block or sinus node dysfunction; and 4) patients at risk of sudden death or recurrent syncope, or both, cannot be readily identified prospectively.

Permanent antitachycardia pacemaker therapy for ventricular tachycardia

This article describes our experience with an antitachycardia pacemaker alone (N = 3) or in combination with an automatic implantable cardioverter defibrillator (AICD, N = 8) in the treatment of ventricular tachycardia. Eleven patients (mean ejection fraction 31%, mean age 67 years) received an antitachycardia pacemaker. Nine had their units programmed for automatic antitachycardia pacing, one unit was programmed to automatic antitachycardia pacing by magnet activation only, and one to tachycardia detection and bradycardia support. Of the nine patients with automatic antitachycardia pacing, seven received appropriate and successful pace termination of spontaneous ventricular tachycardia at up to 120 times per month. Eight of these nine have had AICD implantations as well. There were no operative complications. Over a mean (+/- SD) follow-up of 12.1 +/- 9.3 months (range 3-29 months), there have been two deaths, both due to heart failure. There have been four AICD discharges in three patients. Two units discharged in a clinically appropriate setting. The other two units, both with rate cutoffs less than 200 beats/min, were inadvertently triggered by the antitachycardia pacemaker and/or the underlying rate. In addition to the careful selection of the defibrillator rate cutoff, adverse device-device interactions were avoided by careful intraoperative lead positioning, and the disabling of bradycardia pacing when not needed or contraindicated. Antitachycardia pacing, with the safety provided by the AICD, is an effective treatment for patients with medically refractory ventricular tachycardia.

Antiarrhythmic efficacy of solitary beta-adrenergic blockade for patients with sustained ventricular tachyarrhythmias

To assess the efficacy and predictability of solitary beta-adrenergic blocker (BB) therapy for ventricular tachyarrhythmia (VT), 30 patients (16 men and 14 women) with a mean age of 55 years, who initially had sustained ventricular tachycardia (70%) or ventricular fibrillation (30%), were studied. Results of baseline arrhythmia tests showed VT on ECG monitoring in 57% of the patients, during exercise in 50%, induced by programmed stimulation in 69%, increasing to 86% during isoproterenol. BB therapy prevented inducible VT during programmed stimulation in 37% of the patients, prevented VT on ECG monitoring in 54%, and prevented VT during exercise in 83%. Long-term BB therapy was given to 24 of 30 patients, whereas six other patients with hemodynamically unstable VT during BB therapy received other long-term treatment. During a mean follow-up of 824 days, 6 of 24 patients had recurrent VT. BB therapy was discontinued in two patients because of side effects. Long-term success was predicted by left ventricular ejection fraction greater than 45%, absence of coronary disease, and age less than 60 years (all p less than 0.02). Neither suppression of arrhythmia during exercise testing, nor results of programmed stimulation or ECG monitoring were predictive of outcome. Thus beta-adrenergic blockers can be effective as solitary antiarrhythmic therapy in selected patients with VT.

Sudden cardiac death: etiologies, pathogenesis, and management

Sudden death claims an estimated 350,000 lives per year in the United States. When death occurs within 1 hour of the onset of symptoms, 90% are the result of ventricular tachyarrhythmias. The majority of victims are middle-aged men with coronary artery disease, but in approximately 25%, sudden death is the presenting manifestation of their problem. In some populations, the detection of premature ventricular complexes (PVCs) by ambulatory monitoring is predictive of an increased risk of sudden death. However, the arrhythmia that best predicts this risk is unclear, and ambient arrhythmias are only a modest marker of this risk. Therapy to suppress asymptomatic PVCs has not been shown to be effective in preventing sudden death, and in some cases, lethal arrhythmias can be prevented without significant effects on ambient arrhythmias. Other risk markers such as depressed left ventricular function and the presence of low-amplitude, long-duration, late potentials recorded on a signal averaged electrocardiogram are more powerful predictors of risk than are PVCs. These latter findings in particular support the presence of areas of slow electrical conduction (a requirement for reentrant mechanism arrhythmias) and suggest that an abnormal electrical environment or "substrate" is the most important factor in this problem. The management of patients at risk for sudden death is controversial. While postinfarct survivors with arrhythmias constitute a population at increased risk, the absolute risk is only about 5% in the first year and has not been shown to be improved by conventional antiarrhythmic drugs. Small study size, arrhythmia variability, ill-defined end points, and proarrhythmia may partially explain this apparent lack of efficacy. The prophylactic use of antiarrhythmic drugs other than beta-blockers to prevent sudden death in asymptomatic populations at risk is therefore of unproven benefit. By contrast, patients who have survived a life-threatening arrhythmia unrelated to an acute myocardial infarction have an approximately 30% risk of recurrence in the following year. In these patients, the use of ambulatory monitoring to guide therapy is limited by the high incidence of false-negative responses (lethal arrhythmia recurrence despite ambient arrhythmia suppression) and the lack of frequent spontaneous arrhythmias in many patients. In this patient population, electrophysiological testing can be used to prognosticate recurrence and gain insight into arrhythmia mechanism, stability, and hemodynamic tolerance. The technique is also useful in guiding both pharmacological and nonpharmacological therapy.(ABSTRACT TRUNCATED AT 400 WORDS)

Rapid self-terminating ventricular tachycardia induced during electrophysiologic study: a prospective evaluation

The clinical significance of rapid self-terminating ventricular tachycardia induced during electrophysiologic study was prospectively evaluated in three patient groups with clinical ventricular arrhythmias. Group A (11 patients) had inducible rapid self-terminating ventricular tachycardia only (mean cycle length less than or equal to 250 ms and greater than or equal to 10 beats in duration). In Group B (22 patients) induction of this arrhythmia was followed by the induction of sustained ventricular tachycardia. In Group C (82 patients) sustained ventricular tachycardia was induced without preceding rapid self-terminating ventricular tachycardia. All clinical characteristics of Group B patients were similar to those of Group C patients but differed markedly from those of Group A patients. Compared with Group A patients, Group B patients had a lower left ventricular ejection fraction (32 +/- 13% versus 52 +/- 17%, p = 0.004) and a greater prevalence of coronary artery disease (82% versus 0%, p less than 0.0001), structural heart disease and a history of clinical sustained ventrical arrhythmias. Similarly, the induced self-terminating ventricular tachycardia differed in Group A and Group B patients. The arrhythmias in Group B patients were more often monomorphic, were more often induced with one or two extrastimuli and had a longer cycle length than those in Group A patients. In Group B patients, the electrophysiologic characteristics of the self-terminating and the sustained induced ventricular tachycardias were similar. Cardioversion was required in 50% of Group B patients compared with 27% of Group C patients (p = 0.038).(ABSTRACT TRUNCATED AT 250 WORDS)