Electrophysiologic investigation in Brugada syndrome; yield of programmed ventricular stimulation at two ventricular sites with up to three premature beats.

INTRODUCTION: Numerous reports on the inducibility of ventricular tachyarrhythmias (VT) in patients with atypical right bundle branch block and right precordial ST-elevation (Brugada syndrome) are based on multicentre studies that have used different stimulation protocols. Therefore, we prospectively investigated the inducibility of VT in these patients using a uniform protocol. METHODS: In 41 consecutive patients (29 males) showing a pattern of right bundle branch block and ST-elevation, programmed ventricular stimulation was performed in the right ventricular apex with up to three premature stimuli at sinus rhythm and at four different paced cycle lengths (500, 430, 370, and 330 ms) until refractoriness was reached or reproducible induction of a sustained (>30s) VT occurred. If a VT was not reproducibly inducible, the same protocol was repeated in the right ventricular outflow tract. RESULTS: A history of life-threatening events defined as syncope (n=17) or aborted sudden cardiac death (n=13) was present in 30 patients (73%); 11 individuals were asymptomatic. Inducibility (68%) was similar between symptomatic (n=21, 70%) and asymptomatic patients (n=7, 64%). In 16 (39%) patients, VT were reproducibly inducible. If patients were only stimulated in the right ventricular apex, inducibility rate decreased to 39%. If only two premature beats at two sites were used it was as low as 32%. The mean coupling intervals of the second and third premature stimuli inducing sustained VT were short: 189+/-21 ms vs 186+/-22 ms, respectively. Forty-four percent of all patients (i.e. 64% of the inducible patients) had inducible VT only with coupling intervals shorter than 200 ms. CONCLUSIONS: The stimulation protocol markedly influences the extent of inducibility of VT in patients with right bundle branch block and ST-segment elevation. These findings question the significance of previous multicentre studies using different stimulation protocols and should have implications for further studies.     

Programmed electrical stimulation in healed myocardial infarction using a standardized ventricular stimulation protocol

The diagnostic accuracy of programmed electrical stimulation was prospectively assessed in 111 patients with myocardial infarction (MI) with or without a history of spontaneous ventricular arrhythmias. In 29 patients neither ventricular tachycardia (VT) nor episodes of 10 premature ventricular depolarizations per hour was documented. Fifty patients had documented nonsustained VT and 32 had sustained monomorphic VT. One and 2 extrastimuli (twice diastolic threshold, 2 ms in duration) were given during sinus rhythm and ventricular pacing at 100, 120 and 140 beats/min in the right ventricular apex (part I). When this protocol failed to induce a sustained monomorphic VT, a third extrastimulus was introduced (part II). Repetitive ventricular responses were induced in all patients, and in 15 (14%) polymorphic ventricular arrhythmias requiring DC shock were induced. Incidence of initiation of sustained monomorphic VT and polymorphic ventricular arrhythmias requiring DC shock was related to the clinical arrhythmia and the stimulation protocol. In patients with documented sustained monomorphic VT, a third extrastimulus only increased the incidence of sustained monomorphic VT (68% to 94%), whereas in patients with documented nonsustained VT and without VT the incidence of both polymorphic and monomorphic arrhythmias increased by 7 to 12%. Sustained monomorphic VTs induced in patients without such a history were faster (p less than 0.01), depended on site of MI (p less than 0.05) and were more often preceded by nonsustained polymorphic VT (p less than 0.01) than in patients with documented sustained monomorphic VT.(ABSTRACT TRUNCATED AT 250 WORDS)     

Usefulness of QRS prolongation in predicting risk of inducible monomorphic ventricular tachycardia in patients referred for electrophysiologic studies

QRS prolongation on surface electrocardiography has been identified as a marker for increased cardiac mortality. A potential mechanism for increased mortality is ventricular tachycardia (VT). This study aimed to evaluate the relation between bundle branch block and sustained monomorphic VT inducibility in patients referred for electrophysiologic studies. We analyzed a cohort of 777 patients (age 63 +/- 18 years, 67% men, left ventricular [LV] ejection fraction [EF] 45% +/- 16, prior myocardial infarction 41%) referred for electrophysiologic studies between 1994 and 2001 who underwent programmed stimulation for VT. Forty-five percent of patients were referred for syncope or a history of VT and/or ventricular fibrillation. Thirty-one percent of patients had prolonged QRS duration (> or =120 ms). Patients with prolonged QRS duration were older, had lower LVEFs, and were more likely to have a history of myocardial infarction. Prolonged QRS was a significant predictor of sustained monomorphic VT inducibility (p <0.0001). On multivariate analysis correcting for age, sex, LVEF, history of myocardial infarction, medications, and QRS conduction delay proved to be independently associated with sustained monomorphic VT inducibility (relative risk 3.290, 95% confidence interval 2.185 to 4.953 for prolonged vs normal QRS duration). Thus, a prolonged QRS duration on surface electrocardiography is a strong, independent predictor of inducible sustained monomorphic VT. Conduction delay may be an important risk factor, providing a substrate for the development of reentrant monomorphic VT, and furthermore suggests a potential mechanism for the increased mortality observed in patients with prolonged QRS.     

Comparison of the results of programmed ventricular stimulation from the right ventricular apex and outflow tract: a randomized, prospective study

Objective: The aim of this prospective study was to analysethe yield of programmed ventricular stimulation at the rightventricular apex compared with the outflow tract. Methods: A stepwise randomized cross-over protocol of programmedventricular stimulation with alternating stimulation at bothsites was used in 66 patients who were studied because of sustainedventricular tachycardia (n = 30), ventricular fibrillation (n= 7), or non-sustained ventricular tachycardia and/or syncope(n = 29). Results: There were no significant differences between the resultsof stimulation from either right ventricular site with regardto the presence or absence of structural heart disease, spontaneousarrhythmia, ejection fraction or effective refractory periods.Overall, monomorphic ventricular tachycardia was inducible in33 patients (50%); in 25 patients (75.8%), this arrhythmia wasinduced from both sites. However, in only 17 of these 25 patients(68%) did the induced monomorphic ventricular tachycardias havethe same morphologies and similar (± 50 ms) cycle lengths.Ventricular fibrillation was inducible in 11 patients (17%),mostly by three extrastimuli (n=8; 73%). Conclusions: (1) stimulation from at least two right ventricularsites is desirable because of their independent contributionto the induction of ventricular tachyarrythmias, (2) the non-inducibilityor inducibility at one ventricular site does not predict theeffect at another stimulation site, (3) the effective refractoryperiod at the right ventricular apex and outflow tract do notdiffer, (4) the inducibility of multiple ventricular tachycardiamorphologies emphasizes the importance of documenting the causeof spontaneous arrhythmias with multiple electrocardiographicleads to ensure the correct interpretation of arrhythmias inducedby programmed stimulation, (5) clinical or haemodynamic featurescannot predict whether one or more stimulation sites will berequired for induction of ventricular tachycardia. These resultsare important for the diagnostic evaluation and assessment ofpharmacological or non-pharmacological interventions.     

Prognostic significance of repetitive ventricular response in chronic coronary artery disease

A prospective study was conducted in 267 patients with angiographically defined coronary artery disease without documented ventricular tachycardia to determine the prognostic significance of repetitive ventricular response (RVR) after programmed electrical stimulation (PES). The patients were classified inducible if RVR with 3 or more echo beats (RVR greater than or equal to 3) could be induced. 89 patients without previous myocardial infarction (MI), 61 survivors of MI occurring between 6 weeks and 3 months before and 117 patients who had survived longer than 3 months after MI were studied. A standardized stimulation protocol with single (S1S2) and double (S1S2S3) extrastimuli during ventricular drive at a cycle length of 600, 500 and 430 ms with a current strength below 5 mA at the right ventricular apex was employed. Ventricular responses with 3 to 5 echo beats (RVR3-5) and with 6 and more echo beats (RVR greater than or equal to 6) were distinguished. In 68 (25%) patients RVR3-5 and in 38 (14%) patients RVR greater than or equal to 6 was observed; in 11 patients with RVR greater than or equal to 6 sustained VT was initiated which was monomorphic in 5 of them. The occurrence of RVR greater than or equal to 6 was related to the time interval to prior MI and most frequently found within 3 months of MI. A higher incidence of RVR greater than or equal to 6 was observed in more advanced CAD, although the angiographic findings were unable to predict the results of PES. During a mean follow up of 20 months 11 patients died, 8 suddenly, 3 in cardiac failure. Those who died had more extensive CAD, RVR greater than or equal to 3 was found in 4 of them and nonsustained VT in one. The sensitivity of RVR greater than or equal to 3 as a predictor of sudden death (SD) was 36% and the specifity 60%. The predictive value of inducibility of RVR greater than or equal to 3 as indicator of SD was 4% and the predictive value of noninducibility was 98%. It is concluded that in patients with chronic CAD without spontaneous VT, RVR with 3 more echo beats does not identify a predisposition to die suddenly.     

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.     

Prospective comparison of right and left ventricular stimulation for induction of sustained ventricular tachycardia

Thirty-eight patients who had sustained monomorphic ventricular tachycardia (VT) or sudden cardiac death underwent programmed ventricular stimulation. To assess the relative efficacy of right and left ventricular (RV and LV) stimulation, a tandem protocol with 1 to 4 extrastimuli and burst pacing was used. Each step of the protocol was performed in a rotating sequence at the RV apex, basal RV septum and LV apex. Sustained VT was induced from the RV apex in 26 patients, right ventricle (either site) in 27, and LV apex in 24, and spontaneous VT was reproduced from those sites in 11, 14 and 12 patients, respectively. In the 23 patients who had sustained VT induced from both ventricles, RV stimulation always required fewer or the same number of extrastimuli for induction. At every stage of the protocol, the cumulative yield of sustained VT was consistently greater from the right ventricle than from the left ventricle. After delivering 4 extrastimuli and burst pacing, LV stimulation only increased the yield of sustained VT by 1 patient, and spontaneous VT by 3 patients. Inducibility or noninducibility in the right ventricle generally predicted the same outcome in the left ventricle. Previously undocumented VT or ventricular fibrillation was induced from the right ventricle in 19 patients and from the left ventricle in 13. Thus, LV stimulation was less efficacious than RV stimulation. LV stimulation increased the yield over RV stimulation only minimally and did not reduce the number of extrastimuli required to induce sustained VT.     

Prospective comparison of a conventional and an accelerated protocol for programmed ventricular stimulation in patients with coronary artery disease

BACKGROUND. This study compared the sensitivity, specificity, and efficiency of a "conventional" and "accelerated" programmed stimulation protocol in 293 patients with coronary artery disease who had a history of sustained or nonsustained monomorphic ventricular tachycardia (VT). METHODS AND RESULTS. In the conventional protocol, one and two extrastimuli were introduced during sinus rhythm and during basic drive trains at cycle lengths of 600 and 400 msec at the right ventricular apex and then at the outflow tract or septum. In the accelerated protocol, one, two, and then three extrastimuli were introduced at each of three basic drive train cycle lengths (350, 400, and 600 msec) at the right ventricular apex; the procedure was repeated at a second right ventricular site. Six hundred thirty-four electrophysiological tests were performed using one of these two protocols either in the baseline state (293 tests) or during drug testing (341 tests). The yield of sustained, monomorphic VT was 89% with the conventional protocol and 92% with the accelerated protocol during baseline tests in patients who had a history of sustained VT (p = 0.05); 20% and 34%, respectively, during baseline tests in patients with a history of nonsustained VT (p = 0.06); and 70% and 77%, respectively, during drug testing (p = 0.2). To induce sustained, monomorphic VT, 10.1 +/- 5.0 (mean +/- SD) protocol steps and 14.4 +/- 8.7 minutes were required with the conventional protocol, compared with 4.0 +/- 3.7 steps and 5.6 +/- 6.1 minutes with the accelerated protocol (p less than 0.001 for each comparison). Among the tests in which sustained, monomorphic VT was induced, sustained polymorphic VT or ventricular fibrillation was induced more often with the conventional protocol (3.6%) than with the accelerated protocol (0.9%, p = 0.05). CONCLUSIONS. The efficiency of programmed stimulation can be improved by the early use of a basic drive train cycle length of 350 msec and three extrastimuli. Compared with a conventional stimulation protocol, the accelerated protocol used in this study reduces the number of protocol steps and duration of time required to induce monomorphic VT by an average of more than 50% and improves the specificity of programmed stimulation without impairing the yield of monomorphic VT.     

Comparative evaluation of the results of Holter monitoring and programmed ventricular stimulation in patients with ischemic heart disease

24-hour ECG Holter monitoring and programmed ventricular stimulation were performed in 81 patients (64 males and 17 females aged 35-65). No ++anti-arrhythythmic agents nor beta-blockers were administrated. 58 patients suffered from myocardial infarction in the past, and 38 had a history of ventricular tachycardia. Right atrial and ventricular stimulation (in 7 patients also left ventricular stimulation) was performed using stimuli of a 2 ms pulse width. 24-hour ECG Holter monitoring was recorded on a magnetic tape from two bipolar precordial leads. Both examinations results were compared to assess correlation between ECG Holter monitoring parameters and inducibility of VT or VF by programmed stimulation. Significant correlation was stated among occurrence of: 1) spontaneous sustained ventricular tachycardia and induced by stimulation monomorphic sustained VT (p less than 0.005) as well as estimated both sustained and nonsustained VT (p less than 0.010) 2) spontaneous nonsustained VT and induced by stimulation sustained or nonsustained monomorphic VT (p less than 0.025). There was no correlation between spontaneous ventricular arrhythmias estimated by Lown and Wolf's classification and possibility to induce monomorphic VT as well as between any of ECG Holter monitoring parameters and polymorphic VT or ventricular fibrillation induced by stimulation. Aggressiveness extent of stimulation protocol necessary to induce monomorphic VT was similar in patients with or without VT recorded by Holter method.     

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)     

Usefulness of early versus late programmed ventricular stimulation in acute myocardial infarction

To determine the influence of timing on the prognostic value of programmed ventricular stimulation after acute myocardial infarction (AMI), 32 patients were studied on day 19 (early study) and again on day 36 (late study) after AMI using up to 3 extrastimuli. At the early study, sustained monomorphic ventricular tachycardia (VT) was induced in 12 patients (38%), sustained polymorphic VT in 8 (25%), nonsustained monomorphic VT in 1 (3%), nonsustained polymorphic VT in 1 (3%) and no inducible arrhythmia in 10 (31%). At the late study, sustained monomorphic VT, nonsustained monomorphic VT and nonsustained polymorphic VT were induced in 8 patients (25%) each, and no inducible arrhythmia in 8 (25%). Of the 12 patients who had inducible sustained monomorphic VT at the early study, 7 had noninducibility of sustained monomorphic VT at the late study. Of the 20 patients who had noninducibility of sustained monomorphic VT at the early study, 3 had inducible sustained monomorphic VT at the late study. During the follow-up period (mean +/- standard deviation 21 +/- 8 months), there were 2 sudden cardiac deaths and 3 occurrences of sustained VT. Univariate analysis revealed both inducibilities of sustained monomorphic VT at the early study (p = 0.045) and at the late study (p less than 0.001) to be predictive of sudden cardiac death or clinical occurrence of sustained VT. However, inducibility of sustained monomorphic VT at the late study had a higher sensitivity (100%), specificity (89%), positive predictive value (63%) and negative predictive value (100%) than at the early study (80, 70, 33 and 95%, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

Prognostic significance of sustained monomorphic ventricular tachycardia induced by programmed ventricular stimulation using up to triple extrastimuli in survivors of acute myocardial infarction

The prognostic significance of sustained monomorphic ventricular tachycardia (VT) induced by programmed ventricular stimulation using up to 3 extrastimuli was evaluated in 133 consecutive survivors of acute myocardial infarction (AMI) at a mean interval of 1.8 +/- 1.1 months after onset. This was compared with hemodynamic and angiographic abnormalities shown by cardiac catheterization and ventricular ectopic activity detected by Holter monitoring. Sustained monomorphic VT was induced in 25 (19%) patients, sustained polymorphic VT in 11 (8%) patients, nonsustained monomorphic VT (greater than or equal to 10 beats) in 12 patients (9%) and nonsustained polymorphic VT in 9 patients (7%). Multivariate logistic regression analysis of clinical, angiographic, hemodynamic and electrocardiographic variables showed that the presence of a left ventricular aneurysm (p = 0.005) and Lown grade 4B ventricular ectopic activity (p less than 0.001) were independent predictors of inducibility of sustained monomorphic VT. During a mean follow-up of 21 +/- 13 months, there were 8 (6%) sudden cardiac deaths and 3 (2.3%) spontaneous occurrences of life-threatening sustained VT. The 2-year probability of freedom from sudden cardiac death or sustained ventricular tachyarrhythmias was 53 +/- 13% for patients with inducible sustained monomorphic VT, 70 +/- 10% for those with a left ventricular ejection fraction less than 40% and 58 +/- 13% for those with Lown grade 4B ventricular ectopic activity.(ABSTRACT TRUNCATED AT 250 WORDS)     

A new protocol of programmed stimulation for assessment of predisposition to spontaneous ventricular arrhythmias

We have devised a simple method for identifying predispositionto spontaneous sustained ventricular fibrillation (VF) and tachycardia(VT). A standardized protocol of programmed stimulation wasapplied to 111 control subjects without ventricular diseaseand with no history of VF or VT (Group I) and to 27 patientswith previous myocardial infarction and documented spontaneous(in the absence of evidence of further acute myocardial ischaemia)VF or VT (Group II). The stimulation protocol consisted of singleand paired ventricular extrastimuli introduced during ventriculardrive at the right ventricular apex and ouflow tract, at twicediastolic threshold current intensity and at 20 mA. None ofthe Group I subjects exhibited VF or sustained (more than 10s) VT. In contrast sustained arrhythmias were induced in 24(89%) of Group II patients. We conclude: In our study population,initiation of a sustained ventricular tachyarrhythmia at programmedstimulation was both a sensitive (89%) and specific (100%) indicatorfor predisposition to spontaneous VF and VT.     

Electrophysiologic effects of bepridil in patients with refractory ventricular tachycardia assessed by programmed electrical stimulation

The effect of intravenous bepridil, a new calcium antagonist with class I and III properties, was tested in 21 patients with sustained ventricular tachyarrhythmias refractory to a mean of five antiarrhythmic agents as assessed by programmed right ventricular stimulation. At control electrophysiologic study without antiarrhythmic agents, sustained monomorphic ventricular tachycardia (VT) was initiated in 20 patients and ventricular fibrillation (VF) was initiated in one patient. After 3 mg/kg of bepridil was administered, VT was still inducible in 19 patients (3 patients had self-terminating VT); the other 2 patients had no inducible VT after bepridil. Bepridil prolonged significantly the QTc interval, the effective refractory period, and the cycle length of induced ventricular tachycardia. Two patients with no inducible VT after intravenous bepridil were placed on oral bepridil (300 mg/day). One patient died suddenly and one patient died of progressive heart failure. The results seem to indicate that the efficacy of bepridil in patients with refractory ventricular tachycardia is limited.     

Comparative effects of anti-arrhythmia agents on ventricular refractory period and prevention of ventricular tachycardia induced by stimulation]

The efficacy of antiarrhythmic drugs is attributed to their actions on the refractory periods or conduction velocity in the reentry circuit. The aim of this study was to determine the relationship between these factors and the prevention of electrically inducible ventricular tachycardia (VT). Twenty-seven patients with sustained monomorphic postinfarction VT underwent programmed stimulation under basal conditions and after administration of oral Class I antiarrhythmic drugs. The protocol of stimulation consisted of delivering one to three extrastimuli to the right ventricular apex on two basic cycle lengths. Sustained VT was induced in all patients. After the same protocol under antiarrhythmic therapy (1 to 5 tests, average 2.9 +/- 1) sustained VT could not be induced in 12 patients (44%). The effective right ventricular refractory period was significantly increased in patients without inducible VT under treatment (247 +/- 18 versus 302 +/- 26 ms). The increase in the right ventricular effective refractory period in patients with persistence of inducible VT was much less (from 270 +/- 28 to 287 +/- 30 ms). In all patients in whom several antiarrhythmic drugs were tested the right ventricular effective refractory period was higher when the treatment was judged to be effective (299 +/- 27 ms) than ineffective (272 +/- 27, p < 0.02). The prevention of inducible VT by class I antiarrhythmic agents seems therefore to be related to their effect on the ventricular refractory period.     

Novel mechanism of postinfarction ventricular tachycardia originating in surviving left posterior Purkinje fibers

BACKGROUND: Other than bundle branch reentry and interfascicular reentry, monomorphic postmyocardial infarction (post-MI) reentrant ventricular tachycardia (VT) including the His-Purkinje system has not been reported. Verapamil-sensitive idiopathic left VT includes the left posterior Purkinje fibers but develops in patients without structural heart disease. OBJECTIVES: The purpose of this study was to describe a novel mechanism of reentrant VT arising from the left posterior Purkinje fibers in patients with a prior MI. METHODS: The study consisted of four patients with a prior MI and symptomatic heart failure who underwent electrophysiologic study and catheter ablation for VT showing right bundle branch block (n = 3) or atypical left bundle branch block (n = 1) morphology with superior axis. In two patients, the VT frequently emerged during the acute phase of MI and required emergency catheter ablation. RESULTS: Clinical VT was reproducibly induced by programmed stimulation. In three patients, both diastolic and presystolic Purkinje potentials were sequentially recorded along the left ventricular posterior septum during the VT, whereas in the fourth patient, only presystolic Purkinje potentials were observed. During entrainment pacing from the right atrium, diastolic Purkinje potentials were captured orthodromically and demonstrated decremental conduction properties, whereas presystolic Purkinje potentials were captured antidromically and appeared between the His and QRS complex. Radiofrequency energy delivered at the site exhibiting a Purkinje-QRS interval of 58 +/- 26 ms successfully eliminated the VTs without provoking any conduction disturbances. CONCLUSION: Reentrant monomorphic VT originating from the left posterior Purkinje fibers, which is analogous to idiopathic left VT, can develop in the acute or chronic phase of MI. Catheter ablation is highly effective in eliminating this VT without affecting left ventricular conduction.     

Sequelae of nonsustained polymorphic ventricular tachycardia induced during programmed ventricular stimulation

The results of 206 programmed ventricular stimulation studies performed in 130 patients (100 men and 30 women, mean age 62 +/- 12 years, +/- standard deviation) were examined prospectively to determine the sequelae of nonsustained polymorphic ventricular tachycardia (VT) induced during programmed ventricular stimulation. The clinical indication for the electrophysiologic study was either documented monomorphic VT or unexplained syncope. The pacing protocol included 2 right ventricular pacing sites, 2 basic drive cycle lengths and up to 3 extrastimuli. In 111 studies, nonsustained polymorphic VT was induced and with continuation of the programmed stimulation protocol, sustained monomorphic VT was induced in 48 studies (43%) and polymorphic VT was induced in 13 studies (12%). Overall, sustained monomorphic VT was induced in 110 studies and sustained polymorphic VT in 18 studies. The incidence of nonsustained polymorphic VT preceding the induction of sustained polymorphic VT was significantly greater than the incidence of nonsustained polymorphic VT preceding the induction of sustained monomorphic VT (72 vs 44%, p less than 0.05). Nonsustained polymorphic VT is not a useful predictor of the outcome of programmed ventricular stimulation. The use of nonsustained polymorphic VT as an endpoint for stimulation would be likely to improve the specificity of programmed ventricular stimulation by limiting the induction of sustained nonclinical arrhythmias that require countershock, but at the cost of significantly impairing the yield of monomorphic VT.     

The Value of Electrophysiologic Testing in Patients Resuscitated From Documented Ventricular Fibrillation

EP Study and Ventricular Fibrillation. Introduction: Electrophysiologic testing is performed in patients resuscitated from ventricular fibrillation (VF) on the assumption that sustained monomorphic ventricular tachycardia (VT) may be a precursor to VF, with the former amenable to assessment by serial drug testing.
Methods and Results: We assessed the usefulness of this strategy by analyzing clinical and electrophysiologic data of 42 survivors (29 men and 13 women; mean age 54 ± 14 years) of VF without a reversible cause. All patients had VF documented on ECG and required defibrillation. Underlying heart diseases included coronary disease in 28, dilated cardiomyopathy in 3, arrhythmogenic right ventricular dysplasia in 1, and no apparent structural heart disease in 10 patients. Only 2 (4.7%) patients had a prior history of documented VT. The electrophysiologic study was performed 7 to 30 days after VF. Programmed stimulation at the right ventricular apex using at least two drive cycle lengths and up to three extrastimuli induced sustained monomorphic VT in 4 (9.5%), sustained polymorphic VT in 3 (7.1%), nonsustained monomorphic VT in 1 (2.3%), nonsustained polymorphic VT in 5 (11.9%), and VF in 13 (30.9%) patients. Two patients with documented prior VT and coronary disease had sustained VT induced during the electrophysiologic study. On the other hand, sustained monomorphic VT was induced in 53 of the 59 (90%) patients (45 men and 14 women; mean age 57 ± 16 years) with clinically documented VT concurrently studied using the same stimulation protocol.
Conclusion: We conclude that reproducible induction of sustained monomorphic VT in survivors of documented VF is uncommon. It may be more cost effective to proceed directly to treatment with implantable cardioverter defibrillators in these patients.     

Programmed ventricular stimulation after myocardial infarction does not help reduce the risk of ventricular events

Summary Programmed ventricular stimulation could be a useful technique to detect patients at high risk for ventricular arrhythmias and sudden death after acute myocardial infarction. However, prevention of arrhythmic events using this technique has never been demonstrated. To determine whether prophylactic antiarrhythmic therapy influences prognosis after acute myocardial infarction, 196 patients without spontaneous ventricular tachycardia (VT) but with inducible sustained monomorphic VT were followed for 3±1 years. Ninety-seven patients were not treated (control group). In 99 patients (study group), the antiarrhythmic therapy was guided by electrophysiologic study: One to four trials using class I, II, and III antiarrhythmic drugs were performed until the VT was not inducible or the induced VT was slower and was associated with hemodynamic stability. An effective antiarrhythmic drug prevented VT induction in 34 patients (34%; group I). Sixty-five patients (group II) still had inducible VT with the antiarrhythmic drug. Group II differed from group I in having a higher incidence of an inferior myocardial infarction location (57% vs. 47%; NS), a lower left ventricular ejection fraction (36.5% vs. 41%; NS), a slower rate of induced VT in the control state (227 vs. 255 beats/min; p<0.05), and a higher number of drug trials (1.9 vs. 1.3; p<0.001). During the follow-up in the control group and in groups I and II, the incidence of total cardiac events was 25%, 15%, and 16% (NS), respectively, and the incidence of total arrhythmic events (VT, sudden death) was 18.5%, 9%, and 12% (NS). Only the risk of VT was reduced (14%, 0%, and 4%; p<0.05). In conclusion, guided-antiarrhythmic therapy, including class III agents after acute myocardial infarction, was successful in only 34% of patients, and the incidence of arrhythmic events was not significantly decreased. Therefore, programmed ventricular stimulation does not help in managing patients at risk of ventricular arrhythmia after myocardial infarction but could help to indicate the need for nonmedical treatment, such as device therapy.     

Limited value of programmed electrical stimulation from multiple right ventricular pacing sites in clinically sustained ventricular fibrillation or ventricular tachycardia associated with coronary artery disease

One-hundred and fifty patients with coronary artery disease and a documented history of sustained ventricular tachyarrhythmias were studied to determine if programmed electrical stimulation (PES) from a second right ventricular (RV) pacing site optimizes the induction of such sustained arrhythmias. The first PES test was performed from 2 RV pacing sites (apex and outflow tract or septum) using the apex first in each patient. All patients underwent a second PES within 6 to 24 hours of the first; both studies used up to 4 ventricular extrastimuli, in the absence of antiarrhythmic treatment. The second PES was performed from a single RV apical site using a pacing catheter retained from the first study. During the first day's study, 74 patients (49%) had sustained ventricular tachycardia induced from the RV apex. Only 11 of the remaining 76 patients (7% of the total group) were inducible exclusively from a second RV pacing location during the first day's testing. Seven of these 11 patients, as well as 15 additional patients who did not have ventricular tachycardia induced from either site on the first day's study, were inducible from the RV apex during the second drug-free study. Among patients with sustained ventricular tachyarrhythmias, limiting PES to a single RV site, with the option of performing a second study in those who are initially noninducible is more effective in inducing sustained ventricular tachyarrhythmias than is PES performed from 2 RV pacing sites.