Episodes Of Monomorphic Ventricular Tachycardia Research Articles

Initiation of monomorphic ventricular tachycardia: electrophysiological, clinical features, and drug therapy in patients with implantable defibrillators

At least 2 distinct patterns of sustained monomorphic ventricular tachycardia (MVT) have been ascribed during analysis of stored intracardiac electrograms retrieved from implantable cardioverter defibrillators and Holter recordings in patients with ventricular arrhythmia. We aimed to investigate the electrophysiological features of MVT with different initiation patterns in patients with implantable cardioverter defibrillators and to assess whether there is a relationship of the initiation patterns of sustained MVT with clinical characteristics and efficacy of antiarrhythmic therapy. Seventy-four stored intracardiac electrograms in 21 patients (mean age of 68.2 ± 4.2 years) with MVT were evaluated. Cardiovascular diagnosis included coronary artery disease in 85.7% of the patients. All MVT episodes were classified as those initiating with ventricular premature beats (nonsudden onset MVT) and those without ventricular ectopy preceding tachycardia (sudden onset MVT). There was significant difference in left ventricular ejection fraction between MVTs with different initiation pattern, being the lower in those with nonsudden onset (33.6% ± 38.4% vs. 38.4 ± 7.0%, P < .04). Ventricular tachycardia cycle length was shorter in group of MVT with nonsudden onset as compared with sudden onset (338.5% ± 48.1% vs. 376.8% ± 57.0%, P < .02). Tachycardia with sudden onset was associated with shorter preceding RR interval than tachycardia with nonsudden onset (821.8 ± 136.2% vs. 748.7 ± 107.7%, P < .01). There were no significant differences in the type of antiarrhythmic drug therapy used between groups ( P > .05). Monomorphic ventricular tachycardias with nonsudden onset occurred more frequently than with sudden onset, without precipitating RR cycles shortening, are faster in rate, associating with lower ejection fraction. Monomorphic ventricular tachycardias with sudden onset are characterized by preceding shortening of RR intervals, slower cycle length, and less worsening of ejection fraction.

Clinical importance of the initiation pattern of monomorphic ventricular tachycardia

We investigated the clinical and electrophysiological features of monomorphic ventricular tachycardia (MVT) with different initiation patterns in patients with implantable cardioverter defibrillator to assess whether there is a relationship between the initiation patterns of sustained MVT and clinical characteristics, and the efficacy of antiarrhythmic and electrical therapy. Fifty-five stored IECGs in twenty-two patients with MVT were evaluated. All MVT episodes were classified as initiating with ventricular premature beats (non-sudden onset MVT) or without ventricular ectopy preceding tachycardia (sudden onset MVT). Non-sudden onset MVT was characterized by shorter tachycardia cycle length (CL) and required higher shock energy for termination. Sudden onset MVT was precipitated by shortening of the sinus CL before tachycardia and was more common with relatively better preserved systolic function.

The Relation of QT Dispersion to Spontaneous Ventricular Arrhythmias During the Acute Phase of Myocardial Infarction

Background: QT dispersion is associated with ventricular arrhythmias and sudden death among patients with a previous myocardial infarction (Ml). The relationship between QT dispersion and ventricular arrhythmias during the acute phase of Ml is uncertain.Methods: Patients enrolled in the Multicenter Study of Silent Myocardial Ischemia who had first Q wave myocardial infarctions (n = 363) were screened for the presence of ventricular arrhythmias during the initial hospitalization. Twelve patients had ventricular fibrillation, and 18 patients had an episode of monomorphic ventricular tachycardia. Each patient who had ventricular arrhythmias was matched with four controls on the basis of age, peak creatine kinase, thrombolysis, and the presence of congestive heart failure. The final study population consisted of 150 patients: 12 patients with ventricular fibrillation (VF+) who were compared to 48 controls (VF—), and 18 patients with ventricular tachycardia (VT+) who were compared to 72 controls (VT–). The RR, QRS, and QT intervals were measured manually using standard 12‐lead ECGs (25 mm/s) obtained after hospital admission. The maximal QT dispersion (maximum — minimum value) was calculated. Multivariate logistic regression analysis was performed to determine if QT dispersion was independently associated with ventricular arrhythmias during the acute phase of Ml.Results: QT dispersion was significantly greater in VF+ patients compared to VF— patients (89 ± 18 ms vs 66 ± 22 ms, P &gt; 0.01). QT dispersion was similar in VT+ and VT— patients (68 ± 25 ms vs 68 ± 26 ms, P = NS). QT dispersion was the only variable that was independently associated with ventricular fibrillation (OR 1.7 for each 10‐ms increment in QT dispersion; 95% Cl 1.2–2.6; P = 0.008). QT dispersion was not associated with monomorphic ventricular tachycardia (OR 1.0; 95% Cl 0.8–1.2; P = NS).Conclusion: QT dispersion is independently associated with ventricular fibrillation, but not monomorphic ventricular tachycardia, during the acute phase of Ml.

The mode of onset of ventricular tachycardia. A patient-specific phenomenon.

The purpose of our study was to investigate the electrical trigger modes of monomorphic ventricular tachycardia, by analysing stored intracardiac electrograms, and to identify haemodynamic or electrocardiographic predictors in patients with cardioverter-defribrillators. We recorded 286 episodes of monomorphic ventricular tachycardia in 38 patients with at least three events. The electrical triggers were characterized by the morphology number, complexity, and coupling interval of premature depolarizations preceding the ventricular tachycardia. We also evaluated clinical and electrocardiographic data. We found two basic electrical trigger modes. Two hundred and sixteen events (75%) were observed to have no RR-interval variations before onset, while 70 episodes (25%) had a short-long-short sequence. These episodes invariably featured increased QT disperson. In 31 of 38 patients (82%), the ventricular tachycardias were always initiated by the same mode of onset. In eight patients, the monomorphic ventricular tachycardias were always triggered by short-long-short sequences. In seven patients, more than one onset mechanism was observed. Two basic modes of onset were responsible for monomorphic ventricular tachycardia: one without RR-interval variations immediately prior to onset and another characterized by short-long-short sequences and increased QT dispersion. The mechanisms were largely patient-specific and not related to cardiac diagnosis or left ventricular function.

Spectral analysis of electrograms during ventricular tachycardia in a canine model: Relation with epicardial isochronal maps

The purpose of this study was to assess the capability of magnitude-squared coherence and bicoherence to differentiate monomorphic ventricular tachycardia (MVT) and polymorphic ventricular tachycardia (PVT) in a canine model and to relate these results to the epicardial isochronal maps on a beat-to-beat basis. Unipolar electrograms were simultaneously recorded from the surface of both ventricles with a 127-lead sock electrode array in 12 open-chest anesthetized dogs. The sampling frequency was 500 Hz. Atrioventricular block was induced by formaldehyde injection into the atrioventricular node. The left anterior descending coronary artery was occluded for 60 minutes under ventricular pacing (140 beats/min). During reperfusion, 12 MVT episodes lasting more than 42 seconds were recorded. Left stellate ganglion stimulation induced five PVT episodes lasting more than 42 seconds. Each of these recordings was divided into seven segments of 3,072 points (6.144 seconds). After visual selection, 104 segments were extracted and classified as 73 MVT and 31 PVT segments. Magnitude-squared coherence was estimated as the cross-spectrum from two epicardial signals (on the right and left ventricles, respectively), normalized with the respective autopower spectrum. Bicoherence was estimated as the bispectrum normalized with the autopower spectrum. Magnitude-squared coherence correctly identified 96% of MVT. and 81% of PVT segments for a total accuracy of 91%. Bicoherence estimated with the left ventricular lead correctly identified 100% of MVT and 77% of PVT segments with an accuracy of 93%. Beat-to-beat epicardial maps of MVT displayed a cluster of sites of origin close to the reperfusion area, while the sites of origin from beats during PVT were much more dispersed over both ventricles. A strong and significant correlation was found between the number of electrodes with the earliest epicardial activation and coherence ( r = .76, P < .0001) and bicoherence ( r = .68, P < .0001), respectively. A high and significant correlation was also found between both spectral estimators ( r = .74, P < .0001). Coherence and bicoherence discriminated accurately between MVT and PVT. Coherence achieved better results compared with bicoherence. Coherence and bicoherence measurements showed a quantitative relation with the spatial dispersion of the sites of origin. Both spectral techniques seemed powerful enough to be used in the development of implantable devices.

Percutaneous multielectrode endocardial mapping during ventricular tachycardia in the swine model.

Identification of critical areas within the ventricular tachycardia circuit is a prerequisite for catheter ablation. Currently, mapping during ventricular tachycardia, usually performed with standard catheters, is difficult and time-consuming and can be used only in patients with hemodynamically stable tachycardia. A total of 43 pigs underwent closed-chest induction of myocardial infarction. A basket-shaped catheter carrying 64 electrodes was deployed in the left ventricle during normal sinus rhythm. Unipolar pacing at 3 mA was successful in 78% of the basket catheter electrodes, demonstrating good electrode-tissue contact. Hemodynamic and echocardiographic measurements did not reveal any significant interference with myocardial or valvular function during or after catheter deployment. One hundred eighteen episodes of monomorphic ventricular tachycardia were induced in 28 pigs through right ventricular stimulation, 81 of which were mapped and analyzed. Ventricular tachycardia mapping was rapid, requiring only several beats and < 10 seconds to complete. Presystolic potentials, a possible target for ablation, were identified in 58% of the tachycardia episodes mapped. Pathological examination revealed only minor valvular and endocardial catheter-induced lesions immediately after mapping and none a month later. The multielectrode catheter enables rapid and safe percutaneous endocardial mapping of ventricular tachycardia in the swine model. Exploration of the clinical potential of the multielectrode catheter seems warranted.

Stability: an ICD detection criterion for discriminating atrial fibrillation from ventricular tachycardia.

The purpose of this study was to review a new implantable cardioverter defibrillator (ICD) detection criterion, stability, to determine if it can effectively discriminate rapid rhythms of atrial fibrillation from ventricular tachycardia. Inappropriate shocks for rapid atrial fibrillation limit the acceptance of ICDs. The advent of an additional detection criterion, stability, has been postulated to be of value in discriminating rapid atrial fibrillation, which may not warrant treatment, from ventricular tachycardia, which obviously does warrant therapy deliver. Twenty-six patients were studied during 32 episodes of rapid atrial fibrillation and 24 episodes of monomorphic ventricular tachycardia below 220 beats/min. Each rhythm was repeatedly evaluated by the device at each of the seven stability values available (8, 16, 23, 31, 39, 47, and 55 msec) and then classified as stable or unstable. Upon completion of this acute study, 32 ICD patients had the stability feature activated and were followed for proper arrhythmia treatment by the device. Using stability windows from 8 to 47 msec, all atrial fibrillation rhythms were appropriately classified as unstable. Three of 6 were classified correctly for the 55-msec window. All ventricular tachycardia rhythms were appropriately classified as stable from all stability windows from 8 to 55 msec. Clinical follow-up confirmed appropriate therapy delivery when coupled with sustained rate duration (SRD). Thirty-two patients followed for 292 patient-months had no episodes of untreated ventricular tachycardia with 428 successfully classified as stable and treated. Only three episodes of suspected atrial fibrillation resulted in therapy delivery as the rhythm duration exceeded the SRD of 30 seconds. The CPI Ventak PRx ICD is highly reliable in appropriately classifying atrial fibrillation as unstable and monomorphic ventricular tachycardia as stable for most stability windows evaluation tachycardias below 220 beats/min. As a result, when testing of atrial fibrillation is not possible, we recommend the routing programming of this stability feature at the 31-msec window with an SRD of 30 seconds. The reliability of this device in discriminating atrial fibrillation from monomorphic ventricular tachycardia may have important clinical implications for other tiered therapy ICDs with this feature as well as for future ICDs in development.

Ventricular Arrhythmias Detected After Transvenous Defibrillator Implantation in Patients With a Clinical History of Only Ventricular Fibrillation

Patients with a history of ventricular fibrillation (VF) have been shown to have a clinical profile, response to electrophysiological testing (EPS), and response to antiarrhythmic therapy that distinguishes them from patients with a history of sustained monomorphic ventricular tachycardia (MVT). Despite these differences, it is not clear whether VF in these patients is triggered by MVT or occurs de novo. The incidence of MVT and VF in such patients after their index VF event has important implications for therapeutic decisions regarding implantable defibrillator selection and programming. The records of 111 consecutive patients who had undergone transvenous cardioverter/defibrillator (ICD) implantation for malignant ventricular arrhythmias were reviewed retrospectively. For each patient, all device tachyarrhythmia detections were examined and classified as VF, MVT, rapid polymorphic VT, or other. The number of events, time to first arrhythmia detection, and cycle length of MVTs were recorded. There were 55 patients with a history of only VF and 56 with a history that included an episode of MVT. Over 14 months of follow-up, with all patients initially off of antiarrhythmic medications, MVT was detected by only 18% of patients with a history of only VF compared with 54% of those with a history that included MVT (P = .002). Among patients who did detect MVT, those with a history of only VF had fewer episodes (7 +/- 7 versus 20 +/- 31, P = .001) and a shorter mean MVT cycle length (279 versus 314 ms, P = .03) than those with a clinical history of MVT. Abrupt onset of VF not preceded by MVT was detected in 11% of patients with VF only. In addition to a history of MVT, male sex, age < 60 years, and MVT inducible on EPS were all significantly associated with an increased likelihood of MVT detection. On multivariate analysis, the inducibility of MVT was the primary independent predictor of MVT detection but was of minimal incremental predictive value in the subgroup of patients with a history of only VF. When EPS results were not considered, arrhythmia history was the primary independent predictor of MVT detection. Patients with a history of only VF infrequently have MVT detected by their defibrillators. When these patients do detect MVT, it is faster than that detected in patients with a clinical history of MVT before ICD surgery. A significant percentage of VF survivors detected the abrupt onset of VF not preceded by MVT, suggesting that the deterioration of rapid MVT to VF is not the only clinically important mechanism of VF induction. These findings may have important implications for the understanding of the mechanism of VF induction and for use of an implantable defibrillator.

Radiofrequency Catheter Ablation of Ventricular Tachycardia Following Implantation of an Automatic Cardioverter Defibrillator

The present study reports on the complementary role of two nonpharmacological options of antiarrhythmic therapy. Catheter ablation, antitachycardia surgery, and the implantable cardioverter defibrillator (ICD) have become important tools in the management of ventricular tachyarrhythmias. However, the emergence of ventricular tachyarrhythmias after implantation of an ICD is possible because the arrhythmogenic substrate is not affected. Six of 180 patients developed frequent episodes of monomorphic ventricular tachycardia (n = 2) or incessant ventricular tachycardia (n = 4) following implantation of an ICD and underwent radiofrequency (RF) catheter ablation. Catheter ablation was performed using a RF generator HAT 200. Energy was delivered between a 4-mm tip electrode of the ablation catheter and a patch electrode. Catheter ablation was done 6.8 +/- 5 months following ICD implantation; 6 +/- 2.2 RF impulses were delivered at the site of origin of ventricular tachycardia characterized by early endocardial activation during ventricular tachycardia, identical pace mapping and long latency between stimulus, and QRS-complex in five patients. New bundle branch reentry was the underlying mechanism of ventricular tachycardia in one patient. RF catheter ablation resulted in termination of incessant ventricular tachycardia. Immediately postablation, the documented ventricular tachycardia was rendered noninducible in all patients. No ICD malfunctions have been observed. One patient died due to heart failure 24 hours after successful ablation of the incessant ventricular tachycardia. During a follow-up of 5-19 months, episodes of ventricular tachycardia recurred in four patients. All episodes could be controlled by the ICD without frequent cardioversions. RF catheter ablation is a complementary therapeutic option in case of frequent or incessant ventricular tachycardia after ICD implantation.

Epicardial activation patterns of torsade de pointes in canine hearts with quinidine-induced long QT interval but without myocardial infarction

We studied the epicardial activation sequence during torsade de pointes in canine hearts with quinidine-induced long QT interval. Following a toxic dose of quinidine sulfate (30 mg/kg), polymorphic ventricular tachycardia was induced by extrastimuli. In nine dogs, 22 episodes of nonsustained polymorphic ventricular tachycardia and six episodes of monomorphic ventricular tachycardia were induced. Of 22 episodes of nonsustained polymorphic ventricular tachycardia, 12 episodes showed typical torsion of the spikes of the QRS complex around the isoelectric line (torsade de pointes). Isochronal maps were made from 38 simultaneously recorded bipolar electrograms and showed that each change in QRS morphology was associated with a change in the earliest epicardial activation site and/or a change of epicardial activation sequence. During episodes of torsade de pointes, the earliest epicardial activation site migrated gradually from one site to another site. The transitional QRS complexes had their earliest epicardial activation sites between the new and old site of the earliest epicardial activation. The changes in the earliest epicardial activation site during polymorphic ventricular tachycardia without torsade de pointes pattern was not as great as that noted during torsade de pointes. This study suggests that in a noninfarcted canine model torsade de pointes is produced by alteration in the earliest site of activation rather than by competition from two or more competing foci.

Identification of reproducible ventricular tachycardia in a canine model

Epicardial mapping was used as a standard to investigate how well the limb leads, both alone and in conjunction with 5 select epicardial electrodes, can verify reproducibility in a common, open-chest canine model of ventricular tachycardia (VT). Reproducible VT was defined as 2 or more episodes of monomorphic VT with similar rates, limb lead tracings and epicardial maps. In this study, 21 dogs underwent 2-hour occlusion of the left anterior descending coronary artery followed by reperfusion. Three days later, programmed stimulation was used to induce VT that was analyzed with limb leads I, II and III and 27 simultaneously recorded, bipolar epicardial electrodes. Thirteen dogs had VT of which 11 had polymorphic VT (varying QRS morphology). Twelve dogs yielded at least 1 form of monomorphic VT. Eight had 2 or more distinct forms of monomorphic VT (pleomorphism). Four of these 8 dogs had pleomorphic VT that was not apparent from the limb lead tracings, but was recognized from the epicardial activation maps constructed from the 27 epicardial recordings. To provide a method of distinguishing various VTs without the need of full epicardial mapping, 5 of the 27 epicardial electrodes were selected. These were postitioned over the midanterior and midposterior right and left ventricles, and the left ventricular apex. By analyzing electrogram morphology and activation time, VT reproducibility could be as accurately identified with these 5 electrodes as with epicardial mapping derived from 27 electrodes. In conclusion, multiple VT morphologies are common in this open-chest canine model. Limb lead recordings alone are inadequate for analysis of VT reproducibility. The limb leads in conjunction with 5 select epicardial electrodes can verify VT reproducibility as well as 27-electrode epicardial maps.