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Late potentials on signal-averaged electrocardiography eliminated by successful catheter ablation of premature ventricular contractions in a nonischemic cardiomyopathy patient
Address reprint requests and correspondence: Dr Masafumi Sugawara, Department of Cardiovascular Medicine, Chiba University Graduate School of Medicine, 1-8-1 Inohana, Chuo-ku, Chiba, 260-8670, Japan.
The signal-averaged electrocardiogram (SA-ECG) is a noninvasive diagnostic tool to evaluate the risk of future sudden cardiac death, especially in patients with ischemic cardiomyopathy.
Late potentials (LPs) are subtle cardiac electrical abnormalities detected by the SA-ECG, which reflects an arrhythmogenic substrate in a diseased myocardium. However, for about 4 decades, the clinical beneficial evidence of the SA-ECG in patients with nonischemic cardiomyopathy (NICM) such as dilated cardiomyopathy (DCM) has not yet been established. We hereby present a case in which nocturnal LPs were eliminated and the SA-ECG findings were normalized after successful catheter ablation of premature ventricular contractions (PVCs) in a patient diagnosed with DCM.
Key Teaching Points
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The signal-averaged electrocardiogram (SA-ECG) is a noninvasive tool to stratify the future risk of fatal arrhythmias or sudden cardiac death in structural heart disease, while late potentials (LPs) are an abnormal finding recorded by the SA-ECG and represent slow conduction areas derived from slow conduction within myocardial scar.
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In this present dilated cardiomyopathy case, although nocturnal LPs were clearly recorded before ablation, they were eliminated completely after the ablation of premature ventricular contractions.
•
The evidence from the SA-ECG on nonischemic cardiomyopathy is still ambiguous because of its pathophysiological heterogeneity. However, this case report indicated that the SA-ECG could potentially evaluate the efficacy of ventricular arrhythmia ablation and makes us reconsider its utility.
Case report
A 40-year-old Japanese man with a history of DCM and a secondary prophylactic implantable cardioverter-defibrillator (ICD) implantation was admitted following ventricular fibrillation (VF) aborted by an appropriate ICD shock therapy (Figure 1A). A 12-lead electrocardiogram showed 2 kinds of PVCs (Figure 1B). One PVC (PVC1) exhibited a left bundle branch block configuration and a superior axis QRS morphology with a late transition (> lead V3) and maximum deflection index of 0.51. The other one (PVC2) exhibited a left bundloid configuration and superior axis QRS morphology with an early transition (< lead V3) and maximum deflection index of 0.47. On echocardiography, the left ventricular ejection fraction was 29% on optimal medical therapy. An ICD interrogation revealed that a PVC triggered the VF (Figure 1C). Actually, this was his second episode of an appropriate ICD shock event. One year prior, he had experienced a similar VF episode; at that time he had already been prescribed 160 mg of d-sotalol and 20 mg of carvedilol (maximum dose in Japanese guideline). Nevertheless, he had a repeated episode of VF, and on top of that, 24-hour Holter monitoring documented a high burden of PVCs (29% per total heartbeats). Based on the future risk of recurrence and drug-resistant lethal arrhythmias, we performed catheter ablation of the PVCs.
Figure 1A: An implantable cardioverter-defibrillator interrogation revealing ventricular fibrillation aborted by a 36 J shock therapy. B: A 12-lead electrocardiogram recorded during an atrial paced rhythm showing 2 kinds of premature ventricular contractions (PVC) of which the coupling intervals are similar. C: Ventricular fibrillation (VF) induced by a bigeminal PVC at midnight. The red arrows highlight the triggered PVC, inducing VF.
The procedure was conducted under local anesthesia and sotalol was continued during the periprocedural period. We accessed the left ventricle via a transseptal puncture using an 8.5F steerable sheath (Agilis; Abbott, St. Paul, MN). Electroanatomical mapping was guided by a 3-dimensional mapping system (EnSiteX; Abbott, St. Paul, MN). A local activation map acquired using a flat multipolar catheter (Advisor HD Grid; Abbott, St. Paul, MN) exhibited both PVC1 and PVC2 that originated from the inferior interventricular septum, while far-field prepotentials were favorably recorded from both the right and the left ventricle, and fractionated delayed potentials were recorded within the normal sinus QRS complexes preceding the PVC beat (Figure 2A). Based on the similar coupling intervals and prior cardiac magnetic resonance imaging (MRI) showing an intramural late gadolinium enhancement on the basal septum (Figure 2B), we hypothesized that the same origin harbored different myocardial breakthroughs into the right ventricle (PVC1) and into the left ventricle from the same origin (PVC2). Radiofrequency current was applied on the septal epicenter at 30 W from both ventricles, which eliminated both PVC1 and PVC2. On the other hand, the patient was still susceptible to mechanical stimulation, so a short VF was inducible. Endocardial voltage mapping of the left ventricle identified 2 focalized low-voltage sites at the anterior and inferior aspects (Figure 2C). Although VF was induced by mechanical catheter stimulation in those areas, radiofrequency current applications at those sites reduced the inducibility of fibrillatory activity. The procedure was concluded without any complications.
Figure 2A: The intracardiac electrograms recorded by an HD Grid mapping catheter (Abbott, St. Paul, MN) on both the right and left interventricular septum that exhibited favorable prepotentials preceding the onset of the QRS complex by 46 ms and 71 ms, respectively. Note that a fractionated delayed potential is recorded within the normal sinus QRS complex preceding the premature ventricular contraction (PVC) beat. B: Past cardiac magnetic resonance imaging depicting late gadolinium enhancement in the intramural myocardium of the basal mid wall. C: Left ventricular voltage mapping and ablation sites. Except for the focalized ablation sites, the left ventricle voltage is relatively preserved.
After discharge, his 24-hour Holter monitoring (FM-1500; Fukuda Denshi Co, Ltd, Tokyo, Japan) documented a reduced PVC burden (0.3% per total heartbeats). The SA-ECG analysis in the same setting before and after the ablation (XYZ lead position, sampling every 60 minutes, bandpass filter: 40∼300 Hz, noise level: under 40 μV) showed that although a positive LP with a circadian variation was initially recorded on the 24-hour SA-ECG (Figure 3A), the nocturnal abnormal finding of the SA-ECG became completely negative the entire day after the catheter ablation (Figure 3B). An improvement was observed in all 3 parameters of the SA-ECG, consisting of the filtered QRS (fQRS) duration, duration of low-amplitude signals <40 mV (LAS40), and amplitude of root mean square voltage of the terminal 40 ms in the fQRS complex (RMS40). The improvement after the ablation was predominant at midnight, and the LP apparently disappeared during that time period (Figure 3C). During a 9-month follow-up after discharge, the patient has been free from any lethal arrhythmic events and ICD therapies.
Figure 3A: An initial evaluation of the signal-averaged electrocardiogram (SA-ECG). Late potentials (LPs) are considered positive if at least 2 of the following criteria are met: (1) filtered QRS duration (fQRSd) ≥120 ms, (2) root mean square voltage of the terminal 40 ms in the fQRS complex (RMS40) <20 mV, and (3) low-amplitude signals <40 mV (LAS40) >38 ms. For each component, it met the criteria expressed by the red dots. The positive late potentials are highlighted by a red square. B: The normalized SA-ECG measured a few months after the premature ventricular contraction (PVC) ablation. C: Comparison of the SA-ECG showing the eliminated late potential highlighted by the red arrow. Upper panel: An abnormal SA-ECG before the ablation procedure. Lower panel: A normalized SA-ECG after the PVC ablation evaluated in the same time zone.
To our knowledge, this is the first case report presenting a dynamic change in the SA-ECG after a PVC ablation in an NICM patient. The SA-ECG is a noninvasive diagnostic tool to stratify the ventricular arrhythmic risks in patients with organic heart disease.
LPs are the terminal portion of the averaged QRS complex recorded by the SA-ECG and are considered to represent a substrate of delayed conduction due to a myocardial abnormality. Especially in ischemic cardiomyopathy (ICM) patients, the utility of the SA-ECG has been well established for several decades.
Additionally, in recent years, it has been reported that an improvement in an abnormal SA-ECG after ventricular tachycardia (VT) ablation is associated with a lower risk of VT recurrence and mortality.
Signal-averaged electrocardiography as a noninvasive tool for evaluating the outcomes after radiofrequency catheter ablation of ventricular tachycardia in patients with ischemic heart disease: reassessment of an old tool.
Dynamic changes in the signal-averaged electrocardiogram are associated with the long-term outcomes after ablation of ischemic ventricular tachycardia.
In these articles, the authors mentioned that substrate modification contributes to the elimination of the LPs. They also concluded that normalization of the SA-ECG could be an adjunctive marker to predict procedural success after ablation in ICM patients.
On the other hand, compared to ICM, the utility of the SA-ECG in NICM patients has not been established. While Fauchier and colleagues
mentioned that LPs on the SA-ECG are an independent predictor of all-cause cardiac mortality in NICM patients, other reports have shown no significant difference in the presence of LPs.
The signal-averaged electrocardiogram is of limited value in patients with bundle branch block and dilated cardiomyopathy in predicting inducible ventricular tachycardia or death.
Differentiation of heart failure related to dilated cardiomyopathy and coronary artery disease using gadolinium-enhanced cardiovascular magnetic resonance.
Endocardial and epicardial radiofrequency ablation of ventricular tachycardia associated with dilated cardiomyopathy: the importance of low-voltage scars.
Nonischemic fibrosis is pathologically smaller than an infarct area and transmurally scattered in the ventricle. Thus, fibrotic areas in NICM sometimes exist in the epicardial region more than the endocardial region or are focalized in the intramural area. Additionally, delayed activity in the endocardium and epicardium recorded during the ablation procedure are observed less frequently in NICM cases than in ICM cases.
Characterization of the arrhythmogenic substrate in ischemic and nonischemic cardiomyopathy implications for catheter ablation of hemodynamically unstable ventricular tachycardia.
Outcomes in catheter ablation of ventricular tachycardia in dilated nonischemic cardiomyopathy compared with ischemic cardiomyopathy: results from the Prospective Heart Centre of Leipzig VT (HELP-VT) Study.
Substrate-guided ablation of haemodynamically tolerated and untolerated ventricular tachycardia in patients with structural heart disease: effect of cardiomyopathy type and acute success on long-term outcome.
and also generate the longtime controversy over the utility of the SA-ECG.
In this case, both PVC1 and PVC2 had opposite direction in aVR and aVL, and QRS polarity in aVR was negative. From these characteristics, PVCs were deemed to be derived from close to the base of ventricle and from the septum.
This origin was consistent with the result of cardiac MRI and successful ablation site. As shown in the MRI and voltage mapping during the ablation procedure, the arrhythmogenic substrate seemed to be relatively focalized in specific segments of the left ventricle, while the origin of the PVC was isolated in the surrounding healthy myocardium. These facts may have led to the significant elimination of LPs after a successful ablation. Dinov and colleagues
Dynamic changes in the signal-averaged electrocardiogram are associated with the long-term outcomes after ablation of ischemic ventricular tachycardia.
suggested a significant correlation between the surface area of the endocardial scar and filtered QRS duration. Although this previous report was regarding ICM patients, a significant volume of fibrotic scar may lead to positive surface LPs even in NICM. We would also like to emphasize the circadian change in the SA-ECG. If one is available, it is recommended to use a continuous monitoring device to elucidate such LPs.
Conclusion
We presented an NICM case in which LPs recorded on the SA-ECG were successfully eliminated after the ablation of PVCs originating from an intramural scar area. Although its evidence has not been well established, our case may indicate that the SA-ECG could be a potentially useful tool to evaluate the effectiveness of a therapy after ventricle arrhythmia ablation in patients harboring LPs and confined abnormal myocardium. In order to establish more solid evidence, a larger population and unified validation are necessary.
Acknowledgments
We thank Mr John Martin for his linguistic assistance regarding this report.
References
Kuchar D.L.
Thorburn C.W.
Sammel N.L.
Late potentials detected after myocardial infarction: natural history and prognostic significance.
Signal-averaged electrocardiography as a noninvasive tool for evaluating the outcomes after radiofrequency catheter ablation of ventricular tachycardia in patients with ischemic heart disease: reassessment of an old tool.
Dynamic changes in the signal-averaged electrocardiogram are associated with the long-term outcomes after ablation of ischemic ventricular tachycardia.
The signal-averaged electrocardiogram is of limited value in patients with bundle branch block and dilated cardiomyopathy in predicting inducible ventricular tachycardia or death.
Differentiation of heart failure related to dilated cardiomyopathy and coronary artery disease using gadolinium-enhanced cardiovascular magnetic resonance.
Endocardial and epicardial radiofrequency ablation of ventricular tachycardia associated with dilated cardiomyopathy: the importance of low-voltage scars.
Characterization of the arrhythmogenic substrate in ischemic and nonischemic cardiomyopathy implications for catheter ablation of hemodynamically unstable ventricular tachycardia.
Outcomes in catheter ablation of ventricular tachycardia in dilated nonischemic cardiomyopathy compared with ischemic cardiomyopathy: results from the Prospective Heart Centre of Leipzig VT (HELP-VT) Study.
Substrate-guided ablation of haemodynamically tolerated and untolerated ventricular tachycardia in patients with structural heart disease: effect of cardiomyopathy type and acute success on long-term outcome.
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