Advertisement

Hourly variability versus ECG morphological criteria in predicting the site of origin of ventricular outflow tract ectopy

Open AccessPublished:January 10, 2023DOI:https://doi.org/10.1016/j.hrcr.2023.01.001

      Keywords

      Key Teaching Points
      • The location of ventricular arrhythmias in the outflow tracts based on morphological criteria may be ineffective in certain patients.
      • In patients with cardiac rotation, the location of the arrhythmia may be more limited with only morphological criteria.
      • The hourly variability of the ventricular arrhythmic events seems to be a good tool to locate these arrhythmias.

      Introduction

      Outflow tract ventricular arrhythmias (OTVA) are the most common form of idiopathic ventricular arrhythmias encountered in clinical practice. The 12-lead electrocardiogram (ECG) is a vitally important tool that allows rapid and noninvasive localization of the most likely site of origin (SOO) when planning ablation procedures. Different ECG criteria have been validated for this purpose.
      • Park K.M.
      • Kim Y.H.
      • Marchlinski F.E.
      Using the surface electrocardiogram to localize the origin of idiopathic ventricular tachycardia.
      However, their accuracy may be reduced by variations in body habitus and cardiac orientation.
      • Yoshida N.
      • Inden Y.
      • Uchikawa T.
      • et al.
      Novel transitional zone index allows more accurate differentiation between idiopathic right ventricular outflow tract and aortic sinus cusp ventricular arrhythmias.
      Recently, our group published a new algorithm based on the variability of arrhythmic events over a 24-hour period rather than QRS morphology.
      • Waight M.C.
      • Li A.C.
      • Leung L.W.
      • et al.
      Hourly variability in outflow tract ectopy as a predictor of its site of origin.
      This case report illustrates its practical applicability.

      Case report

      A 40-year-old woman with no relevant medical history presented with palpitations during the second trimester of pregnancy caused by ventricular ectopy (VE) and runs of nonsustained monomorphic ventricular tachycardia (NSVT) of outflow tract origin. Her heart was structurally normal on echocardiography. She was treated with metoprolol 25 mg twice a day, which suppressed the ectopy for the remainder of the pregnancy. However, a subsequent 24-hour Holter monitor on beta-blocker therapy still showed a moderate VE burden of 4% with some runs of NSVT of identical morphology and with significant accompanying symptoms in the form of palpitations mainly. The VE showed an atypical right bundle branch block morphology, right inferior axis, and V2–V3 transition on the 12-lead ECG (Figure 1A). She was therefore referred for catheter ablation. The ECG morphology of the VE was assessed and measured before ablation using the electronic calipers in the recording system at 25 mm/s speed and a standard gain of 1 mV/cm with a filter setting of 0.05 Hz (high pass) and 100 Hz (low pass) (C.R. Bard, Inc, Lowell, MA). The most widely used criteria for localizing OTVA SOO pointed to the left side as the most likely origin. However, the recently published criteria, based on the behavior of the ectopy over a 24-hour period, determined the origin to be on the right side. Specifically, the CoV (standard deviation divided by mean) was 2.5, higher than the cut-off of 0.7, and the presence of any hour with less than 50 VEs, another even more sensitive and specific determinant, also pointed to a right-sided SOO (Table 1).
      • Waight M.C.
      • Li A.C.
      • Leung L.W.
      • et al.
      Hourly variability in outflow tract ectopy as a predictor of its site of origin.
      Figure thumbnail gr1
      Figure 1A: Twelve-lead electrocardiogram (ECG) with the ectopic beats. B: Left anterior oblique projection at 75º. C: Initial activation map of the right ventricular outflow tract and lesion set during the first procedure. D: Twelve-lead ECG with the ectopic beat during the second procedure. E: Activation map showing the earliest activity in the left cusp of the pulmonary valve and the ablation lesions at this site. F: Right anterior oblique projection during ablation in the left cusp of the pulmonary valve with catheter in reverse U position. G: Endocavitary signals with the bipolar and unipolar electrograms at the earliest site. H: Final set of ablation lesions located above and below the pulmonary valve.
      Table 1Criteria described to predict the site of origin of outflow tract ectopy
      AlgorithmValueSOO predictionPredictive value
      R-wave duration index
      • Ouyang F.
      • Fotuhi P.
      • Ho S.Y.
      • et al.
      Repetitive monomorphic ventricular tachycardia originating from the aortic sinus cusp: electrocardiographic characterization for guiding catheter ablation.
      0.57LVOTSe 88%Sp 95%
      R/S-wave amplitude index
      • Ouyang F.
      • Fotuhi P.
      • Ho S.Y.
      • et al.
      Repetitive monomorphic ventricular tachycardia originating from the aortic sinus cusp: electrocardiographic characterization for guiding catheter ablation.
      0.66LVOTSe 88%Sp 95%
      V2S/V3R index
      • Yoshida N.
      • Yamada T.
      • McElderry H.T.
      • et al.
      A novel electrocardiographic criterion for differentiating a left from right ventricular outflow tract tachycardia origin: the V2s/V3R index.
      1.20LVOTSe 89%Sp 94%
      TZ index
      • Yoshida N.
      • Inden Y.
      • Uchikawa T.
      • et al.
      Novel transitional zone index allows more accurate differentiation between idiopathic right ventricular outflow tract and aortic sinus cusp ventricular arrhythmias.
      -3LVOTSe 88%Sp 82%
      S-R amplitude difference
      • Kaypakli O.
      • Koca H.
      • Sahin D.Y.
      • Karataş F.
      • Ozbicer S.
      • Koç M.
      S-R difference in V1-V2 is a novel criterion for differentiating the left from right ventricular outflow tract arrhythmias.
      0.38LVOTSe 95%Sp 85%
      Minimum hourly VEs
      • Waight M.C.
      • Li A.C.
      • Leung L.W.
      • et al.
      Hourly variability in outflow tract ectopy as a predictor of its site of origin.
      <50RVOTSe 96%Sp 94%
      CoV
      • Waight M.C.
      • Li A.C.
      • Leung L.W.
      • et al.
      Hourly variability in outflow tract ectopy as a predictor of its site of origin.
      2.50RVOTSe 78%Sp 94%
      LVOT = left ventricular outflow tract; RVOT = right ventricular outflow tract; Se = Sensitivity, SOO = Site of origin, Sp = Specificity, TZ = transition zone; VE = Ventricular ectopy.
      An electrophysiology study to map and ablate the VE under local anesthesia was performed. Frequent, spontaneous VE was noted at baseline without any form of stimulation. Following femoral venous access, a decapolar catheter was placed in the coronary sinus (CS) up to the junction of the great cardiac vein and the anterior interventricular vein. A marked clockwise rotation of the heart was obvious with the true left anterior oblique projection at 75º (Figure 1B). Pace mapping was performed from the distal CS bipole with less than 90% match. Right ventricular outflow tract (RVOT) activation mapping was performed using a mapping/ablation catheter (ThermoCool SmartTouch SF; Biosense Webster, Diamond Bar, CA) via an 8.5F long sheath and the 3-dimensional electroanatomical mapping system (CARTO; Biosense Webster, Diamond Bar, CA). The earliest myocardial activation pre-QRS (-25 ms) was located in the anteroseptal wall, immediately below the pulmonary valve (PV) (Figure 1C). Good pace mapping, matching between 95% and 98%, was demonstrated in this area. Brief additional mapping of the aortic root and the left ventricular outflow tract, via retrograde transaortic approach, showed late, far-field activation and less than 90% match on pace mapping. Radiofrequency (RF) energy was applied at 30 W at the earliest RVOT activation site. This induced more ectopy and some runs of NSVT identical to the clinical VE. However, definitive abolition of the ectopy was not achieved despite a series of lesions in the entire target area. Therefore, more extensive mapping of the anteroseptal RVOT and above the PV was carried out, showing bipolar signals with significantly earlier activation (-40 ms pre-QRS) during ectopy and excellent unipolar electrograms. This area located above the PV, with only far-field low-voltage electrograms in sinus rhythm, also showed an excellent pace map with a 99% match and its subsequent ablation led to the disappearance of VE within 10–15 seconds. To perform the ablation in this area, we did not perform prior coronary angiography, but we used a maximum of 30 W of RF energy for 30–60 seconds, with careful ECG monitoring. Consolidation lesions were delivered surrounding the first lesion at the level of the PV. The procedure concluded 25 minutes later, with the ectopy remaining noninducible despite aggressive stimulation with burst ventricular pacing and isoprenaline infusion at a dose of 4 mcg/min.
      However, 1 month later, the patient presented with recurrent symptoms and the repeat 24-hour Holter showed a VE burden of 10% of the same previous morphology (Figure 1D). A new ablation procedure was performed, mapping with the CARTO system and a multielectrode catheter (PentaRay; Biosense Webster, Diamond Bar, CA). The PentaRay catheter–induced ectopy at the anteroseptal RVOT that was identical to the clinical VE and the activation mapping of the spontaneous ectopy confirmed the exit site to be in close proximity, just above the PV. The left ventricular outflow tract was briefly mapped once again, showing late activation, as well as the distal CS catheter at the great cardiac vein–anterior interventricular vein junction, both sites producing pace maps with <90% match. As the PentaRay catheter could not be positioned above the PV and curved down into the pulmonic cusp, it was replaced with the ablation catheter (ThermoCool SmartTouch SF; Biosense Webster), which was advanced up to the pulmonary artery, curved down (reverse U fashion), and brought to the level of the PV. The earliest local activation (-40 ms) was found at the level of the left cusp of the PV (Figure 1E and 1F). RF ablation at 30 W in this area induced NSVT identical to the clinical VE, which disappeared during the first lesion. Subsequent RF ablation at the adjacent RVOT at the subvalvular level was performed at all the neighboring sites with precocity (Figure 1G). No new VE appeared during a 30-minute waiting period and the procedure was concluded. Overnight telemetry showed no further ectopy. At follow-up, the patient has been symptom-free and the Holter at 3 months showed 0% ectopy.

      Discussion

      Idiopathic ventricular arrhythmias originate preferentially in the outflow tract areas of both ventricles. Current imaging techniques have made it possible to improve the understanding of these 2 closely related structures, allowing catheter ablation to be an effective and safe option for long-term control. However, careful preprocedural 12-lead analysis is important in localizing ectopic activity and procedural planning. Specifically, predicting ectopy SOO before the procedure can help identify the correct access and optimal ablation strategy, reducing risks, complications, and procedural duration.
      Because idiopathic OTVA have a focal origin and occur in patients with a structurally normal heart, it is an arrhythmia that is particularly conducive to localization by ECG. For this reason, during the past decades, different morphology-based criteria have been proposed to differentiate left from right SOO.
      • Ouyang F.
      • Fotuhi P.
      • Ho S.Y.
      • et al.
      Repetitive monomorphic ventricular tachycardia originating from the aortic sinus cusp: electrocardiographic characterization for guiding catheter ablation.
      • Yoshida N.
      • Yamada T.
      • McElderry H.T.
      • et al.
      A novel electrocardiographic criterion for differentiating a left from right ventricular outflow tract tachycardia origin: the V2s/V3R index.
      • Betensky B.P.
      • Park R.E.
      • Marchlinski F.E.
      • et al.
      The V2 transition ratio: a new electrocardiographic criterion for distinguishing left from right ventricular outflow tract tachycardia origin.
      • Kaypakli O.
      • Koca H.
      • Sahin D.Y.
      • Karataş F.
      • Ozbicer S.
      • Koç M.
      S-R difference in V1-V2 is a novel criterion for differentiating the left from right ventricular outflow tract arrhythmias.
      However, these parameters can be complex and are influenced by variations in the 3-dimensional anatomical relationship of the outflow tracts, meaning that subtle variationsin the position of the surface ECG electrodes or cardiac orientation can alter the surface QRS morphology, both of the sinus and ectopic beats.
      • Anter E.
      • Frankel D.S.
      • Marchlinski F.E.
      • Dixit S.
      Effect of electrocardiographic lead placement on localization of outflow tract tachycardias.
      ,
      • Tahara Y.
      • Mizuno H.
      • Ono A.
      • Ishikawa K.
      Evaluation of the electrocardiographic transitional zone by cardiac computed tomography.
      Parameters developed in an attempt to correct for cardiac rotation, such as the transitional zone index, correct some but not all of these limitations.
      • Yoshida N.
      • Inden Y.
      • Uchikawa T.
      • et al.
      Novel transitional zone index allows more accurate differentiation between idiopathic right ventricular outflow tract and aortic sinus cusp ventricular arrhythmias.
      We recently published nonmorphological criteria, based on the behavior of OTVA over a 24-hour period, demonstrating that they can predict the SOO with a high degree of precision. Specifically, it was observed that the presence of any hour with VE <50 is highly suggestive of SOO in the RVOT, as well as a high variability with a CoV ≥0.7.
      • Waight M.C.
      • Li A.C.
      • Leung L.W.
      • et al.
      Hourly variability in outflow tract ectopy as a predictor of its site of origin.
      It was hypothesized that this could be related to a difference in autonomic influence on ectopic activity, with a different balance between the sympathetic and parasympathetic systems between the 2 outflow tracts.
      The present case showed ectopic activity with atypical right bundle branch block–like morphology. When applying the classical morphological algorithms previously described, they all pointed to a left-sided SOO (Table 1). However, when the behavioral criteria were applied, a right-sided SOO was predicted. As shown in the Holter records in Figure 2, the morning hours showed greater VE activity compared to night time, accounting for high variability (CoV = 2.5), as well as several hours throughout the day having a VE burden less than 50, both being predictive of a right-sided SOO. In this example, subsequent mapping confirmed the accuracy of these 2 parameters. Conversely, the morphological criteria failed, likely owing to the marked clockwise rotation of the patient’s heart.
      Figure thumbnail gr2
      Figure 2Hourly trend summary of the number of ectopic beats on the 24-hour Holter monitor performed before the first (A) and the second (B) ablation procedures. Both summaries show hours with less than 50 ventricular ectopies (VE), as well as a high variability, with a CoV ≥0.7, suggesting a site of origin in the right ventricular outflow tract. AF = atrial fibrillation; VT = ventricular tachycardia.
      In relation to the recurrence of the arrhythmia after the first ablation, it could be owing to the fact that in the first procedure the site of greatest precocity, located above the PV, was ablated after the first set of lesions at the earliest site in the high RVOT and without the catheter in reverse U shape above the PV. A pronounced edematous response to the initial lesions may have led to failure to deliver enough energy to the true SOO. In the second attempt, the first lesion was delivered above the PV, where the earliest activation site was located, coinciding with the findings of the previous procedure. However, this time the catheter was placed directly as an inverted U within the pulmonary cusp, which probably facilitated delivering more effective initial applications. In both procedures, the VE had an identical morphology and the preprocedure 24-hour Holter showed high hourly variability, pointing to a right-sided SOO.
      This case illustrates the usefulness and reproducibility of the new behavior-based criteria, which are easily applicable to routine clinical practice.

      References

        • Park K.M.
        • Kim Y.H.
        • Marchlinski F.E.
        Using the surface electrocardiogram to localize the origin of idiopathic ventricular tachycardia.
        Pacing Clin Electrophysiol. 2012; 35: 1516-1527
        • Yoshida N.
        • Inden Y.
        • Uchikawa T.
        • et al.
        Novel transitional zone index allows more accurate differentiation between idiopathic right ventricular outflow tract and aortic sinus cusp ventricular arrhythmias.
        Heart Rhythm. 2011; 8: 349-356
        • Waight M.C.
        • Li A.C.
        • Leung L.W.
        • et al.
        Hourly variability in outflow tract ectopy as a predictor of its site of origin.
        J Cardiovasc Electrophysiol. 2022; 33: 7-16
        • Ouyang F.
        • Fotuhi P.
        • Ho S.Y.
        • et al.
        Repetitive monomorphic ventricular tachycardia originating from the aortic sinus cusp: electrocardiographic characterization for guiding catheter ablation.
        J Am Coll Cardiol. 2002; 39: 500-508
        • Yoshida N.
        • Yamada T.
        • McElderry H.T.
        • et al.
        A novel electrocardiographic criterion for differentiating a left from right ventricular outflow tract tachycardia origin: the V2s/V3R index.
        J Cardiovasc Electrophysiol. 2014; 25: 747-753
        • Betensky B.P.
        • Park R.E.
        • Marchlinski F.E.
        • et al.
        The V2 transition ratio: a new electrocardiographic criterion for distinguishing left from right ventricular outflow tract tachycardia origin.
        J Am Coll Cardiol. 2011; 57: 2255-2262
        • Kaypakli O.
        • Koca H.
        • Sahin D.Y.
        • Karataş F.
        • Ozbicer S.
        • Koç M.
        S-R difference in V1-V2 is a novel criterion for differentiating the left from right ventricular outflow tract arrhythmias.
        Ann Noninvasive Electrocardiol. 2018; 23: 1-5
        • Anter E.
        • Frankel D.S.
        • Marchlinski F.E.
        • Dixit S.
        Effect of electrocardiographic lead placement on localization of outflow tract tachycardias.
        Heart Rhythm. 2012; 9: 697-703
        • Tahara Y.
        • Mizuno H.
        • Ono A.
        • Ishikawa K.
        Evaluation of the electrocardiographic transitional zone by cardiac computed tomography.
        J Electrocardiol. 1991; 24: 239-245