Premature ventricular contractions are a common type of arrhythmia and generally have a good prognosis. However, in some cases, conversion to ventricular tachycardia or cardiac dysfunction may occur secondary to premature ventricular contractions. In such cases, catheter ablation therapy is considered a suitable treatment option and may be used as a curative therapy.
In children, the right ventricular outflow tract is the most frequent origin of ventricular arrhythmias, followed by the tricuspid valve ring and aortic coronary cusps. However, in recent years, ventricular arrhythmias of epicardial origin, such as the left ventricle summit and crux, have also been reported. The crux is located in the posterior septum of the heart, bordering the four chambers. Ventricular arrhythmias originating from the crux can be energised from the coronary venous system. Conversely, the posterior–superior process of the left ventricle is anatomically defined as “the most inferior and posterior aspect of the basal left ventricle, posterior to the plane of the tricuspid valve.” The posterior–superior process of the left ventricle is in close proximity to the crux. Ventricular arrhythmias that originate from this area are ablated from the right atrium, left ventricle endocardium, and coronary venous system. Reference Cronin, Bogun and Maury1
In older patients, ventricular arrhythmias originating from the posterior–superior process of the left ventricle are more common and have a relatively high recurrence rate. However, such cases have not been reported in children. In this report, successful ablation of premature ventricular contractions originating from the posterior–superior process of the left ventricle via the right atrium approach in a paediatric patient is presented.
Case report
This is a case of an otherwise healthy, asymptomatic 13-year-old male weighing 57 kg who was referred to our hospital due to frequent premature ventricular contractions detected during a junior high school cardiac examination. A 12-lead electrocardiogram showed premature ventricular contractions in bigeminy. The premature ventricular contraction QRS waveform was a left superior axis with a left bundle branch block, a precordial transition in lead V2, and a polymorphic QRS waveform in V1. The maximum deflection index was 0.56 (Fig. 1). A premature ventricular contraction burden of 49% and three consecutive beats was shown in the Holter monitoring. The serum blood B-type natriuretic peptide level was elevated at 228 pg/mL. No cardiac structural abnormalities were shown during ultrasonography. It’s hard to evaluate cardiac size and function because of frequent premature ventricular contractions. Thus, ablation therapy for the frequent premature ventricular contractions was performed 3 months after diagnosis.
Figure 1. The patient’s 12-lead electrocardiogram. Premature ventricular contractions show left bundle branch configuration with left-axis deviation. Arrowheads indicate polymorphic QRS waveform in V1. The setting was 5.00 mm/mV, 25.0 mm/s.
The earliest ventricular activation site of the premature ventricular contractions was mapped from the femoral vein and retrogradely from the aorta using a three-dimensional electro-anatomical navigation system (CARTO3, BW), under general anaesthesia. A decapolar catheter (DECANAV 7F, Biosense Webster, CA, USA), a non-irrigated ablation catheter (NAVISTAR 7F B curve, BW), and an intracardiac ultrasound catheter (SOUNDSTAR 8F, BW) were used.
Delivery of radiofrequency energy to the right ventricle just below the tricuspid valve and to the endocardium of the basal left ventricle was rendered ineffective, while deliveries to the inferior region of the right atrium showed a transient effect. Coronary sinus venography was performed; however, in the vicinity of the site of the transient effect, no accessible vessels were found. The radiofrequency energy application (30 W, 55°C) to the inferior wall of the right atrium, 12.6 mm anterior to the coronary sinus ostium, eliminated ventricular arrhythmias without junctional rhythm or atrioventricular block (Fig. 2a–f). The intracardiac potential at this site showed the earliest rapid bipolar deflection compared to other sites, which was 18 ms earlier than in the surface electrocardiogram, although it did not show the maximum unipolar −dV/dT (Fig. 2g). The intracardiac ultrasound images identified the origin of the ventricular arrhythmias as posterior–superior process of the left ventricle (Fig. 2h). During the 1-year follow-up period, the patient had no recurrence and the serum blood B-type natriuretic peptide level was normalised. A MRI was not performed because the clinical course was not suggestive of cardiomyopathy.
Figure 2. a – f The CARTO UNIVU image integrated with right ventriculogram (a, b), left ventriculogram (c, d), coronary venogram (e, h) is present, with a right anterior oblique 30° and left anterior oblique 60° projection. Dots show the anatomic index and the ablated site. Yellow dot indicates his bundle, and green dots indicate tricuspid annulus, light green indicates coronary sinus ostium. The remaining tags are ablation sites. Light blue dots indicate the right ventricle below the tricuspid valve, and purple dots indicate the left ventricular endocardium; however, the energy delivery to these sites was ineffective. Orange dots reflect transient effect sites, and red dot indicates a successful site at the right atrium. g . The body surface electrogram (II and V5) and intracardiac electrogram (ABL). The successful site shows the earliest rapid bipolar (ABL bi) deflection, although it does not demonstrate a maximum unipolar–dV/dt (ABL uni). h . An intracardiac ultrasound image. A successful site is indicated by a red dot and is consistent with the so-called “posterior–superior process of the LV” anatomic site. ABL = ablation; RA = right atrium; LV = left ventricle; ao = aorta.
Discussion
This is the first report of a successful ablation of a paediatric case of premature ventricular contraction originating from the posterior–superior process of the left ventricle. The basal inferoseptal aspect of the left ventricle, the posterior–superior process of the left ventricle, will be in close proximity to the right atrium because the plane of the tricuspid annulus is slightly more apically deviated than the plane of the mitral annulus. Santangeli et al. reported five adult cases of premature ventricular contractions of posterior–superior process of the left ventricle origin that were treated by energising the right atrium. In these cases, despite mapping and ablation of the left ventricle and coronary venous system, the premature ventricular contractions persisted and were eventually successfully treated by energising from the right atrium. Reference Santangeli, Hutchinson and Supple2
A typical body surface electrocardiogram in ventricular arrhythmias of posterior–superior process of the left ventricle origin shows a right bundle branch block concordant pattern or an left bundle branch block pattern with an early transition by lead V2, a monophasic R wave in lead I, and an R wave amplitude in lead II greater than that in lead III. Reference Santangeli, Hutchinson and Supple2 Ventricular arrhythmias showing a left superior axis on the 12-lead electrocardiogram should be considered as a posterior–superior process of the left ventricle origin, and the result of this case was consistent. Reference Larsen, Shepard and Koneru3
Ventricular arrhythmias originating from the posterior–superior process of the left ventricle may arise intramurally. Recently, intramural ventricular arrhythmia characteristics such as multiple breakout sites and low amplitude potential have been reported. Higuchi et al. reported that maximal unipolar −dV/dT late from QRS at the site of successful ablation is a characteristic of intramural ventricular arrhythmias. Reference Higuchi, Yavin and Sroubek4 The 12-lead electrocardiogram polymorphism and the maximal unipolar −dV/dT delayed from the QRS suggested that this case was also an intramural premature ventricular contraction.
The atrioventricular nodal artery and septal artery are in close proximity to the posterior–superior process of the left ventricle region. Therefore, during the ablation procedure, an atrioventricular block must be monitored, and atrial pacing may be useful for monitoring the atrial-His interval to prevent it. Reference Masunaga, Matsunaga-Lee, Matsumoto, Tachibana and Takano5
In children, premature ventricular contractions exhibiting an left bundle branch block configuration with left-axis deviation may have a posterior–superior process of the left ventricle origin and can be successfully treated by delivering energy to the right atrium.
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