A Hybrid Score to Predict the Origin of Outflow Tract Ventricular Arrhythmias in Patients with Intraventricular Conduction Disorders or Paced Rhythm

Outflow tract ventricular arrhythmia (OTVA) is the most common type of ventricular arrhythmia, and catheter ablation (CA) is the primary treatment option for patients experiencing symptoms. Accurately identifying the origin site of OTVA is essential for effective catheter ablation, minimizing procedural risks, and enhancing treatment success. As a result, various algorithms have been created to estimate the OTVA site of origin (SOO) using the surface 12-lead electrocardiogram (ECG). However, most studies that developed these algorithms or scoring systems for distinguishing OTVA origins excluded participants with structural heart disease and those with paced rhythms from their study groups. Consequently, the effectiveness and applicability of these algorithms in patients with intraventricular conduction defects or paced rhythms remain uncertain.

Additionally, some scores were formulated by contrasting certain OTVA characteristics with those of the basal QRS complex, which reduces their accuracy in individuals with intraventricular conduction issues and paced rhythms. Moreover, certain criteria are applicable only to OTVAs exhibiting a specific ECG pattern, and some demonstrate suboptimal inter-observer reliability in ECG measurements. To address these limitations, our research team conducted a prospective evaluation of a hybrid score (HS) that integrates both clinical and ECG data to predict OTVA-SOO, including patients with cardiac implantable electronic devices and those with structural heart disease in our study.

This study aimed to assess the effectiveness of the previously described hybrid algorithm in predicting OTVA-SOO in a patient population characterized by a wide basal QRS due to intraventricular conduction defects or paced rhythms.

The Hybrid Score The Hybrid Score (HS), detailed in previous literature 10, involves a sum of points based on clinical and ECG characteristics. Points are assigned as follows: one point each for being over 50 years old, male, and having arterial hypertension. ECG-based points are allocated according to QRS transition: 3 points for a transition in V1, 2 points for V2, 1 point for V3 if the R-wave in V3 is greater than 1 mV; 1 point is subtracted if V3 has an R-wave less than 1 mV, and further deductions or additions apply for transitions up to V6. A score ≤ 1 suggests an RVOT origin, whereas ≥ 2 suggests an LVOT origin.

ECGs were recorded with a standard configuration at a 25 mm/s sweep speed. Two independent electrophysiologists will perform blinded ECG analysis using digitized tracings and electronic calipers, maintaining a sweep speed of 100 mm/s and an amplification of 10 mm/mV. The precordial R/S transition was defined as the first precordial lead showing a dominant R wave. Additional score comparisons are documented in other studies.

Premature Ventricular Contraction (PVC) Ablation The CARTO3 three-dimensional navigation system (Biosense Webster, Johnson & Johnson Medical S.p.A., CA, USA) was utilized to guide all procedures. Mapping and ablation were performed using a contact force-sensing catheter with a 3.5 mm irrigated tip (ThermoCool SmartTouch, Biosense Webster). Activation mapping of spontaneous OTVAs was conducted. The procedure aimed to abolish spontaneous OTVAs, with the site of ablation marking the site of origin (SOO). OTVAs that originated from the left ventricular summit were categorized as LVOT-OTVAs, even if additional ablation from the distal coronary sinus was necessary to complete the procedure.

Collected data

• Patient Information and Consent (procedure must be done within 60 days of consent)
• Demographics (age, gender, etc.)
• Vital signs (length, weight, etc.)
• Medical history, including cardiovascular risk factors as hypertension, diabetes, dyslipidemia and smoking habit, heart disease, medication and antiarrhythmic drugs (AAD) at the moment of the procedure
• ECG data (ventricular extrasystoles morphology at 12-lead ECG and burden at 24 hours Holter ECG)
• Echocardiographic data (left ventricular ejection fraction and left ventricular end-diastolic diameter)
• Procedure data (number of radiofrequency applications, site of effective ablation, total radiofrequency time, total fluoro time, points mapping, procedure time)
• Adverse Events collected from the time the subject signs the informed consent onwards.