The relation between the pacing sites in the right ventricular outflow tract and QRS morphology in the 12-lead ECG

[History of development of ventricular arrhythmias diagnostics]

This review shows historical steps in the development of topical diagnostics for ventricular arrhythmias, the current status of this issue, and the relevance of developing topical, noninvasive electrophysiological cardiac mapping.

Surface ECG and Fluoroscopy are Not Predictive of Right Ventricular Septal Lead Position Compared to Cardiac CT

BACKGROUND

Controversy exists regarding the optimal lead position for chronic right ventricular (RV) pacing. Placing a lead at the RV septum relies upon fluoroscopy assisted by a surface 12-lead electrocardiogram (ECG). We compared the postimplant lead position determined by ECG-gated multidetector contrast-enhanced computed tomography (MDCT) with the position derived from the surface 12-lead ECG.

METHODS

Eighteen patients with permanent RV leads were prospectively enrolled. Leads were placed in the RV septum (RVS) in 10 and the RV apex (RVA) in eight using fluoroscopy with anteroposterior and left anterior oblique 30° views. All patients underwent MDCT imaging and paced ECG analysis. ECG criteria were: QRS duration; QRS axis; positive or negative net QRS amplitude in leads I, aVL, V1, and V6; presence of notching in the inferior leads; and transition point in precordial leads at or after V4.

RESULTS

Of the 10 leads implanted in the RVS, computed tomography (CT) imaging revealed seven to be at the anterior RV wall, two at the anteroseptal junction, and one in the true septum. For the eight RVA leads, four were anterior, two septal, and two anteroseptal. All leads implanted in the RVS met at least one ECG criteria (median 3, range 1-6). However, no criteria were specific for septal position as judged by MDCT. Mean QRS duration was 160 ± 24 ms in the RVS group compared with 168 ± 14 ms for RVA pacing (P = 0.38).

CONCLUSIONS

We conclude that the surface ECG is not sufficiently accurate to determine RV septal lead tip position compared to cardiac CT.

Radiofrequency catheter ablation of idiopathic right ventricular outflow tract arrhythmias

Idiopathic ventricular arrhythmias (VA) consist of various subtypes of VA that occur in the absence of clinically apparent structural heart disease. Affected patients account for approximately 10% of all patients referred for evaluation of ventricular tachycardia (VT). Arrhythmias arising from the outflow tract (OT) are the most common subtype of idiopathic VA and more than 70-80% of idiopathic VTs or premature ventricular contractions (PVCs) originate from the right ventricular (RV) OT. Idiopathic OT arrhythmias are thought to be caused by adenosine-sensitive, cyclic adenosine monophosphate (cAMP) mediated triggered activity and, in general, manifest at a relatively early age. Usually they present as salvos of paroxysmal ventricular ectopic beats and are rarely life-threatening. When highly symptomatic and refractory to antiarrhythmic therapy or causative for ventricular dysfunction, ablation is a recommended treatment with a high success rate and a low risk of complications.

Real-time three-dimensional echocardiographic determination of right ventricular outflow tract high septal pacing sites

OBJECTIVE

To investigate the feasibility of determination of right ventricular outflow tract (RVOT) high septal pacing site visualized by real-time three-dimensional echocardiography (RT3DE).

METHODS

The forty subjects with RVOT pacing were analysed. RT3DE determination of RVOT high septal pacing sites was compared with chest X-ray (CXR).

RESULTS

RVOT septal pacing sites could be obtained in all patients by RT3DE.When pacing sites were categorized as septal or non-septal, there were good agreements between echocardiography and CXR (kappa = 0.745). However, when RVOT pacing sites were categorized as high septal or non-high septal in identifying the exact anatomic location of pacing sites, there was only mild agreement between echocardiography and CXR (kappa = 0.275). Moreover, when RT3DE was used as the gold standard in identifying the exact anatomic location of RVOT, pacing at the RVOT high septal could only be achieved in 37.5% (n= 15) of patients using RT3DE, but in 65% (n= 26) using CXR, because the RVOT septal pacing lead tip found at high septal by CXR is actually found at low septal or free wall by RT3DE.

CONCLUSION

It is limited to accurately locate RVOT high septal pacing site only by CXR, RT3DE allows to determinate the RVOT high septal pacing sites helpfully.

Ablation of Idiopathic Right Ventricular Outflow Tract Tachycardia: Current Perspectives

Ventricular tachycardia (VT) arising from the right ventricular outflow tract (RVOT) in the absence of overt structural heart disease is a common entity. Exclusion of occult structural disease such as arrhythmogenic right ventricular cardiomyopathy is critical as this diagnosis impacts both ablation outcomes and long-term prognosis. VT is most commonly due to triggered activity. Induction of the target arrhythmia in the laboratory is often problematic, and is frequently facilitated by catecholamine infusion. Recent data indicate that high-density three-dimensional activation mapping facilitates identification of target sites for ablation, and that the spatial resolution of pacemapping may be more limited than previously recognized. A standard 12-lead electrocardiogram is useful in providing an initial approximation of the site of origin within the outflow tract, and may contain subtle clues to potentially confounding foci on the left ventricular endocardial or epicardial surface. When sufficient arrhythmia is present to permit mapping, successful ablation can be expected in 90-95% of patients, with a recurrence risk of approximately 5%. In experienced centers, major complications are <or=1% and outcomes should approach those obtained for the common forms of supraventricular tachycardia.

Prevalence and Electrocardiographic Characteristics of Idiopathic Ventricular Arrhythmia Originating in the Free Wall of the Right Ventricular Outflow Tract

BACKGROUND

The prevalence and ECG characteristics of idiopathic ventricular arrhythmia originating in the free wall of the right ventricular outflow tract (RVOT) require further clarification, which was the aim of the present study of 110 patients with idiopathic ventricular tachycardia (n=34) or premature ventricular contraction (n=76; OT-VT/PVC) who underwent successful catheter ablation at the RVOT.

METHODS AND RESULTS

Ten OT-VT/PVCs (9%) were ablated successfully at the free wall (FW-VT/PVC); the remaining 100 (91%) were ablated at the RVOT septum (Sep-VT/PVC). R wave amplitudes in the inferior leads were significantly smaller in FW-VT/PVC than in Sep-VT/PVC (p<0.01). An RR' pattern in the inferior leads was observed significantly more often in FW-VT/PVC than in Sep-VT/PVC (p<0.001). QS-wave amplitude in each of leads V(1) to V(3) was significantly deeper in FW-VT/PVC than in Sep-VT/PVC (p<0.001). ECG criteria requiring an RR' pattern in all inferior leads as well as an S-wave amplitude of at least 3.0 mV in lead V(2) differentiated FW-VT/PVC from Sep-VT/PVC with high sensitivity, specificity, and predictive accuracy.

CONCLUSIONS

Although FW-VT/PVC has a relatively low prevalence, it has several distinctive ECG characteristics and detailed ECG analysis can differentiate it from Sep-VT/PVC.