Diagnosis of atrial tachycardias originating from the lower right atrium: importance of P-wave morphology in the precordial leads V3–V6

AIMS: This study aimed to characterize P-wave morphology (PWM) in leads V3-V6 during focal atrial tachycardia (AT) originating from the lower right atrium (RA), and to investigate the role of interatrial conduction (IAC) pathways in the formation of PWM. METHODS AND RESULTS: Twenty-eight consecutive patients with tachycardia foci in the lower RA underwent detailed atrial endocardial activation mapping and radiofrequency catheter ablation. P-wave configuration was analysed using standard 12-lead electrocardiogram. Atrial tachycardia originated from lower non-septal tricuspid annulus (LTA) (n = 11), coronary sinus ostium (CSo) (n = 11), lower crista terminalis (LCT) (n = 4), or lower free wall (n = 2). In leads V3-V6, PWM showed a negative pattern in at least two consecutive leads during AT originating from CSo (11/11) and LTA (9/11), with an associated sensitivity of 91%, specificity of 100%, positive predictive value (PPV) of 100%, and negative predictive value (NPV) of 75%. A positive PWM was observed in three of four ATs originating from LCT, with an associated sensitivity of 75%, specificity of 100%, PPV of 60%, and NPV of 96%. A negative PWM in V3-V6 was consistent with a preferential IAC through musculature in the vicinity of the CS and an activation of both atria in an antero-posterior direction. In contrast, a positive PWM was associated with the engagement of a posterior (non-CS-related) interatrial connection. CONCLUSION: Characteristic PWMs in V3-V6 may accurately differentiate the anatomic sites of AT from the low RA with high PPVs and NPVs. P-wave morphology in V3-V6 is likely to be influenced by the engagement of the preferential IAC.