12-lead ECG characteristics of PVCs/IVTs originating from the endocardial and epicardial mitral annulus.

Capital letters (Q,R,S) refer to relatively high-amplitude waves (>5 mm). Conversely, lowercase letters (q,r,s) refer to relatively low-amplitude waves(≤5 mm). MA: mitral annulus; Transition: the site of R-wave transition in the precordial leads; PdW: pseudo delta wave time; IDT: intrinsicoid deflection time; QRS: duration of the QRS complex; AL-EP MA: anterolateral portion of the epicardial MA; PL-EP MA: posterolateral portion of the epicardial MA; PS-EP MA: posteroseptal portion of the epicardial MA; PS-EN MA: posteroseptal portion of the endocardial MA; AL-EN MA: anterolateral portion of the endocardial MA; PL-EN MA: posterolateral portion of the endocardial MA; MS-EN MA: midseptal portion of the endocardial MA.