Left ventricle pacing challenges in cardiac resynchronization therapy systems

Fig. 1. LV lead threshold management according to manufacturer Fig. 1 Legend: Panel A: LV automatic threshold test for Medtronic devices (Vector Express), displaying loss of capture with intrinsic RV conduction. The channels displayed are: EGM 1 = atrial channel; ECG = the “large” RV dipole (coil to can) with A-V markers; EGM 3 = the “LV cathode–RV coil” dedicated channel (the same used for the “EffectivCRT” algorithm) displaying the “QR” morphology during LV capture and the “RS” morphology as loss of capture occurs at the ninth beat of the test (RV sense). Panel B LV auto-threshold for Boston Scientific devices, with the ER dedicated channel showing the pacing artifact changes corresponding to the loss of capture (LOC) Panel C: LV auto-capture test for Biotronik devices, with RV back up pacing occurring at loss of capture during the 0.6 V step threshold search. The red arrow in the left side of the tracing indicates RV and LV synchronous pacing; the red arrow in the right side of the tracing indicates the sequential RV to LV during back up RV pacing, as loss of LV capture occurs. Panel D: the algorithm LV ACap Confirm (Abbot Medical devices), adopts the ER by comparing the polarization…

Fig. 2. Left ventricle capture confirmation by “EffectivCRT Diagnostic” algorithm Fig. 2 legend: dedicated unipolar LV EGM (LV cathode–RV coil EGM) during biventricular or LV pacing; until the third paced beat a “Qr” morphology indicate the effective LV capture; the fourth beat represent a kind of fusion and the further beats are represented by an “rS” morphology indicating the loss of LV capture. (with permission by Medtronic).LV = left ventricle; RV = right ventricle; Y = LV effective OK; N = loss of LV effective capture; AS = atrial sense; Ab = atrial blanking; VS = ventricular.