CRT implantation pearls

CRT implantation pearls

CRT implantation pearls: Screw in lead for LV pacing can be used only if the sheath can be taken deep down into the vein as it is not introduced over a guide wire. If after screwing in, the lead has a high impedance and the threshold is high, it is likely to be on the pericardial side of the vein. It may be unscrewed and another position sought. Screw tip is only 1 mm and may not produce significant bleeding on unscrewing from the pericardial side. Screwing to the myocardial side typically shows ST elevation on the lead tip electrogram due to the injury current. If threshold is not good, electronic configuration with pacing from proximal electrode or other combinations can be tried to improve efficacy. Issue with previous active fixation leads were that future removal or repositioning was not possible and they were also unipolar, preventing electronic configuration of pacing.

Unlike in conventional pacing where we want to minimise ventricular pacing, in CRT we want full biventricular pacing to occur.This may mean programming shorter AV delay to prevent intrinsic conduction. Inappropriately long AV delay can also cause a tendency for MR. E-A fusion can cause diastolic MR, which in turn can worsen heart failure. Unduly short AV delay causes A wave truncation, which can also be associated with MR. Intra-atrial conduction delay due to atrial fibrosis can increase AV delay. Atrial septal pacing is useful in reducing intra-atrial conduction delay. Biatrial pacing is another option to synchronise the atrium. Drug therapy to slow AV conduction and prevent fusion is also useful to improve biventricular pacing in CRT. Echo guided optimisation of AV delay is also possible (Ritter’s method).

During V-V delay optimisation, in some cases an LV offset causing pre-excitation of the LV may improve cardiac output. In interventricular dyssynchrony RV ejects at LV end diastole.

Intraventricular dyssynchrony is manifest as QRS onset to pulmonary ejection compared to aortic ejection of more than 40 milliseconds, septal to posterior wall delay of more than 160 milliseconds or septal to lateral wall delay of more than 60 milliseconds in TVI. 3D synchronization is with colour coding of early and late contracting segments – early as green and late as red.

Maximum tracking rate has to be increased as heart failure status improves. This is for consistent pacing at higher rates needed during more activities permitted by better effort tolerance.

Transient worsening of renal function may be seen after CRT implantation due to the long procedure time. This may also cause worsening of heart failure. The longer procedure time also enhances the chances for infection. Subclavian vein thrombosis is another potential problem due to the presence of three leads and a sluggish circulation due to heart failure.