Pictorial Review of CRT Implantation

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Pictorial review of CRT implantation. CRT is cardiac resynchronization therapy, also known as biventricular pacing and heart failure device.
Left subclavian venogram is usually the first step during the implantation of most cardiac implantable electronic devices. Iodinated contrast is injected into a left forearm vein and the live fluoroscopy images captured for use as a roadmap during percutaneous subclavian vein puncture for the introduction of intracardiac leads of the device.
Patient position on the table is not changed after acquisition of the venogram so that roadmap can be used for fluoroscopy guided subclavian vein puncture. Extrathoracic ‘subclavian’ (axillary) vein puncture is very much facilitated by the venogram roadmap.
Intrathoracic puncture is discouraged because of the chance of ‘subclavian crush’ and long term damage to the pacing leads. Intrathoracic subclavian puncture has also a risk of pneumothorax as an occasional complication.
The venogram is also useful to exclude anomalies and occlusion of the venous system prior to puncture. In case the veins are not found to be suitable, procedure is switched to the opposite side.
Once the subclavian puncture has been obtained, the right ventricular pacing lead can be introduced and screwed into the desired location. Screw in to the interventricular septum is often preferred to an apical location.
A steerable decapolar electrophysiology catheter introduced through a sheath is useful in guiding the sheath to the coronary sinus. Decapolar catheter can be removed once the sheath has been threaded well over it into the coronary sinus and seated well.
Coronary sinus venogram can be obtained by injecting iodinated contrast into the coronary sinus through the sheath. Balloon occlusion of the proximal coronary sinus can improve the visualisation of the coronary venous tree.
A guidewire can be introduced slowly through the sheath in the coronary sinus and navigated to a good posterolateral vein visualised by the previous coronary sinus venogram.
The left ventricular lead of the CRT device can be threaded over the guidewire in the posterolateral vein. The peel away sheath can be split using the device provided in the kit once a stable lead position has been obtained and tested.
Atrial lead can be introduced and positioned in the right atrial appendage. Proximal ends of all the leads are connected to the appropriate ports of the CRT device.
Three leads are seen in the left subclavian vein. Tip of the atrial lead is seen in the lower right corner. Redundant lead loops and the CRT device are seen in the left upper corner.
Final picture after implantation of a CRT device showing both ventricular leads, atrial lead, and a part of the device in the upper left corner of the image.
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.
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 ms, septal to posterior wall delay of more than 160 ms or septal to lateral wall delay of more than 60 ms in TVI. 3D synchronization is with colour coding of early and late contracting segments - early as green and late as red.

[@mahbubmansur4306]

Very good presentations.

[@JohnsonFrancisMBBSMDDM]

Thank you!