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Cardiac Resynchronization Therapy

Practice Essentials

Cardiac resynchronization therapy (CRT), also known as biventricular pacing or multisite ventricular pacing, involves simultaneous pacing of the right ventricle (RV) and the left ventricle (LV). In addition to a conventional RV endocardial lead (with or without a right atrial [RA] lead), CRT involves an additional coronary sinus lead placed for LV pacing.


A pacemaker is an electronic device, approximately the size of a pocket watch, that senses intrinsic heart rhythms and provides electrical stimulation when indicated. Cardiac pacing can be either temporary or permanent.

Permanent pacing is most commonly accomplished through transvenous placement of leads to the endocardium (ie, RA or RV) or epicardium (ie, the LV surface via the coronary sinus [CS]), which are subsequently connected to a pacing generator placed subcutaneously in the infraclavicular region.

CRT is a specialized type of pacemaker therapy that provides biventricular pacing. This is carried out with or without the use of an implantable cardioverter-defibrillator (ICD), a device employed for treatment and prophylaxis in patients at risk for ventricular tachycardia (VT) or ventricular fibrillation (VF).

See Periprocedural Care for more detail.


Access to the CS for implantation of the LV lead may be achieved via the axillary, subclavian, or cephalic vein.

To facilitate stable LV lead placement, it is practical first to place the RV pacing lead and then to advance the LV lead into the CS branch, leaving the sheath in place. After the RA lead is positioned, the LV lead guiding sheath is removed, and the LV lead is sutured in place.

RV lead

In most cases, the delivery system sheath is passed over a guidewire into the RA and then advanced slowly into the RV, where 90°-180° of counterclockwise rotation is subsequently applied while the sheath is gently withdrawn and then advanced. This maneuver generally brings the sheath to the CS or the vicinity of the CS os, allowing easy cannulation of the CS with a guidewire.

LV lead

Although it may be possible to place the LV lead without knowing the anatomy of the CS and its branches, it is prudent to obtain a CS phlebogram to direct the selection and placement of this lead.

Successful resynchronization can be achieved with placement of the LV lead in almost any CS branch, provided that the site is in the proximal third to the middle third of the LV.

Several techniques have been described for branch cannulation, including the following:

Branches with acute-angle origins can often be cannulated with an angioplasty wire without any difficulty.

If a branch originating at a right or obtuse angle is difficult to cannulate, an inner catheter may be inserted near the preselected branch so that the guidewire can be advanced into the branch; once this is accomplished, the catheter may be exchanged for a packing lead while the wire position is maintained.

Alternatively, in such problematic cases, a larger-lumen inner catheter may be used to allow delivery of the pacing lead; this technique has been simplified by using a lead with an exaggerated curve, through which a stylet or angioplasty guidewire is advanced to direct the lead tip into the appropriate venous branch.

See Technique for more detail.

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