Biventricular Pacing

Biventricular pacing is an excellent option for certain patients with advanced HF. Also known as “cardiac resynchronization therapy,” biventricular pacing has been shown to improve HF symptoms in a majority of cases.

The normal cardiac conduction system delivers the electrical impulse to both the right and left ventricles simultaneously; however, in the presence of a left bundle branch block or right bundle branch block, the electrical impulse will reach one ventricle first then slowly transmit to the other causing “cardiac dyssynchrony.” Remember that a left bundle branch block and right bundle branch block, by definition, prolong the QRS duration.

A biventricular pacemaker is inserted in the same fashion as a standard pacemaker via the subclavian vein. The major distinguishing feature of a biventricular pacemaker is the insertion of a left ventricular lead to accomplish left ventricular pacing, in addition to the right ventricular lead for right ventricular pacing. The left ventricular lead is inserted through the coronary sinus in the right atrium, then fed posteriorly toward the left ventricle.

The indications for biventricular pacing are as follows:

1. Left ventricular ejection fraction < 35%, a QRS duration of > 120 ms and New York Heart Association (NYHA) functional class III or IV with optimal medical therapy.
2. Left ventricular ejection fraction < 35% and frequent reliance on right ventricular pacing (which significantly prolongs the QRS duration).
3. Left ventricular ejection fraction < 35% and NYHA functional class I or II who are undergoing pacemaker or implantable cardioverter defibrillator insertion and may rely on frequent cardiac pacing.

*Note: Meta-analysis has shown a mortality benefit for those patients with a QRS duration of > 150 ms who receive biventricular pacing and not those with a QRS duration < 150 ms.

*Note: Many patients who are candidates for biventricular pacing also receive an ICD at the same time.

When atrial fibrillation is present, the QRS complex occurs at random intervals and the biventricular pacing device does not know when to initiate atrial pacing and may not be able to initiate biventricular pacing (if the native QRS complex comes earlier than expected). This results in less beneficial effects on cardiac output, and thus symptoms.

Therefore, it is recommended that any patient with permanent atrial fibrillation undergoing biventricular pacing also have AV nodal ablation performed to eliminate the unpredictability of the onset of the QRS complex and allow for near 100% biventricular pacing.