Left or biventricular (BiV) pacing, or cardiac resynchronization therapy, was proposed
nearly 10 years ago as an adjunctive treatment for patients with advanced heart failure
(HF) complicated by discoordinate contraction due to intraventricular conduction delay.
Since then, both short-term and a growing number of long-term clinical trials have
reported on the mechanisms and short- and mid-term efficacy of this approach, with
encouraging results. Therapy is implemented with novel pacing systems incorporating
an endocardial lead to stimulate the lateral free wall via a cardiac vein, and often
a right ventricular (RV) apex lead to provide BiV stimulation. A third atrial sensing
lead monitors intrinsic rhythm and provides timing data to ensure ventricular pre-excitation.
Modulation of the electronic atrial-ventricular (AV) time delay can optimize contractile
synchrony, enhance the contribution of atrial systole, and reduce mitral regurgitation.
Individuals with advanced HF, a wide QRS complex often with an AV time delay, and
evidence of contraction dyssynchrony in viable myocardium represent the target patient
group. Short-term studies reveal systolic augmentation and chamber efficiency from
pacing resynchronization that can be substantial. Long-term studies reveal improved
symptoms and exercise capacity, and some report reversal of chronic cardiac dilation.
However, important questions regarding long-term efficacy and mortality impact, optimal
mode for pacing stimulation, and role of combined pacing/cardioverter/defibrillation
devices remain unresolved. Here we review pathophysiologic mechanisms, short- and
long-term clinical results, and future directions of this new and promising therapy.