For the past 2 decades, catheter ablation stole most of the excitement in electrophysiology. Cardiac pacing was seen as necessary but boring. His-bundle pacing earned only modest attention.
But at the annual scientific sessions of the Heart Rhythm Society, cardiac pacing consolidated its comeback and entered the super-cool category.
Dr. John Mandrola
Not one but three late-breaking clinical trials considered the role of pacing the heart’s conduction system for both preventive and therapeutic purposes. Conduction system pacing, or CSP as we call it, includes pacing the His bundle or the left bundle branch. Left bundle–branch pacing has now largely replaced His-bundle pacing.
Before I tell you about the studies, let’s review why CSP disrupts the status quo.
The core idea goes back to basic physiology: After the impulse leaves the atrioventricular node, the heart’s specialized conduction system allows rapid and synchronous conduction to both the right and left ventricles.
Standard cardiac pacing means fixing a pacing lead into the muscle of the right ventricle. From that spot, conduction spreads via slower muscle-to-muscle conduction, which leads to a wide QRS complex and the right ventricle contracts before the left ventricle.
While such dyssynchronous contraction is better than no contraction, this approach leads to a pacing-induced cardiomyopathy in a substantial number of cases. (The incidence reported in many studies varies widely.)
The most disruptive effect of conduction system pacing is that it is a form of cardiac resynchronization therapy (CRT). And that is nifty because, until recently, resynchronizing the ventricles required placing two ventricular leads: one in the right ventricle and the other in the coronary sinus to pace the left ventricle.
Left bundle-branch pacing vs. biventricular pacing
The first of the three HRS studies is the LBBP-RESYNC randomized controlled trial led by Jiangang Zou, MD, PhD, and performed in multiple centers in China. It compared the efficacy of left bundle–branch pacing (LBBP) with that of conventional biventricular pacing in 40 patients with heart failure who were eligible for CRT. The primary endpoint was the change in left ventricular ejection fraction (LVEF) from baseline to 6-month follow-up.
[embed:render:related:node:254502]
The results favored LBBP. Although both pacing techniques improved LVEF from baseline, the between-group difference in LVEF was greater in the LBBP arm than the biventricular pacing arm by a statistically significant 5.6% (95% confidence interval, 0.3%-10.9%). Secondary endpoints, such as reductions in left ventricular end-systolic volume, N-terminal of the prohormone brain natriuretic peptide, and QRS duration, also favored LBBP.
Conduction system pacing vs. biventricular pacing
A second late-breaking study, from the Geisinger group, led by Pugazhendhi Vijayaraman, MD, was simultaneously published in Heart Rhythm.
This nonrandomized observational study compared nearly 500 patients eligible for CRT treated at two health systems. One group favors conduction system pacing and the other does traditional biventricular pacing, which set up a two-armed comparison.
CSP was accomplished by LBBP (65%) and His-bundle pacing (35%).
The primary endpoint of death or first hospitalization for heart failure occurred in 28.3% of patients in the CSP arm versus 38.4% of the biventricular arm (hazard ratio, 1.52; 95% CI, 1.08-2.09). QRS duration and LVEF also improved from baseline in both groups.