Optimization of Ventricular Function by Improving the Activation Sequence During Ventricular Pacing

Abstract

Abnormal electrical activation occurring during ventricular pacing reduces left ventricular (LV) pump function. Two strategies were compared to optimize LV function using ventricular pacing, minimal asynchrony and optimal sequence of electrical activation. ECG and hemodynamics aortic flowprobe, thermodilution cardiac output, LV pressure and its maximal rates of rise (LVdP/dtpos) and fall (LVdP/dtneg) were measured in anesthetized open-chest dogs (n = 7) with healthy hearts. The QRS duration (a measure of asynchrony of activation) was 47 +/- 5 ms during sinus rhythm and increased to 110 +/- 12 ms during DDD pacing at the right ventricular (RV) apex with a short AV interval. During pacing at the LV apex and LV base, the QRS duration was 8% +/- 7% and 15% +/- 7% (P < 0.05) longer than during RV apex pacing, respectively. Stroke volumes, LVdP/dtpos and LVdP/dtneg, however, were higher during LV apex (15% +/- 16%, 10% +/- 12% [P < 0.05], and 15% +/- 10%, respectively) and LV base pacing (11% +/- 12% [P < 0.05], 3% +/- 12%, and 3% +/- 11%, respectively) than during RV apex pacing. Systolic LV pressure was not influenced significantly by the site of pacing. Biventricular pacing (RV apex together with one or two LV sites) decreased the QRS duration by approximately 20% as compared with RV apex pacing, however, it did not improve stroke volumes, LVdP/dtpos and LVdP/dtneg beyond those during pacing at the LV apex alone. In conclusion, the sequence of electrical activation is a stronger determinant of ventricular function than the synchrony of activation. For optimal LV function the selection of an optimal single pacing site, like the LV apex, is more important than pacing from multiple sites.

Predictors of Systolic Augmentation From Left Ventricular Preexcitation in Patients With Dilated Cardiomyopathy and Intraventricular Conduction Delay

“…This dysfunction can be offset by concomitant stimulation of the opposing wall to restore synchrony, and improvement depends on the extent of dyssynchrony generated by the first lead. 17,18 Such observations have suggested that patients with DCM and basal discoordination might benefit from LV or biventricular VDD pacing, and this was recently confirmed. [2][3][4][5] However, the response magnitude varies, highlighting the importance of identifying responsive individuals.…”

“…Adding an LV free-wall pacemaker (ie, biventricular pacing) improves function, as reported experimentally. 17 We speculate that the major difference in this regard between DCM and normal hearts is that any improvement with recoordination becomes more significant in the former as other functional mechanisms fail.…”

“…However, analogous data have been reported in animal studies, and these consistently demonstrate that single-site (LV or RV) pacing of a heart with normal conduction (narrow QRS) produces a significant decline in dP/dt max and other markers of systolic function. 14,15,17,18,27 We also limited our analysis to DCM patients with widened QRS complexes, and it remains possible that some individuals with more narrow complexes might also benefit. Previous studies have reported regional wall motion abnormalities, heterogeneous wall stress, and myocardial perfusion in DCM patients with normal-appearing epicardial vessels, 28,29 although none reported QRS durations to test correlations with these phenomena.…”

Midterm Benefits of Left Univentricular Pacing in Patients With Congestive Heart Failure

“…Although there is no definite answer to this question, the most likely hypothesis, according to recent experimental and clinical data, 13,14,18,25 is that in patients with LBBB or in animals with experimentally induced LBBB, the LV contractions are totally desynchronized. [25][26][27][28][29] Schematically, the septal area is "akinetic" while the lateral wall is contracting normally but with a marked delay after other areas.…”

“…13,14 Nevertheless, although clinical improvement during permanent BIV pacing has been assessed in randomized 4,5 or prospective observational series, 15 very few results are available on permanent UNI LV pacing. Furthermore, these results were based on a limited number of patients 16 or included a very short-term follow-up.…”