[Effects of prolonged endocardial stimulation on left ventricular mechanical synchrony. A pilot study applying gated-SPECT phase analysis. Endocardial stimulation and dyssynchrony].

OBJETIVE: To evaluate left ventricular mechanical dyssynchrony (LVMD) associated with prolonged right ventricular pacing through an innovative imaging technique as a pilot study in Uruguay.

METHODS: A 99mTc-MIBI gated-SPECT and phase analysis was performed in 12 patients with pace-makers implanted at least one year before scintigraphy, due to advanced atrioventricular block. Clinical data, QRS duration, rate, mode and site of pacing in right ventricle, chamber diameters, presence and extension of myocardial scar and ischaemia, as well as LVEF at rest, were recorded. Using V-Sync of Emory Cardiac Toolbox, a standard deviation (PSD) and bandwidth (PBW) from rest phase histogram was obtained and these indexes were compared with controls in the subgroups of patients with LVEF≥50% and <50%.

RESULTS: Patients with prolonged RV endocardial pacing exhibited marked LVMD. More severe dyssynchrony was found in patients with impaired LVEF than in patients with preserved LVEF (PSD: 46.67o vs. 26.81o , P<.05; PBW: 144.33o vs. 77.41o , P<.05). Higher left ventricle diameters, extensive infarct, or significant ischaemia were found in patients with impaired LVEF.

CONCLUSIONS: Chronic right ventricular pacing was invariably associated with LVMD, even when systolic function was preserved. Phase analysis could be a potentially useful technique to evaluate LMVD associated with myocardial scar in patients with pacemakers, and to decide promptly the upgrading to biventricular pacing.