Paced right ventricular rhythm: Different perfusion defects compared to left bundle branch block

Objectives Whether patients (pts) with paced right ventricular rhythm (PACED), mimicking left bundle branch block (LBBB), have similar patterns of perfusion abnormality to LBBB pts is unknown.

Methods Of 44,407 pts having rest/stress myocardial perfusion SPECT, we identified consecutive PACED and LBBB pts. Pts with known CAD, cardiomyopathy, an EF ≤ 40% or cardiac transplantation were excluded. In pts who had normal coronary angiography NCA (n=79) or who had a low likelihood of CAD (Llk) (n=129), quantitative perfusion defect scores using QPS software (17 segments; 0=normal, 4=most severe) were compared in PACED vs LBBB.

Results In PACED pts, abnormal summed stress score (SSS ≥4) was seen in 18/40 (45%) in the NCA group and in 25/66 (38%) in the Llk group. In LBBB pts, abnormal SSS was seen in 26/39 (67%) in the NCA group and in 17/63 (27%) in the Llk group. In PACED NCA pts, abnormal stress segmental perfusion scores (SPS ≥2) most commonly occurred in infero-apical (83%, SPS 1.9±0.9) and apical (89%, SPS 2.1±0.6) segments, whereas in LBBB NCA pts, defects were most common in the apical-septal (73%, SPS 1.8±0.8), apical-anterior (50%, SPS 1.2±0.9) and apical (62%, SPS 1.5±1.0) segments. In PACED NCA pts, reversible defects (SDS ≥1) were most common in the apex (44%, SDS 0.5±0.6), whereas in LBBB NCA pts, perfusion defects were most common in apical-anterior (54%, SDS 0.8±0.8) and apical-septal segments (58%, SDS 0.9±1.1). In Llk pts, locations of abnormal SPS and SDS in PACED and LBBB pts were similar to those of the respective NCA pts.

Conclusions In NCA and Llk pts with PACED rhythm or LBBB, myocardial perfusion defects are common, but have distinctly different patterns. Similar to LBBB, in 60% of PACED pts, perfusion defects are reversible