Improved patient selection for cardiac resynchronization therapy by normalization of QRS duration to left ventricular dimension.

AIMS: This study evaluates the relative importance of two components of QRS prolongation, myocardial conduction velocity and travel distance of the electrical wave front (i.e. path length), for the prediction of acute response to cardiac resynchronization therapy (CRT) in left bundle branch block (LBBB) patients. METHODS AND RESULTS: Thirty-two CRT candidates (ejection fraction <35%, LBBB) underwent cardiac magnetic resonance (CMR) imaging to provide detailed information on left ventricular (LV) dimensions. Left ventricular end-diastolic volume (LVEDV) was used as a primary measure for path length, subsequently QRSd was normalized to LV dimension (i.e. QRSd divided by LVEDV) to adjust for conduction path length. Invasive pressure-volume loop analysis at baseline and during CRT was used to assess acute pump function improvement, expressed as LV stroke work (SW) change. During CRT, SW improved by +38 ± 46% (P < 0.001). The baseline LVEDV was positively related to QRSd (R = 0.36, P = 0.044). Despite this association, a paradoxical inverse relation was found between LVEDV and SW improvement during CRT (R = -0.40; P = 0.025). Baseline unadjusted QRSd was found to be unrelated to SW changes during CRT (R = 0.16; P = 0.383), whereas normalized QRSd (QRSd/LVEDV) yielded a strong correlation with CRT response (R = 0.49; P = 0.005). Other measures of LV dimension, including LV length, LV diameter, and LV end-systolic volume, showed similar relations with normalized QRSd and SW improvement. CONCLUSION: Since normalized QRSd reflects myocardial conduction properties, these findings suggest that myocardial conduction velocity rather than increased path length mainly determines response to CRT. Normalizing QRSd to LV dimension might provide a relatively simple method to improve patient selection for CRT.

The influence of right ventricular stimulation on acute response to cardiac resynchronisation therapy.

BACKGROUND: The contribution of right ventricular (RV) stimulation to cardiac resynchronisation therapy (CRT) remains controversial. RV stimulation might be associated with adverse haemodynamic effects, dependent on intrinsic right bundle branch conduction, presence of scar, RV function and other factors which may partly explain non-response to CRT. This study investigates to what degree RV stimulation modulates response to biventricular (BiV) stimulation in CRT candidates and which baseline factors, assessed by cardiac magnetic resonance imaging, determine this modulation. METHODS AND RESULTS: Forty-one patients (24 (59 %) males, 67 ± 10 years, QRS 153 ± 22 ms, 21 (51 %) ischaemic cardiomyopathy, left ventricular (LV) ejection fraction 25 ± 7 %), who successfully underwent temporary stimulation with pacing leads in the RV apex (RVapex) and left ventricular posterolateral (PL) wall were included. Stroke work, assessed by a conductance catheter, was used to assess acute haemodynamic response during baseline conditions and RVapex, PL (LV) and PL+RVapex (BiV) stimulation. Compared with baseline, stroke work improved similarly during LV and BiV stimulation (∆+ 51 ± 42 % and ∆+ 48 ± 47 %, both p < 0.001), but individual response showed substantial differences between LV and BiV stimulation. Multivariate analysis revealed that RV ejection fraction (ß = 1.01, p = 0.02) was an independent predictor for stroke work response during LV stimulation, but not for BiV stimulation. Other parameters, including atrioventricular delay and scar presence and localisation, did not predict stroke work response in CRT. CONCLUSION: The haemodynamic effect of addition of RVapex stimulation to LV stimulation differs widely among patients receiving CRT. Poor RV function is associated with poor response to LV but not BiV stimulation.

Magnetic resonance imaging, pacemakers and implantable cardioverter-defibrillators: current situation and clinical perspective.

New developments and expanding indications have resulted in a significant increase in the number of patients with pacemakers and internal cardioverterdefibrillators (ICDs). Because of its unique capabilities, magnetic resonance imaging (MRI) has become one of the most important imaging modalities for evaluation of the central nervous system, tumours, musculoskeletal disorders and some cardiovascular diseases. As a consequence of these developments, an increasing number of patients with implanted devices meet the standard indications for MRI examination. Due to the presence of potential life-threatening risks and interactions, however, pacemakers and ICDs are currently not approved by the Food and Drug Administration (FDA) for use in an MRI scanner. Despite these limitations and restrictions, a limited but still growing number of studies reporting on the effects and safety issues of MRI and implanted devices have been published. Because physicians will be increasingly confronted with the issue of MRI in patients with implanted devices, this overview is given. The effects of MRI on an implanted pacemaker and/or ICDs and vice versa are described and, based on the current literature, a strategy for safe performance of MRI in these patients is proposed. (Neth Heart J 2010;18:31-7.).