In the right place at the right (conduction) time

Approximately one-third of patients with cardiac resynchronization therapy (CRT) do not experience clinical benefit despite fulfilling the criteria for guideline-recommended device implant. To reduce the nonresponder rate and enhance the benefit of CRT in responders, robust research studies on CRT have concentrated on the optimal selection of CRT candidates and ideal sites of ventricular leads. Based on acute hemodynamic data from early CRT studies, the left ventricular (LV) lead position was guided by anatomical criteria with the lateral wall being the preferable location. However, there was little linkage between CRT outcomes and anatomically guided LV lead placement, aside from the observation that apical sites were associated with worse outcomes. 1 Singh J.P. Klein H.U. Huang D.T. et al. Left ventricular lead position and clinical outcome in the Multicenter Automatic Defibrillator Implantation Trial-Cardiac Resynchronization Therapy (MADIT-CRT) trial. Circulation. 2011; 123: 1159-1166 Crossref PubMed Scopus (455) Google Scholar Therefore, later studies shifted their focus to a more physiologic approach by targeting the area with delayed mechanical or electrical activation. Several advanced imaging modalities have been used to identify the delayed mechanical activation area. Although identifying the sites of late LV activation using speckle tracking echocardiography was linked to better CRT outcomes, 2 Khan F.Z. Virdee M.S. Palmer C.R. et al. Targeted left ventricular lead placement to guide cardiac resynchronization therapy: the TARGET study: a randomized, controlled trial. J Am Coll Cardiol. 2012; 59: 1509-1518 Crossref PubMed Scopus (531) Google Scholar ,3 Saba S. Marek J. Schwartzman D. et al. Echocardiography-guided left ventricular lead placement for cardiac resynchronization therapy: results of the Speckle Tracking Assisted Resynchronization Therapy for Electrode Region trial. Circ Heart Fail. 2013; 6: 427-434 Crossref PubMed Scopus (281) Google Scholar the difficulties in reliably performing speckle tracking and translating the area in the echocardiogram to its location in fluoroscopic views perioperatively is a barrier to adoption. Additionally, a randomized controlled trial using integrated cardiac imaging with radial strain echocardiography, cardiac computed tomography, and cardiac magnetic resonance imaging with gadolinium contrast to guide LV lead placement failed to significantly lower death or heart failure (HF) hospitalization. 4 Borgquist R. Carlsson M. Markstad H. et al. Cardiac resynchronization therapy guided by echocardiography, MRI, and CT imaging: a randomized controlled study. JACC Clin Electrophysiol. 2020; 6: 1300-1309 Crossref PubMed Scopus (19) Google Scholar Consequently, based on the principle of electromechanical coupling, 5 Singh J.P. Fan D. Heist E.K. et al. Left ventricular lead electrical delay predicts response to cardiac resynchronization therapy. Heart Rhythm. 2006; 3: 1285-1292 Abstract Full Text Full Text PDF PubMed Scopus (218) Google Scholar electrical indices of cardiac dyssynchrony have become more frequently used for guiding LV lead placement. Association of interventricular activation delay with clinical outcomes in cardiac resynchronization therapyHeart RhythmVol. 20Issue 3PreviewPacing at sites of longest interventricular delay has been associated with greater reverse remodeling in cardiac resynchronization therapy (CRT). However, the effects of pacing at such sites on clinical outcomes is less well studied. Full-Text PDF