title: Ventricular activation sequence during left ventricular pacing promotes QRS complex oversensing in the atrial channel.
abstract: BACKGROUND
  Left ventricular (LV)-only pacing has a significant effect on delay in depolarization of parts of the ventricles that are likely oversensed in the right atrial channel. The study aimed to assess the impact of ventricular activation sequence on QRS oversensing and far-field endless-loop pacemaker tachycardia (ELT) in patients who received cardiac resynchronization therapy (CRT) devices.
  
  
  METHODS
  The study examined 102 patients with CRT devices. Oversensing artifacts in the atrial channel were inspected on intracardiac electrograms, and their timing with respect to the beginning of QRS was determined during DDD-right ventricular (RV), DDD-LV, DDD-biventricular (BiV), and AAI pacing modes. The occurrence of ELT during DDD-LV pacing with a postventricular atrial refractory period (PVARP) of 250 ms was also assessed.
  
  
  RESULTS
  The timing of oversensing artifacts (in relation to the beginning of surface QRS) was dependent on ventricular activation sequence, occurring promptly following intrinsic activation via the right bundle branch (47.1 ± 26.4 ms), later during RV pacing (108.7 ± 22.5 ms) or BiV pacing (109.4 ± 23.1 ms), and significantly later, corresponding to the final part of the QRS, during LV pacing (209.6 ± 40.0 ms, range: 140-340 ms, P < 0.001). Oversensing was significantly more frequent during LV than during RV pacing (35.3% vs 22.5%, P < 0.001). Far-field ELT was observed in six patients.
  
  
  CONCLUSIONS
  Oversensing artifacts in the atrial channel are likely caused by depolarization of the basal part of the right ventricle. The novel mechanism of QRS oversensing outside PVARP, caused by a reversed ventricular activation sequence during LV-only pacing, may be important in some CRT patients.
authors.affiliation: First Department of Cardiology and Hypertension, University Hospital, Cracow, Poland. mcjastrz@cyf-kr.edu.pl
authors.forename: Marek
authors.initials: M
authors.lastname: Jastrzebski
mesh_terms: D000368:Aged; D016477:Artifacts; D058406:Cardiac Resynchronization Therapy / Q000379:methods*; D058409:Cardiac Resynchronization Therapy Devices; D004562:Electrocardiography; D005260:Female; D006325:Heart Atria / Q000503:physiopathology; D006329:Heart Conduction System / Q000503:physiopathology; D006333:Heart Failure / Q000628:therapy*; D006352:Heart Ventricles / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D017202:Myocardial Ischemia / Q000628:therapy