title: The problem of non-response to cardiac resynchronization therapy.
abstract: OBJECTIVE
  Cardiac resynchronization therapy improves quality of life, exercise performance, left ventricular ejection fraction, and reduces heart failure hospitalizations and mortality in patients with New York Heart Association class III or IV congestive heart failure and intraventricular conduction delay. A number of key clinical research questions remain, perhaps most importantly the issue of why apparently suitable patients do not respond to cardiac resynchronization therapy. These issues are also relevant to patients who do respond to cardiac resynchronization therapy as potentially their response might be further increased. This article will review the data regarding the frequency of the problem of non-response to cardiac resynchronization therapy and then discuss the postulated reasons and potential solutions.
  
  
  RESULTS
  Rates of non-response to cardiac resynchronization therapy are often quoted as 20-30%, but a critical analysis of the data would suggest the true non-responder rate can be estimated as perhaps 40-50%. The data indicate that on a population basis non-response is multi-factorial and the extent of mechanical dyssynchrony, left ventricular pacing site and cause of congestive heart failure are likely to be important. Ongoing research is exploring the utility of various techniques for quantifying mechanical dyssynchrony and the potential benefits of targeted left ventricular lead placement and post-implant optimization.
  
  
  CONCLUSIONS
  Cardiac resynchronization therapy is a major breakthrough in treatment for advanced congestive heart failure patients. There is substantial rate of non-response to this therapy, however, and research is exploring various ways to increase the response to the technique.
authors.affiliation: University of Ottawa Heart Institute, Ottawa, Ontario, Canada. dbirnie@ottawaheart.ca
authors.forename: David H
authors.initials: DH
authors.lastname: Birnie
authors.forename: Anthony Sl
authors.initials: AS
authors.lastname: Tang
mesh_terms: D002304:Cardiac Pacing, Artificial; D006329:Heart Conduction System / Q000503:physiopathology; D006333:Heart Failure / Q000503:physiopathology / Q000628:therapy*; D006801:Humans; D013318:Stroke Volume / Q000502:physiology; D017211:Treatment Failure