title: Limitation of cardiac output by total isovolumic time during pharmacologic stress in patients with dilated cardiomyopathy: activation-mediated effects of left bundle branch block and coronary artery disease.
abstract: OBJECTIVE
  We sought to separate the effects of associated left bundle branch block (LBBB) and coronary artery disease (CAD) on peak cardiac output (CO) during dobutamine stress in patients with dilated cardiomyopathy (DCM).
  
  
  BACKGROUND
  The mechanisms limiting CO during stress in patients with DCM are unclear. Both LBBB and CAD may do so by prolonging the total isovolumic time (t-IVT).
  
  
  METHODS
  A total of 59 patients with DCM-34 with CAD (20 normal activation [NA], 14 LBBB) and 25 without CAD (15 NA, 10 LBBB)-were studied. The total IVT (s/min; calculated as: 60 - [total ejection time + total filling time] ) and CO were measured by Doppler echocardiography.
  
  
  RESULTS
  At rest, t-IVT was 8 s/min longer with LBBB (p < 0.001), was unaffected by CAD, and did not correlate with rest CO. During stress, CO correlated with t-IVT (r = -0.73, p < 0.001) in all four patient groups. In the absence of CAD, t-IVT became shortened (NA by 7 +/- 3 s/min; LBBB by 9 +/- 4 s/min) and correlated with a fall in the QRS duration (NA: r = 0.87; LBBB: r = 0.91), and CO increased with stress (NA by 4.7 +/- 2.7 l/min; LBBB by 4.0 +/- 2.3 l/min; all p < 0.001). With CAD, t-IVT did not shorten normally with stress. Instead, t-IVT was 5.6 s/min longer and CO was 3.3 l/min lower than in those without CAD (both p < 0.001), and t-IVT did not correlate with the QRS duration.
  
  
  CONCLUSIONS
  In patients with DCM, t-IVT during pharmacologic stress depends on changes in ventricular activation induced by LBBB or CAD and is, by itself, a major determinant of peak CO during stress.
authors.affiliation: Department of Echocardiography, The Royal Brompton Hospital and Imperial College of Science, Medicine and Technology, London, United Kingdom. a.duncan@ic.ac.uk
authors.forename: Alison M
authors.initials: AM
authors.lastname: Duncan
authors.forename: Darrel P
authors.initials: DP
authors.lastname: Francis
authors.forename: Michael Y
authors.initials: MY
authors.lastname: Henein
authors.forename: Derek G
authors.initials: DG
authors.lastname: Gibson
mesh_terms: D000368:Aged; D002037:Bundle-Branch Block / Q000150:complications / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D002302:Cardiac Output / Q000187:drug effects* / Q000502:physiology*; D002306:Cardiac Volume / Q000187:drug effects / Q000502:physiology; D002311:Cardiomyopathy, Dilated / Q000150:complications / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D002320:Cardiovascular Physiological Phenomena / Q000187:drug effects; D003324:Coronary Artery Disease / Q000150:complications / Q000503:physiopathology; D015150:Echocardiography, Doppler; D025401:Echocardiography, Stress / Q000379:methods*; D004562:Electrocardiography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D013997:Time Factors