Document Detail

Cardiac Resynchronization Therapy Mediated Effects on Exercise Left Ventricular Function, Oxygen Uptake Kinetics, and Peak Oxygen Uptake in Heart Failure.
MedLine Citation:
PMID:  22523249     Owner:  NLM     Status:  Publisher    
To better understand the mechanisms contributing to improved exercise capacity with cardiac resynchronization therapy (CRT), we studied the effects of 6 mo of CRT on pulmonary oxygen uptake (VO(2)) kinetics, exercise left ventricular (LV) function, and peak VO(2) in 12 subjects (age: 56±15 yrs; peak VO(2): 12.9±3.2 ml/kg/min; ejection fraction: 18±3%) with heart failure. We hypothesized that CRT would speed VO2 kinetics due to an increase in stroke volume secondary to a reduction in LV end-systolic volume (ESV), and that the increase in peak VO(2) would be related to an increase in cardiac output reserve. We found that VO(2) kinetics were faster during the transition to moderate-intensity exercise following CRT (pre-CRT: 69±21 s vs post-CRT: 54±17 s; P<0.05). During moderate-intensity exercise, LV ESV reserve (exercise-resting) increased 9±7 ml (vs a 3±9 ml decrease pre-CRT; P<0.05), and steady-state stroke volume increased (pre-CRT: 42±8 ml vs post-CRT: 61±12 ml; P<0.05). LV end-diastolic volume did not change from rest to steady-state exercise post-CRT (P>0.05). CRT improved heart rate measured as a lower resting and steady-state exercise heart rate, and as faster heart rate kinetics following CRT (pre-CRT: 89±12 s vs post-CRT: 69±21 s; P<0.05). For peak exercise, cardiac output reserve increased significantly post-CRT, and was 22% higher at peak exercise post-CRT (both P<0.05). The increase in cardiac output was due to both a significant increase in peak and reserve stroke volume and to a non-significant increase in heart rate reserve. Similar patterns in LV volumes as moderate-intensity exercise were observed at peak exercise. Cardiac output reserve was related to peak VO(2) (r=0.48, P<0.05). These findings demonstrate the chronic CRT mediated cardiac factors that contribute, in part, to the speeding in phase II pulmonary VO(2) kinetics and increase in peak VO2 in clinically stable HF patients.
Corey R Tomczak; Ian Paterson; Mark J Haykowsky; Richard Lawrance; Andres Martellotto; Alfredo Pantano; Sajad Gulamhusein; Robert G Haennel
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-4-20
Journal Detail:
Title:  American journal of physiology. Heart and circulatory physiology     Volume:  -     ISSN:  1522-1539     ISO Abbreviation:  -     Publication Date:  2012 Apr 
Date Detail:
Created Date:  2012-4-23     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  100901228     Medline TA:  Am J Physiol Heart Circ Physiol     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
1University of Alberta.
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