Mechanisms whereby rapid RV pacing causes LV dysfunction: perfusion-contraction matching and NO

• Published in: American journal of physiology. Heart and circulatory physiology Vol. 281; no. 6; pp. H2270 - H2281
• Main Authors: Nikolaidis, Lazaros A, Hentosz, Teresa, Doverspike, Aaron, Huerbin, Rhonda, Stolarski, Carol, Shen, You-Tang, Shannon, Richard P
• Format: Journal Article
• Language: English
• Published: United States 01.12.2001
• Subjects: Animals; Cell Respiration - physiology; Consciousness; Coronary Circulation - physiology; Dogs; Enzyme Inhibitors - pharmacology; Female; Glycogen - metabolism; Lactic Acid - metabolism; Male; Myocardial Contraction - physiology; Myocardial Stunning - metabolism; Myocardial Stunning - physiopathology; Myocardium - metabolism; Nitric Oxide - biosynthesis; Nitric Oxide - metabolism; Nitric Oxide Synthase - antagonists & inhibitors; Nitric Oxide Synthase - metabolism; Nitric Oxide Synthase Type III; Nitroarginine - pharmacology; Pacemaker, Artificial; Tachycardia - metabolism; Tachycardia - physiopathology; Ventricular Dysfunction, Left - metabolism; Ventricular Dysfunction, Left - physiopathology
• ISSN: 0363-6135; 1522-1539
• DOI: 10.1152/ajpheart.2001.281.6.h2270

1  Department of Medicine, Allegheny General Hospital, MCP-Hahnemann University School of Medicine, Pittsburgh 15212; and 2  Merck Research Laboratories, West Point, Pennsylvania 19486 Incessant tachycardia induces dilated cardiomyopathy in humans and experimental models; mechanisms are incompletely understood. We hypothesized that excessive chronotropic demands require compensatory contractility reductions to balance metabolic requirements. We studied 24 conscious dogs during rapid right ventricular (RV) pacing over 4 wk. We measured hemodynamic, coronary blood flow (CBF), myocardial O 2 consumption (M O 2 ) responses, myocardial nitric oxide (NO) production, and substrate utilization. Early pacing (6 h) resulted in decreased heart rate (HR)-adjusted coronary blood flow (CBF), M O 2 (CBF/beat: 0.33 ± 0.02 to 0.19 ± 0.01   ml, P  < 0.001, M O 2 /beat: 0.031 ± 0.002 to 0.016 ± 0.001 ml O 2 , P  < 0.001), and contractility [left ventricular (LV) first derivative pressure (dP/d t )/LV end-diastolic diameter (EDD): 65 ± 4 to 44   ± 3 mmHg · s 1 · mm 1 , P  < 0.01], consistent with flow-metabolism-function coupling, which persisted over the first 72 h of pacing (CBF/beat: 0.15   ± 0.01 ml, M O 2 /beat: 0.013 ± 0.001 ml O 2 , P  < 0.001). Thereafter, CBF per beat and M O 2 per beat increased (CBF/beat: 0.25 ± 0.01   ml, M O 2 /beat: 0.021 ± 0.001 ml O 2 at 28 days, P  < 0.01 vs. 72   h). Contractility declined [(LV dP/d t )/LVEDD: 19 ± 2 mmHg · s 1 · mm 1 , P  < 0.0001], signifying flow-function mismatch. Cardiac NO production, endothelial NO synthase expression, and fatty acid utilization decreased in late phase, whereas glycogen content and lactate uptake increased. Incessant tachycardia induces contractile, metabolic, and flow abnormalities reflecting flow-function matching early, but progresses to LV dysfunction late, despite restoration of flow and metabolism. The shift to flow-function mismatch is associated with impaired myocardial NO production. nitric oxide; cardiomyopathy; stunning; hibernation; myocardial metabolism