Myocardial high-energy phosphate metabolism in patients with stable chronic dilated cardiomyopathy under a dobutamine-induced prolonged mild workload.
BACKGROUND
The myocardial phosphocreatine (PCr) to beta-adenosine triphosphate ratio measured by phosphorus 31 nuclear magnetic resonance spectroscopy, which is analogous to energy reserve, is one of the important clinical predictors in patients with dilated cardiomyopathy (DCM). However, it may vary with the cardiac workload.


METHODS
The myocardial PCr to beta-adenosine triphosphate ratio was measured before and during a 5 and 10 microgram/kg/min infusion of dobutamine in 7 patients with DCM and in 8 normal patients. Dobutamine infusion was kept constant for 50 minutes in each stage. Myocardial contractility and ventricular size were determined by echocardiography with the same protocol.


RESULTS
This ratio was unchanged from 1.5 +/- 0.4 to 1.8 +/- 0.6 in the low-dose stage and stable (1.7 +/- 0.3) in the high-dose stage in patients with DCM. The heart rate and the mean rate of circumferential fiber shortening increased dose dependently both in patients with DCM and in patients without.


CONCLUSIONS
These results demonstrate that constant loading of dobutamine for hours is tolerated without deterioration of myocardial metabolic function by patients with nonischemic DCM. We concluded that the high-energy phosphate metabolism of stable patients with cardiomyopathy is stable if the workload is temporary and weak. This implies the possibility that mild exercise can be tolerated in patients with heart failure.
Nanbu
T
T
Division of Cardiovascular Medicine, Date Red Cross Hospital, Sapporo, Japan.
Nakakoshi
T
T
Yonezawa
K
K
Kitabatake
A
A
D000255:Adenosine Triphosphate / Q000378:metabolism*; D002311:Cardiomyopathy, Dilated / Q000378:metabolism* / Q000503:physiopathology; D002316:Cardiotonic Agents / Q000008:administration & dosage; D004280:Dobutamine / Q000008:administration & dosage; D005260:Female; D006801:Humans; D007262:Infusions, Intravenous; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008875:Middle Aged; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000378:metabolism*; D010725:Phosphocreatine / Q000378:metabolism*; D013997:Time Factors; D016277:Ventricular Function, Left / Q000187:drug effects
D002316:Cardiotonic Agents; D010725:Phosphocreatine; D004280:Dobutamine; D000255:Adenosine Triphosphate