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(Circulation. 2000;102:III-154.)
© 2000 American Heart Association, Inc.

Surgery for Congenital Heart Disease

Failure of Stroke Volume Augmentation During Exercise and Dobutamine Stress Is Unrelated to Load-Independent Indexes of Right Ventricular Performance After the Mustard Operation

Graham P. Derrick, BMedSci, BM, BS, MRCP; Indra Narang, BMedSci, BM, BS, MRCP; Paul A. White, PhD; Andrea Kelleher, BM, BS, FRCA; Andrew Bush, MD, FRCP; Daniel J. Penny, MD, MRCP; Andrew N. Redington, MD, FRCP

From the Great Ormond Street Hospital for Children (G.P.D., P.A.W., D.J.P., A.N.R.), Whipps Cross Hospital (I.N.), and Royal Brompton Hospital (A.K., A.B.), London, UK.

Correspondence to Professor Andrew Redington, Paediatric Cardiology Department, Great Ormond Street Hospital for Children, 28 Great Ormond St, London WC1N 3JH, UK. E-mail reding{at}ibm.net

Background—Impaired right ventricular function has been implicated as a cause of reduced maximal exercise capacity after the Mustard operation for transposition of the great arteries.

Methods and Results—Fourteen asymptomatic survivors of the Mustard operation were studied. Each underwent conventional cardiac catheterization, and after satisfactory hemodynamics were confirmed, load-independent indexes of ventricular function were derived by conductance catheter during dobutamine infusion (0, 5, and 10 µg · kg^-1 · min^-1). Seven patients also underwent upright exercise testing on a bicycle ergometer with analysis of respiratory gas exchange by continuous mass spectrometry. Accessible pulmonary blood flow was measured at each workload with an automated acetylene rebreathing technique. All patients exercised to a satisfactory end point (respiratory quotient >1.1). Maximum oxygen consumption during exercise was impaired compared with predicted values (mean, 77%; P<0.02). Both exercise and dobutamine infusion were associated with an increase in cardiac index and heart rate and a reduced stroke volume index response. This was despite significantly improved indexes of myocardial contraction (end-systolic pressure volume relation, P<0.001), preload recruitable stroke work index (P<0.01), VA coupling (P<0.001), and isovolumic relaxation (P<0.001) during dobutamine infusion. There were no changes observed in end-diastolic pressure-volume relations, but there was failure to augment ventricular filling manifest by absence of change in dV/dt (P=NS).

Conclusions—The stroke volume response to exercise stress is reduced in patients after the Mustard operation. A similar failure to augment stroke volume occurs during dobutamine stress despite appropriate responses in load-independent indexes of contraction and relaxation. This is due to failure to augment right ventricular filling rates during tachycardia, presumably as a result of impaired AV transport, consequent to the abnormal intra-atrial pathways.

Key Words: transposition of great vessels • hemodynamics • exercise

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