BRIEF COMMUNICATIONS Pulmonary Vascular Resistance and Reactivity in Children with End-Stage Cardiomyopathy Marina L. Hughes, PhD, FRACP, a Sabine Kleinert, MD, a Anne Keogh, MD, FRACP, b Peter Macdonald, PhD, b James L. Wilkinson, FRCP, FACC, a and Robert G. Weintraub, FRACP a Pulmonary vascular resistance (PVR) and reactivity were compared in 63 children with end-stage cardiomyopathy (CM) referred for cardiac transplantation. Diagnostic category of CM was the sole determinant of PVR. Compared with other patients, children with restrictive CM were younger at diagnosis and had a significantly higher pulmonary vascular resistance index (PVRI). Children with a baseline PVRI of up to 11.8 units per meter squared (U.m 2 ) who showed reactivity underwent successful orthotopic cardiac transplantation. J Heart Lung Transplant 2000;19:701–704. High pulmonary vascular resistance (PVR) in patients with cardiomyopathy (CM) is associated with decreased survival before and after cardiac transplantation. 1,2 Among adult patients with CM, the principal factor associated with elevated PVR is diastolic dysfunction, 3 with the development of re- strictive physiology. 4 Little is known about the fac- tors that influence PVR in children with CM. This study examines potential determinants of PVR in a cohort of young patients with end-stage CM, re- ferred for cardiac transplantation. METHODS The study population comprised all patients aged 0 to 20 years with CM involving the left ventricle and who were referred to the Royal Children’s Hospital, Melbourne or St. Vincent’s Hospital, Sydney, be- tween 1984 and 1998, for consideration of cardiac transplantation, and for whom cardiac catheteriza- tion data were available. Patients were assigned to 1 of 3 diagnostic categories: dilated cardiomyopathy (DCM), hypertrophic cardiomyopathy (HCM), or restrictive cardiomyopathy (RCM), according to es- tablished criteria 5 and based on the results of car- diac catheterization and/or echocardiography. Right-sided cardiac catheterization and cardiac out- put studies were undertaken on all children as part of the pre-transplant workup. Cardiac output was measured by thermodilution, or in a minority of cases, by the Fick method, using an assumed oxygen consumption. 6 The pulmonary vascular resistance index (PVRI) was calculated as the difference be- tween the mean pulmonary artery and pulmonary wedge pressures, divided by cardiac index, and expressed as U.m 2 . Pulmonary vascular reactivity was assessed if significantly elevated pulmonary vascular resistance was found. During the study period, a variety of agents were employed (Figure), though inhaled nitric oxide in doses of 10 to 80 ppm was used exclusively after 1993. The vasodilator challenge involved repeating the above measure- From the Department of Cardiology, a Royal Children’s Hospital, Melbourne, Australia; and Heart and Lung Transplant Unit, b St. Vincent’s Hospital, Sydney, Australia. Submitted October 25, 1999; accepted April 25, 2000. Reprint requests: Robert G. Weintraub, FRACP, Department of Cardiology, Royal Children’s Hospital, Flemington Road, Parkville, Victoria 3052, Australia. Telephone: 61-3-9345 5718. Fax: 61-3-9345 6001. E-mail: weintrar@cryptic.rch.unimelb. edu.au Copyright © 2000 by the International Society for Heart and Lung Transplantation. 1053-2498/00/$–see front matter PII S1053-2498(00)00118-2 701