Progressive tissue iron deposition from multiple blood transfusions is common in beta-thalassaemia and pulmonary iron deposition may result in parenchymal damage. The objectives of this study were to: 1) determine the predominant pulmonary dysfunction in patients with thalassaemia major; and 2) demonstrate that parenchymal disease, if present, is at the level of the alveolocapillary membrane.Fourteen thalassaemia major patients (13 nonsmokers) receiving regular blood transfusion and without any history of chronic respiratory disease were recruited. Pulmonary function tests and echocardiography were performed before the scheduled transfusions. Three patients with the most restricted lung function were selected for high resolution computerized tomography (CT) of the lungs.One patient had an obstructive pattern with a forced expiratory volume in one second as percentage of forced vital capacity (FEV1/FVC) of 71%. Four patients demonstrated a restrictive pattern, as defined by total lung capacity (TLC) less than 80% predicted with normal FEV1/FVC%. Twelve patients had pulmonary transfer factors for carbon monoxide (TL,CO) below 80% pred, even after correction for the anaemia, indicating parenchymal disease. Eight of these 12 patients had alveolocapillary membrane defect, as demonstrated by a gas transfer factor of the pulmonary membrane (Tm) less than 80% pred. Mean resting arterial oxygen saturation was 95±2 (range 92-98) %. Eleven patients had oxygen desaturation of 5% or more during exercise on a bicycle ergometer, consistent with interstitial lung disease. There was no clinical or echocardiographic evidence of heart failure. Percentage predicted TLC was inversely correlated with age (r=-0.547; p=0.043). Both percentage predicted TLC and TL,CO were not correlated with iron burden or desferoxamine ratio. High resolution CT in the three selected patients showed no evidence of pulmonary fibrosis. We conclude that thalassaemia major patients have a predominant restrictive lung dysfunction with pulmonary parenchymal disease and alveolocapillary membrane block. The restrictive and interstitial lung disease could not be accounted for by iron loading or pulmonary fibrosis in our patients.

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To demonstrate the occurrence of concealed conduction in anomalous atrioventricular (AV) bypass tracts, 11 patients were selected for study. Two had a right-sided and nine had a left-sided bypass tract. Electrode catheters were placed in the right atrium, coronary sinus, AV junction and right ventricle. After every eighth atrial or ventricular driving beat (A1 or V1) at a constant cycle length, two successive atrial or ventricular premature beats (A2 and A3 or V2 and V3) were delivered. The A1A2 or V1V2 interval was fixed at 30 ms greater than the effective refractory period of the atrium or right ventricle, but less than the effective refractory period of the bypass tract in the anterograde or retrograde direction. This allows A2 or V2 to capture the atrium or ventricle, but not conduct in the bypass tract. The A3 or V3 was delivered from late diastole with a progressively shorter A2A3 or V2V3 interval until atrial or ventricular refractoriness was encountered. In the anterograde direction, the presence of A2 prevented A3 conduction in the bypass tract despite A1A3 intervals being longer than the anterograde effective refractory period of the bypass tract in 8 of the 11 patients. In the retrograde direction, the presence of V2 prevented V3 conduction in the bypass tract despite V1V3 intervals being longer than the retrograde effective refractory period of the bypass tract in 3 of the 11 patients. Thus, using the technique of programmed electrical stimulation, concealed conduction in anomalous AV bypass tracts can be demonstrated in both anterograde and retrograde directions.