In the natural history of Thalassemia Major (Thal) with hemochromatosis, problems of conduction become increasingly prevalent. Intracardiac conduction intervals were measured during cardiac catheterization in 12 patients with Thal aged 11-28 years (mean 20.4 years) and compared to those of 13 normal individuals aged 14-17 years (mean 15.5 years). In Thal, hemoglobin values were 10.9 ± 1.6 Gm% at the time of study. Five of the Thal group were receiving digoxin for supraventricular arrhythmia and none were in heart failure. Normal subjects had: PH 92.2 ± 15.1 msec; AH 69.6 ± 16.5 msec; PA 23.2 ± 6.1 msec; HV 43.7 ± 6.4 msec.Significant differences were noted in Thal patients in PH and AH intervals: PH 135.0±30.0 msec (p< 0.001); AH 107.9 ± 27.1 msec (p< 0.001). The PA time [26.8 ± 9.5 msec] and HV interval [38.0 ± 5.7 msec] were similar to normal. There were no differences in any parameters between Thal patients receiving or not receiving digoxin, but those receiving digoxin had slightly longer intervals for PH and AH: PH 143.0 ± 21.1 msec vs 130.0 ± 35.6 msec (p< 0.001 vs p< 0.02 compared to normal) and AH 118.0 ± 16.8 msec vs 100.7 ± 31.8 msec (p<0.001 vs p<0.01 compared to normal). The subtle conduction delay through the AV nodal-to-His bundle area revealed by this study is the first clinical and electrophysiological documentation of deranged function and may be related to previous pathological studies showing deposits of iron in the AV nodal area in patients with hemochromatosis. Such delay may be the earliest manifestation of functional abnormality so common in adolescent and adult patients with Thalassemia Major.

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Levin, A., Engle, M., Ehlers, K. et al. 135 INTRACARDIAC CONDUCTION INTERVALS IN THALASSEMIA MAJOR. Pediatr Res 12, 386 (1978). https://doi.org/10.1203/00006450-197804001-00140

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