Left ventricular ultrastructure in pulmonary stenosis and in tetralogy of Fallot

Summary Twelve patients underwent haemodynamic studies and myocardial biopsies: 7 with pulmonary stenosis (PS) and 5 with tetralogy of Fallot (TOF). Their ages ranged between 2 and 43 years. Right ventricular pressure was 128±43 mmHg in PS and 98±8 mmHg in TOF. Aortic blood oxygen saturation was 97.0%±1.4% in PS, and 88.4%±6.3% in TOF. Left ventricular (LV) weight was normal in TOF while it was increased in PS: 140.7±74.3 vs 74.0±8.7 g/m² (P<0.001). Contractility was altered in both PS and TOF: ejection fractions were 56%±7% vs 65%±6% (P<0.001). Light microscopy showed abnormal transverse diameter of left ventricular myocytes in both PS and TOF: 18.6 µm±4.0 µm vs 19.4 µ±4.9 µm. The percentage of interstitium was normal: 29.6%±3.9% vs 26.2%±5.1%. Transmission electron microscopic examination revealed hypertrophic changes in all patients and degeneration in 7 of them. Hyperfunctional alterations of the myocytes were characterized by the increased number and reduced size of mitochondria, the enlarged Golgi complex, the increased number of ribosomes, the marked folding and convolutions of the nuclear membrane, the dilatation and tortuosity of T tubules. Myofibrillar lysis was the major degenerative change, which was also observed in the right ventricle (RV) of the same patients. No correlation was observed between these alterations and the patient ages, RV pressures, aortic blood oxygen saturations and ejection fractions. These findings led us to conclude that: (1) suprasystemic pressure overload of the RV induces macroscopic LV hypertrophy; (2)mild and suprasystemic pressure overload of the RV induces hyperfunctional changes in the LV; (3)myocardial degenerationis not related to hypertrophy nor to hypoxia, but is part of a more widespread cardiovascular fetopathy.