Figure 1. Cardiomyocytes in infants with Tetralogy of Fallot with pulmonary stenosis (ToF/PS) fail to divide.

(A-C) Patients with Tetralogy of Fallot and pulmonary stenosis (ToF/PS) show an increased proportion of multinucleated (≥2) cardiomyocytes (filled symbols and solid lines in B). Each symbol in (B) and bar in (C) represents one human heart (ToF/PS: n = 12; No heart disease: n = 5). (D-F) A 4-week-old infant with ToF/PS was labeled with oral ¹⁵N-thymidine. Myocardium was analyzed by multiple-isotope imaging mass spectrometry (MIMS) at 7 months. (D-E) ³¹P reveals nuclei and ³²S morphologic detail, including striated sarcomeres. Nuclei are dark in the ³²S image. The ¹⁵N/¹⁴N ratio image reveals ¹⁵N-thymidine incorporation. The blue end of the scale is set to natural abundance (no label uptake) and the upper bound of the rainbow scale is set to 50% above natural abundance. The white arrows in (D) indicate the boundaries of a labelled mononucleated cardiomyocyte and in (E) the nuclei of a binucleated cardiomyocyte. (F) The percentage of labeled binucleated cardiomyocytes is higher than mononucleated cardiomyocytes (Mononucleated cardiomyocytes analyzed: n = 282; 15N+ mononucleated cardiomyocytes: n = 25; Binucleated cardiomyocytes analyzed: n = 104 (208 total nuclei); 15N+ binucleated cardiomyocytes: n = 20 (40 total nuclei)), indicating that this patient experienced extensive cytokinesis failure. Scale bar: 20 μm (A), 10 μm (D).