Cardiac myosin binding protein C regulates postnatal myocyte cytokinesis.

Homozygous cardiac myosin binding protein C-deficient (Mybpc(t/t)) mice develop dramatic cardiac dilation shortly after birth; heart size increases almost twofold. We have investigated the mechanism of cardiac enlargement in these hearts. Throughout embryogenesis myocytes undergo cell division while maintaining the capacity to pump blood by rapidly disassembling and reforming myofibrillar components of the sarcomere throughout cell cycle progression. Shortly after birth, myocyte cell division ceases. Cardiac MYBPC is a thick filament protein that regulates sarcomere organization and rigidity. We demonstrate that many Mybpc(t/t) myocytes undergo an additional round of cell division within 10 d postbirth compared with their wild-type counterparts, leading to increased numbers of mononuclear myocytes. Short-hairpin RNA knockdown of Mybpc3 mRNA in wild-type mice similarly extended the postnatal window of myocyte proliferation. However, adult Mybpc(t/t) myocytes are unable to fully regenerate the myocardium after injury. MYBPC has unexpected inhibitory functions during postnatal myocyte cytokinesis and cell cycle progression. We suggest that human patients with homozygous MYBPC3-null mutations develop dilated cardiomyopathy, coupled with myocyte hyperplasia (increased cell number), as observed in Mybpc(t/t) mice. Human patients, with heterozygous truncating MYBPC3 mutations, like mice with similar mutations, have hypertrophic cardiomyopathy. However, the mechanism leading to hypertrophic cardiomyopathy in heterozygous MYBPC3(+/-) individuals is myocyte hypertrophy (increased cell size), whereas the mechanism leading to cardiac dilation in homozygous Mybpc3(-/-) mice is primarily myocyte hyperplasia.

Long-Term Prognosis of Different Subtypes of Left Ventricular Noncompaction Cardiomyopathy Patients: A Retrospective Study in China.

Left ventricular noncompaction (LVNC) is a heterogeneous cardiomyopathy that can be classified into different subtypes based on morphologic and functional features. However, the prognosis of the dilated and isolated subtypes of non-pediatric LVNC remains unknown. We retrospectively studied 101 patients with LVNC diagnosed at Peking Union Medical College Hospital from 2006 to 2022 using the Jenni criteria of transthoracic echocardiography. The patients were grouped into those with dilated LVNC (n = 64) or isolated LVNC (n = 37), and 88 patients (54 with dilated LVNC and 34 with isolated LVNC) were followed up successfully. The primary outcome was major adverse cardiovascular events (a composite of cardiovascular mortality, heart failure, severe ventricular arrhythmia, and systolic embolism). The median follow-up time was 5.24 years. The incidence of major adverse cardiovascular events was 43.2%; patients with dilated LVNC had a higher risk (adjusted hazard ratio, 4.43; 95% confidence interval, 1.24-15.81; p = 0.02) than those with isolated LVNC. None of the isolated LVNC patients had cardiovascular deaths or severe ventricular arrhythmias. The risk of systemic embolism was similar between patients with dilated and isolated LVNC. Our findings indicate that transthoracic echocardiography is a useful tool for classifying LVNC into subtypes with distinct clinical outcomes. Dilated LVNC is associated with a poor prognosis, while the isolated subtype is probably a physiological condition.

Indirect Blood Pressure Measurement in Horses: Is There an Influence of Age, Sex, Breed, Bodyweight, and Cardiac Diseases on Pressure Values?

Only few data regarding normal resting blood pressure in horses and the influence of cardiac diseases on arterial blood pressure are available in literature. The purpose of the present study was to investigate the possible influence of age, sex, breed, bodyweight, and cardiac diseases and their severity on blood pressure values measured in horses with cardiac disease and in a control group. For this case-control study, indirect blood pressure measurement was performed in 60 horses with different types of cardiac disease and in 23 healthy horses (control group), by means of an ultrasonic blood-flow technique. According to the echocardiographic findings, horses with cardiac abnormalities have been divided into two groups (with and without cardiac dimensional modifications). Multivariable linear regression analysis evaluated the influence of age, breed, sex, and cardiac diseases and their severity (regressors) on blood pressure. The results showed a significant influence of age on diastolic pressure in healthy horses. Furthermore, a significant influence of the presence of cardiac dilation in horses with cardiac disease on systolic and diastolic pressures was found. Single-regressor linear analysis showed that horses with cardiac dilation are significantly older than both horses without cardiac dimensional changes and those of control group. Further studies are necessary to better investigate the possible influence of the type of cardiac disease on blood pressure.