Effects of metoprolol therapy on cardiac gap junction remodelling and conduction in human chronic atrial fibrillation

BACKGROUND AND PURPOSE

We investigated the influence of metoprolol on gap junction proteins connexin43 (Cx43) and connexin40 (Cx40) in atrial tissue from patients with/without atrial fibrillation (AF).

EXPERIMENTAL APPROACH

Left atrial tissue samples from 160 patients with AF or sinus rhythm (SR) with or without metoprolol (mean daily dose: 65.2 ± 9.1 mg·day⁻¹) were analysed for Cx43 and Cx40 by Western blot and immunohistology. Transverse and longitudinal conduction velocities were determined by 64 multi-electrode mapping.

KEY RESULTS

Both Cx43 and Cx40 expression were significantly increased in patients with AF versus SR. Cx43-expression in AF was significantly higher in patients receiving metoprolol, while Cx40 expression was unaffected by metoprolol treatment. In AF, the ratio of lateral/polar expression of Cx43 and Cx40 was enhanced due to increased expression at the sides of the cells (lateral) and a loss at the cell poles. This AF-induced increase in lateral/polar expression of Cx43, but not of Cx40, was significantly antagonized by metoprolol treatment. Functionally, in AF patients, transverse conduction velocity in atrial samples was significantly enhanced and this change was also significantly antagonized by metoprolol.

CONCLUSIONS AND IMPLICATIONS

AF induced enhanced lateral expression of Cx43 and Cx40 together with enhanced transverse conduction velocity in left atrial tissue. Alterations in localization of Cx43 and conduction changes were both antagonized by metoprolol, showing that pharmacological modulation of gap junction remodelling seems, in principle, possible. This finding may open new approaches to the development of anti-arrythmic drugs.

Rupture of the papillary muscle of the tricuspid valve - echocardiographic diagnosis of a rare anomaly leading to critical tricuspid valve regurgitation in the newborn

We present the case of a male full-term neonate who presented at 4 h of age with severe cyanosis unresponsive to mechanical ventilation and oxygen supplementation. The diagnosis of rupture of the papillary muscle of the tricuspid valve was made by echocardiography. Preoperative stabilization was achieved by adding nitric oxide and extracorporeal membrane oxygenation therapy could be avoided. Corrective surgery was successfully performed on the 7th day of life. Follow-up examination at 2 months of age revealed an excellent postoperative result. Perinatal rupture of the papillary muscle and/or chordae tendineae of the tricuspid valve is exceedingly rare and usually lethal when untreated or diagnosed late. Therefore, timely diagnosis is mandatory for adequate preoperative management and subsequent surgical treatment.