[Transfecting rat heart with human pacemaker gene in vivo to create a biological pacemaker]

To test the ability and safety of injecting the hHCN gene into the ventricle of intact rats to create a novel biological pacemaker and to explore the duration of the hHCN over-expression in vivo.

Adenoviral constructs incorporating hHCN4 and green fluorescent protein (GFP) were subepicardially injected into the rats' left ventricular wall in situ (n = 10). Control group was injected with adenoviral constructs of GFP alone (n = 10). ECGs were recorded every day within the initial three days after operation. Up to seven days after injection, all rats were anesthetized and subjected to cervical vagal trunks stimulation to permit the emergence of escape rhythm. Then pace-mapping was performed by the hand-hold electrode. Finally, hearts were removed for histology and immunofluorescence study.

Ventricular arrhythmic events were not found during the first three days. During vagal stimulation, the rate of spontaneous rhythm in the hHCN4-injected group was significantly more rapid than that in the control group (69 bpm +/- 6 bpm vs 41 bpm +/- 10 bpm, P < 0.001). Pace-mapping confirmed the escape rhythm in the hHCN4-injected group was originated near the injection site. Immunofluorescence study showed the overexpression of hHCN4 on the site of injection. However, the duration of hHCN overexpression was no more than one month after injection.

The overexpression of hHCN4 provides ventricular escape rhythm with the physiologically acceptable rate. Long-term feasibility of this approach needs to be tested.