Biological pacemaker implanted in canine left bundle branch provides ventricular escape rhythms that have physiologically acceptable rates.
BACKGROUND
We hypothesized that administration of the HCN2 gene to the left bundle-branch (LBB) system of intact dogs would provide pacemaker function in the physiological range of heart rates.


RESULTS
An adenoviral construct incorporating HCN2 and green fluorescent protein (GFP) as a marker was injected via catheter under fluoroscopic control into the posterior division of the LBB. Controls were injected with an adenoviral construct of GFP alone or saline. Animals were monitored electrocardiographically for up to 7 days after surgery, at which time they were anesthetized and subjected to vagal stimulation to permit emergence of escape pacemakers. Hearts were then removed and injection sites visually identified and removed for microelectrode study of action potentials, patch clamp studies of pacemaker current, and/or immunohistochemical studies of HCN2. For 48 hours postoperatively, 7 of 7 animals subjected to 24-hour ECG monitoring showed multiple ventricular premature depolarizations and/or ventricular tachycardia attributable to injection-induced injury. Thereafter, sinus rhythm prevailed. During vagal stimulation, HCN2-injected dogs showed rhythms originating from the left ventricle, the rate of which was significantly more rapid than in the controls. Excised posterior divisions of the LBB from HCN2-injected animals manifested automatic rates significantly greater than the controls. Isolated tissues showed immunohistochemical and biophysical evidence of overexpressed HCN2.


CONCLUSIONS
A gene-therapy approach for induction of biological pacemaker activity within the LBB system provides ventricular escape rhythms that have physiologically acceptable rates. Long-term stability and feasibility of the approach remain to be tested.
Plotnikov
Alexei N
AN
Center for Molecular Therapeutics, Department of Pharmacology, College of Physicians and Surgeons of Columbia University, New York, NY 10032, USA.
Sosunov
Eugene A
EA
Qu
Jihong
J
Shlapakova
Iryna N
IN
Anyukhovsky
Evgeny P
EP
Liu
Lili
L
Janse
Michiel J
MJ
Brink
Peter R
PR
Cohen
Ira S
IS
Robinson
Richard B
RB
Danilo
Peter
P
Rosen
Michael R
MR
D000200:Action Potentials; D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000209:etiology / Q000503:physiopathology* / Q000628:therapy; D004285:Dogs; D004558:Electric Stimulation; D004562:Electrocardiography; D005260:Female; D015316:Genetic Therapy; D005822:Genetic Vectors; D049452:Green Fluorescent Proteins; D006329:Heart Conduction System; D006352:Heart Ventricles / Q000503:physiopathology*; D006406:Hematoma / Q000209:etiology / Q000473:pathology; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D007473:Ion Channels / Q000032:analysis / Q000235:genetics*; D008164:Luminescent Proteins / Q000235:genetics; D008297:Male; D009124:Muscle Proteins / Q000032:analysis / Q000235:genetics*; D032383:Myocytes, Cardiac / Q000502:physiology; D010138:Pacemaker, Artificial; D018408:Patch-Clamp Techniques; D010507:Periodicity; D011690:Purkinje Fibers / Q000166:cytology
D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D007473:Ion Channels; D008164:Luminescent Proteins; D009124:Muscle Proteins; D049452:Green Fluorescent Proteins