Molecular enhancement of porcine cardiac chronotropy

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Abstract
OBJECTIVE To test the potential of gene transfer approaches to enhance cardiac chronotropy in a porcine system as a model of the human heart. METHODS Plasmids encoding either the human β2 adrenergic receptor or control constructs were injected into the right atria of native Yorkshire pig hearts. Percutaneous electrophysiological recording catheters equipped with 33 gauge circular injection needles were positioned in the mid-lateral right atrium. At the site of the earliest atrial potential the circular injection needles were rotated into the myocardium and the β2 adrenergic receptor (n = 6) or control plasmid constructs (n = 5) were injected. RESULTS Injection of the β2 adrenergic receptor construct significantly enhanced chronotropy compared with control injections. The average (SD) heart rate of the pigs was 108 (16) beats/min before injection. Two days after injection with control plasmids the heart rate was 127 (25) beats/min (NS compared with preinjection rates). After injection with plasmid encoding the β2 adrenergic receptor the heart rate increased by 50% to 163 (33) beats/min (p < 0.05 compared with preinjection and postinjection control rates). CONCLUSIONS The present studies showed in a large animal model that local targeting of gene expression may be a feasible modality to regulate cardiac pacemaking activity. In addition, these investigations provide an experimental basis for developing future clinical gene transfer approaches to upregulate heart rate and modulate cardiac conduction.