OBJECTIVES. To test the feasibility of myocardial angiogenic gene expression using a novel catheter-based transendocardial injection system. BACKGROUND. Angiogenesis has been induced by direct injection of growth factors into ischemic myocardium during open-heart surgery. Catheter-based transendocardial injection of angiogenic factors may provide equivalent benefit without need of surgery. METHODS. A new guidance system for intramyocardial therapy utilizes magnetic fields and catheter-tip sensors to locate a position in space and reconstruct three-dimensional left ventricular (LV) electromechanical maps without using fluoroscopy. A retractable 27G needle was coupled with the guidance system for LV transendocardial injection. In 12 pigs, the catheter was used to inject 0.1 ml of methylene-blue (MB) dye and 8 pigs had myocardial incjections of adenoviral vector (1 X 1010 particles per site) containing the LacZ transgene. Ten pigs underwent catheter-based transendocardial injection and six pigs were injected using transepicardial approach with the gene encoding adenovirus vascular endothelial growth factor-121 (Ad.VEGF121; 1 X 1010 viral particles X 6 sites) and sacrificed at 24 h. Injection sites were identified with ultraviolet light by coinjection of fluorescent beads. RESULTS. Overall, 138 of 152 attempted injection MB tracks (91%) were found after sacrifice. Tissue staining was 7.1 ± 2.1 mm in depth and 2.3 ± 1.8 mm in width. No animal had pericardial effusion or tamponade. In Ad.LacZ injected animals, gross pathology showed positive staining in injected zones, and histology confirmed positive myocyte staining. Adenovirus vascular endothelial growth factor-121 injected sites showed high levels of VEGF121 production that was of similar magnitude whether injected using the transendocardial (800.4 ± 412.2 pg VEGF121/mg protein) or transepicardial (838.3 ± 270 pg VEGF121/mg protein) delivery approach (p = 0.62). CONCLUSIONS. Using this magnetic guidance catheter-based navigational system, transgenes can effectively be transfected into designated myocardial sites. Thus, if it is determined that direct intramyocardial injection of angiogenic factors enhances collateral function in patients, this less invasive catheter- based system offers a similar gene delivery efficiency and, thus, may have clear advantages compared with the surgically-based transepicardial injection approach. (C) 2000 by the American College of Cardiology.