Contact force guided radiofrequency current application at developing myocardium.

INTRODUCTION: Catheter contact is a key determinant for lesion size in radiofrequency catheter ablation (RFA). Monitoring of contact force (CF) during RFA has been shown to improve efficacy of RFA in experimental settings as well as in adult patients. Coronary artery narrowing after RFA has been described in experimental settings as well as in children and adults and may be dependent from catheter contact. The value of CF monitoring concerning these issues has not been systematically studied yet. Value of high versus low CF during RFA in piglets was studied to assess lesion size and potential coronary artery involvement mimicking RFA in small children. METHODS: RFA with continuous CF monitoring was performed in 24 piglets (median weight 18.5 kg) using a 7 F TactiCath Quartz radiofrequency (RF) ablation catheter (Abbott). A total of 7 lesions were induced in each animal applying low (10-20 g) or high (40-60 g) CF. RF energy was delivered with a target temperature of 65°C at 30 W for 30 s. Coronary angiography was performed prior and immediately after RF application. Animals were assigned to repeat coronary angiography followed by heart removal after 48 h (n = 12) or 6 months (n = 12). Lesions with surrounding myocardium were excised, fixated, and stained. Lesion volumes were measured by microscopic planimetry. RESULTS: A total of 148 RF lesions were identified in the explanted hearts. Only in the subset of lesions at the AV annulus 6 month after ablation, lesion size and number of lesions exhibiting transmural extension were higher in the high CF group compared to low CF. In all other locations CF had no impact on lesion size and mural extension after 48 h as well as after 6 months. Additional parameters such as lesion size index and force time integral were also not related to lesion size. Coronary artery damage was present in two animals after 48 h and in one after 6 months and was not related to CF. CONCLUSION: In our experimental setting, lesion size in piglets was not related to catheter CF. Transmural extension of the RF lesions involving the layers of the coronary arteries was frequently noted irrespective of CF. Coronary artery narrowing was present in 3/24 animals and was not related to CF. In infants and toddlers, low CF (10-20 g) may be of adequate effect. Impact of CF monitoring during conventional RF ablation in children requires further investigation.

Epicardial implantation of a leadless pacemaker in a lamb model.

BACKGROUND: Pacemaker used in small children typically consist of an abdominally placed generator and epicardially affixed leads, making such a system prone to lead dysfunction during growth. Aim of this study was to investigate the feasibility of epicardial pacing with a leadless pacemaker in a lamb model. ANIMALS AND METHODS: Seventeen lambs underwent epicardial implantation of a Micra transcatheter pacing system (TPS) (Medtronic, Minneapolis, MN, USA) via left-lateral thoracotomy to the left ventricle (LV) surface (n = 11/17) and to the left atrial appendage (n = 6). Ventricular devices were fixated with the tines within the pericardium, whereas the tines of the atrial devices penetrated the myocardium of the left atrial appendage. After 31 weeks, animals were sacrificed and hearts were explanted for histological analysis. RESULTS: Following implantation, median P/R amplitude was 4.25/5.5 mV while median pacing threshold was 1.1/1.9 V at 0.24 ms. After 31 weeks, median P/R amplitude was 3.3/4.2 mV. Median atrial pacing threshold was 0.5/0.24 ms. Eight of 10 ventricular pacemakers had lost capture at standard impulse width even at maximum impulse amplitude. On explantation, firm adhesion of the device to the thoracic wall and dislodgement of the electrode tip was found in those ventricular devices. CONCLUSIONS: Firm fixation of the Micra electrode to the epicardial surface as applied to the atrial devices resulted in excellent electrical properties during midterm follow up. Pericardial fixation as in the ventricular devices was associated with loss of capture. Therefore, it is important to embed the tines in the myocardium and to choose an alternative implantation site allowing for safe fixation of the Micra TPS in a position perpendicular to ventricular epimyocardium.