Feasibility of directional percutaneous epicardial ablation with a partially insulated catheter.

PURPOSE: To demonstrate the feasibility of directional percutaneous epicardial ablation using a partially insulated catheter. METHODS: Partially insulated catheter prototypes were tested in 12 (6 canine, 6 porcine) animal studies in two centers. Prototypes had interspersed windows to enable visualization of epicardial structures with ultrasound. Epicardial unipolar ablation and ablation between two electrodes was performed according to protocol (5-60 W power, 0-60 mls/min irrigation, 78 s mean duration). RESULTS: Of 96 epicardial ablation attempts, unipolar ablation was delivered in 53.1%. Electrogram evidence of ablation, when analyzable, occurred in 75 of 79 (94.9%) therapies. Paired pre/post-ablation pacing threshold (N = 74) showed significant increase in pacing threshold post-ablation (0.9 to 2.6 mA, P < .0001). Arrhythmias occurred in 18 (18.8%) therapies (11 ventricular fibrillation, 7 ventricular tachycardia), mainly in pigs (72.2%). Coronary artery visualization was variably successful. No phrenic nerve injury was noted during or after ablation. Furthermore, there were minimal pericardial changes with ablation. CONCLUSIONS: Epicardial ablation using a partially insulated catheter to confer epicardial directionality and protect the phrenic nerve seems feasible. Iterations with ultrasound windows may enable real-time epicardial surface visualization thus identifying coronary arteries at ablation sites. Further improvements, however, are necessary.

A Novel Defibrillation Tool: Percutaneously Delivered, Partially Insulated Epicardial Defibrillation.

INTRODUCTION: Epicardial defibrillation systems currently require surgical access. We aimed to develop a percutaneous defibrillation system with partially-insulated epicardial coils to focus electrical energy on the myocardium and prevent or minimize extra-cardiac stimulation. METHODS: We tested 2 prototypes created for percutaneous introduction into the pericardial space via a steerable sheath. This included a partially-insulated defibrillation coil and a defibrillation mesh with a urethane balloon acting as an insulator to the face of the mesh not in contact with the epicardium. The average energy associated with a chance of successful defibrillation 75% of the time (ED75) was calculated for each experiment. RESULTS: Of 16 animal experiments, 3 pig experiments had malfunctioning mesh prototypes such that results were unreliable; these were excluded. Therefore, 13 animal experiments were analyzed - 6 canines (29.8±4.0kg); 7 pigs (41.1±4.4kg). The overall ED75 was 12.8±6.7J (10.9±9.1J for canines; 14.4±3.9J in pigs [P=0.37]). The lowest ED75 obtained in canines was 2.5J while in pigs it was 9.5J. The lowest energy resulting in successful defibrillation was 2J in canines and 5J in pigs. There was no evidence of coronary vessel injury or trauma to extra-pericardial structures. CONCLUSION: Percutaneous, epicardial defibrillation using a partially insulated coil is feasible and appears to be associated with low defibrillation thresholds. Focusing insulation may limit extra-cardiac stimulation and potentially lower energy requirements for efficient defibrillation.

Evaluation of a Unique Defibrillation Unit with Dual-Vector Biphasic Waveform Capabilities: Towards a Miniaturized Defibrillator.

BACKGROUND: Automated external defibrillators can provide life-saving therapies to treat ventricular fibrillation. We developed a prototype unit that can deliver a unique shock waveform produced by four independent capacitors that is delivered through two shock vectors, with the rationale of providing more robust shock pathways during emergent defibrillation. We describe the initial testing and feasibility of this unique defibrillation unit, features of which may enable downsizing of current defibrillator devices. METHODS: We tested our defibrillation unit in four large animal models (two canine and two swine) under general anesthesia. Experimental defibrillation thresholds (DFT) were obtained by delivery of a unique waveform shock pulse via a dual-vector pathway with four defibrillation pads (placed across the chest). DFTs were measured and compared with those of a commercially available biphasic defibrillator (Zoll M series, Zoll Medical, Chelmsford, MA, USA) tested in two different vectors. Shocks were delivered after 10 seconds of stable ventricular fibrillation and the output characteristics and shock outcome recorded. Each defibrillation series used a step-down to failure protocol to define the defibrillation threshold. RESULTS: A total of 96 shocks were delivered during ventricular fibrillation in four large animals. In comparison to the Zoll M series, which delivered a single-vector, biphasic shock, the energy required for successful defibrillation using the unique dual-vector biphasic waveform did not differ significantly (P = 0.65). CONCLUSIONS: Our early findings support the feasibility of a unique external defibrillation unit using a dual-vector biphasic waveform approach. This warrants further study to leverage this unique concept and work toward a miniaturized, portable shock delivery system.

Beating Heart Validation of Safety and Efficacy of a Percutaneous Pericardiotomy Tool.

INTRODUCTION: Epicardial procedures frequently require pericardial manipulation. We aimed to develop a nonsurgical percutaneous pericardial modification tool that may (1) facilitate epicardial-based procedures by enabling adhesiolysis or (2) attenuate the myocardial constraining effect of the pericardium. METHODS: Three novel devices were developed to enable pericardiotomy, all of which can be deployed in over-the-wire fashion following percutaneous epicardial access. The grasper permits us to seize the pericardial membrane providing leverage for incision. The scissors enables anterograde cutting maneuvers. The reverse-slitter allows retrograde incisions; in addition, this device has a deflectable tip that increases the potential cutting area. We optimized these tools for safety by including electrodes to test for phrenic nerve stimulation as well as myocardial stimulation to determine directionality of the cutting devices. The base of the scissors and reverse-slitter are also blunt ensuring that the cutting element is always away from the myocardium. RESULTS: Following 5 nonbeating heart bench test experiments for prototype development, 11 animal (9 canine, 2 swine) studies were performed. Of these 2 were proof-of-concept open chest studies; the remaining 9 were entirely closed-chest, percutaneous procedures allowing for remodification of the prototypes. The tools successfully permitted incision of the pericardium in all studies. Hemodynamic measurements were assessed postincision and showed no compromise of systolic function. No coronary artery or phrenic nerve damage was seen in any study. CONCLUSION: Percutaneous pericardiotomy is feasible and appears to be safe. It may provide leverage in epicardial-based procedures and offer treatment options in disease processes characterized by pericardial restraint.

Blood Pressure Responses to Endovascular Stimulation: A Potential Therapy for Autonomic Disorders With Vasodilatation.

BACKGROUND: We have previously shown that sympathetic ganglia stimulation via the renal vein rapidly increases blood pressure. This study further investigated the optimal target sites and effective energy levels for stimulation of the renal vasculatures and nearby sympathetic ganglia for rapid increase in blood pressure. METHODS: The pre-study protocol for endovascular stimulations included 2 minutes of stimulation (1-150 V and 10 pulses per second) and at least 2 minutes of rest during poststimulation. If blood pressure and/or heart rate were changed during the stimulation, time to return to baseline was allowed prior to the next stimulation. RESULTS: In 11 acute canine studies, we performed 85 renal artery, 30 renal vein, and 8 hepatic vasculature stimulations. The mean arterial pressure (MAP) rapidly increased during stimulation of renal artery (95 ± 18 mmHg vs. 103 ± 15 mmHg; P < 0.0001), renal vein (90 ± 16 mmHg vs. 102 ± 20 mmHg; P = 0.001), and hepatic vasculatures (74 ± 8 mmHg vs. 82 ± 11 mmHg; P = 0.04). Predictors of a significant increase in MAP were energy >10 V focused on the left renal artery, bilateral renal arteries, and bilateral renal veins (especially the mid segment). Overall, heart rate was unchanged, but muscle fasciculation was observed in 22.0% with an output >10 V (range 15-150 V). Analysis after excluding the stimulations that resulted in fasciculation yielded similar results to the main findings. CONCLUSIONS: Stimulation of intra-abdominal vasculatures promptly increased the MAP and thus may be a potential treatment option for hypotension in autonomic disorders. Predictors of optimal stimulation include energy delivery and the site of stimulation (for the renal vasculatures), which informs the design of subsequent research.

Direct Pulmonary Vein Ablation With Stenosis Prevention Therapy.

INTRODUCTION: The dominant location of electrical triggers for initiating atrial fibrillation (AF) originates from the muscle sleeves inside pulmonary veins (PVs). Currently, radiofrequency ablation (RFA) is performed outside of the PVs to isolate, rather than directly ablate these tissues, due to the risk of intraluminal PV stenosis. METHODS: In 4 chronic canine experiments, we performed direct PV muscle sleeve RFA ± postablation drug-coated balloon (DCB) treatment with paclitaxel/everolimus. Of the 4 PVs, 2 PVs were ablated and treated with DCB, 1 PV was ablated without DCB treatment (positive control), and 1 PV was left as a negative control. Local electrograms were assessed in PVs for near-field signals and were targeted for ablation. After 12-14 weeks survival, PVs were interrogated for absence of near-field PV potentials, and each PV was assessed for stenosis. RESULTS: All canines survived the study period without cardiorespiratory complications, and remained ambulatory. In all canines, PVs that were ablated and treated with DCB remained without any significant intraluminal stenosis. In contrast, PVs that were ablated and not treated with DCB showed near or complete intraluminal stenosis. At terminal study, PV potentials remained undetectable. A blinded, histologic analysis demonstrated that ablated PVs without DCB treatment had extensive thrombus, fibrin, mineralization, and elastin disruption. CONCLUSION: Our chronic canine data suggest that direct PV tissue ablation without subsequent stenosis is feasible with the use of postablation DCBs.