Catheter-Free Arrhythmia Ablation Using Scanned Proton Beams: Electrophysiologic Outcomes, Biophysics, and Characterization of Lesion Formation in a Porcine Model.

BACKGROUND: Proton beam therapy offers radiophysical properties that are appealing for noninvasive arrhythmia elimination. This study was conducted to use scanned proton beams for ablation of cardiac tissue, investigate electrophysiological outcomes, and characterize the process of lesion formation in a porcine model using particle therapy. METHODS: Twenty-five animals received scanned proton beam irradiation. ECG-gated computed tomography scans were acquired at end-expiration breath hold. Structures (atrioventricular junction or left ventricular myocardium) and organs at risk were contoured. Doses of 30, 40, and 55 Gy were delivered during expiration to the atrioventricular junction (n=5) and left ventricular myocardium (n=20) of intact animals. RESULTS: In this study, procedural success was tracked by pacemaker interrogation in the atrioventricular junction group, time-course magnetic resonance imaging in the left ventricular group, and correlation of lesion outcomes displayed in gross and microscopic pathology. Protein extraction (active caspase-3) was performed to investigate tissue apoptosis. Doses of 40 and 55 Gy caused slowing and interruption of cardiac impulse propagation at the atrioventricular junction. In 40 left ventricular irradiated targets, all lesions were identified on magnetic resonance after 12 weeks, being consistent with outcomes from gross pathology. In the majority of cases, lesion size plateaued between 12 and 16 weeks. Active caspase-3 was seen in lesions 12 and 16 weeks after irradiation but not after 20 weeks. CONCLUSIONS: Scanned proton beams can be used as a tool for catheter-free ablation, and time-course of tissue apoptosis was consistent with lesion maturation.

External Arrhythmia Ablation Using Photon Beams: Ablation of the Atrioventricular Junction in an Intact Animal Model.

BACKGROUND: This study sought to investigate external photon beam radiation for catheter-free ablation of the atrioventricular junction in intact pigs. METHODS AND RESULTS: Ten pigs were randomized to either sham irradiation or irradiation of the atrioventricular junction (55, 50, 40, and 25 Gy). Animals underwent baseline electrophysiological evaluation, cardiac gated multi-row computed tomographic imaging for beam delivery planning, and intensity-modulated radiation therapy. Doses to the coronary arteries were optimized. Invasive follow-up was conducted ≤4 months after the irradiation. A mean volume of 2.5±0.5 mL was irradiated with target dose. The mean follow-up length after irradiation was 124.8±30.8 days. Out of 7 irradiated animals, complete atrioventricular block was achieved in 6 animals of all 4 dose groups (86%). Using the same targeting margins, ablation lesion size notably increased with the delivered dose because of volumetric effects of isodose lines around the target volume. The mean macroscopically calculated atrial lesion volume for all 4 dose groups was 3.8±1.1 mL, lesions extended anteriorly into the interventricular septum. No short-term side effects were observed. No damage was observed in the tissues of the esophagus, phrenic nerves, or trachea. However, histology revealed in-field beam effects outside of the target volume. CONCLUSIONS: Single-fraction doses as low as 25 Gy caused a lesion with interruption of cardiac impulse propagation using this respective target volume. With doses of ≤55 Gy, maximal point-doses to coronary arteries could be kept <7Gy, but target conformity of lesions was not fully achieved using this approach.

Flat-panel detectors in the cardiac catheterization laboratory: revolution or evolution-what are the issues?

Continuous developments in digital imaging technology have contributed to the vital role held today by digital X-ray imaging in the cardiac catheterization laboratory. Foremost among these developments is the replacement of cine film with digital data equivalents as the procedure record. Other improvements include software innovations and processing algorithms, along with new types of hardware capable of delivering required functionality more rapidly. A significant recent development is that of the flat-panel X-ray detector as a replacement for the image intensifier, which has served the needs of the cardiac catheterization laboratory for nearly 5 decades. Clinical users must evaluate the respective technologies and determine whether one or the other meets the needs of their own laboratories. In this review, the two competing detector technologies are reviewed and a summary of general advantages and disadvantages of each is provided. A qualitative description is provided of parameters that can be used to assess quantitatively the performance of detectors and imaging systems. Using such objective measurements, together with standard techniques for evaluating imaging systems, angiographers and managers can better arrive at informed decisions for their own situation.

Low-risk percutaneous coronary interventions without on-site cardiac surgery: two years' observational experience and follow-up.

BACKGROUND: We studied the safety and efficacy of performing low-risk elective and acute infarct percutaneous coronary interventions at a community hospital without cardiac surgical capability. METHODS: Immanuel St Joseph's Hospital is located 85 miles from St Mary's Hospital, which is the nearest center with on-site cardiac surgery. All components of the Mayo Clinic percutaneous coronary intervention program were replicated at Immanuel St Joseph's Hospital, including a telemedicine system to enable real-time consultation with interventional and cardiac surgical colleagues during procedures. RESULTS: From March 1999 to June 2001, 196 patients underwent elective percutaneous coronary intervention at Immanuel St Joseph's Hospital. Procedural success was achieved in 195 (99.5%) patients, with 1 (0.5%) inhospital death. At mean follow-up of 8.2 months, 2 (1.0%) additional patients died of noncardiac causes and 15 (7.7%) patients required target vessel revascularization. From March 2000 to June 2001, 89 patients underwent primary percutaneous coronary intervention for acute myocardial infarction. Procedural success was achieved in 83 (93.3%) patients, with 3 (3.4%) inhospital deaths. At 30-day follow up, no additional patients died, had recurrent myocardial infarction, or required target vessel revascularization. No patients required transfer to another facility for emergent cardiac surgery for a procedure-related complication. CONCLUSIONS: Low-risk elective and acute infarct percutaneous coronary interventions can be performed with safety and efficacy at a community hospital without cardiac surgical capability by following rigorous standards.