Radiofrequency applications in congenital heart disease

The relatively recent application of radiofrequency technologies in the treatment of congenital heart defects has provided a safe and effective alternative to conventional therapies in establishing endovascular patency for a variety of lesions. Radiofrequency, with typically used frequencies of approximately 500 kHz, does not cause pain and is unlikely to induce atrial or ventricular fibrillation. It can be used either to ablate (higher power (35-50 W); longer duration of application (90-120 sec); lower voltage (30-50 V)) or to perforate (lower power (5-10 W) shorter duration of application (1-5 sec), higher voltage (150-280 V)). In the past, perforating radiofrequency has been applied to establish right ventricular outflow tract patency in pulmonary atresia with intact septum and with ventricular septal defect. More recently radiofrequency has been shown to be effective at recanalizing central and peripheral vasculature and has also been applied in establishing percutaneous left heart access. A new radiofrequency catheter, dedicated to transseptal left atrial cannulation, has been demonstrated to be safe and effective in an animal model and is now ready for clinical trials.     

Non-contact mapping guided cardiac resynchronization therapy for a failing systemic right ventricle.

AIMS: Progressive systemic right ventricular (sRV) dysfunction, atrial and ventricular arrhythmias and sudden cardiac death are well-recognized late sequelae of atrial redirection surgery in which the right ventricle is left connected to the systemic circulation. Although cardiac resynchronization therapy (CRT) poses an attractive therapeutic option, little is known about indications, patient selection, and technical aspects of best lead placement. METHODS AND RESULTS: We undertook CRT in a 27-year-old female patient post-Mustard correction for d-transposition (d-TGA) with New York Heart Association (NYHA) grade III disability with QRS duration measuring 130 ms. There was also echocardiographic (TTE) evidence of severe sRV dysfunction. Non-contact mapping (NCM) was used to define sites of late activation within the sRV and the acute intra-arterial blood pressure (BP) response was assessed during implantation of a 4 french (F) lead onto the endocardial surface of the sRV. At 4 weeks post-implant sRV lateral wall motion had improved and the ejection fraction (EF) rose from 23 to 33%. The patient has been successfully anticoagulated and improved to NYHA II status after 6 months. CONCLUSION: The use of NCM proved safe and effective and provided a qualitative assessment of electrical viability of the sRV complimenting the measurement of mechanical function provided by TTE. The favourable clinical response in the above case justifies a prospective evaluation of this strategy.     

Cardiac defibrillation therapy for at risk patients with systemic right ventricular dysfunction secondary to atrial redirection surgery for dextro-transposition of the great arteries.

AIM: To review techniques of implantable cardioverter-defibrillators (ICD) in patients after Mustard surgery for arterial transposition. METHODS AND RESULTS: Retrospective analysis of all Mustard patients receiving ICDs at our institution. Five patients (median age 24 years, range 19-35, 3 male) with systemic right ventricular dysfunction (sRV) dysfunction and New York Heart Association (NYHA) II and III, received ICDs. Implantation was performed transvenously in three patients, epicardial patches and subcutaneous arrays at surgery in two patients. Two patients required lead extraction and baffle stent angioplasty before ICD implantation. Defibrillation vectors incorporating the anterior sRV mass [i.e., sub-pulmonary left ventricle (pLV) to generator can, and between epicardial defibrillator patches], consistently achieved a minimum 10 joule(J) safety margin during defibrillation threshold (DFT) testing. Subcutaneous arrays and endocardial vectors that included a superior vena cava (SVC) electrode were less effective. One patient developed pulmonary oedema post-procedure. At a median 20 months, all patients were alive and in NYHA class II. Follow-up over 24 months documented multiple non-sustained ventricular tachycardia (VT) in the group and one patient had recurrent VT with aborted device therapy. CONCLUSION: Defibrillator implantation in Mustard patients is challenging. Sub-optimal defibrillation should be anticipated and can be overcome using vectors which integrate the RV mass and high-energy devices. A staged procedure involving pre-implant interventions or separate DFT tests, where indicated, may be better tolerated by patients.