Cadiology Journal Club Hardik Bhansali , MD PGY-2
Implantable Cardioverter-Defibrillators - Established therapy for the prevention of death from ventricular arrythemia - Conventional ICD use transvenous leads for cardiac sensing and defibrillation - Complications mainly associated with lead insertion include pneumothorax, hemothorax, cardiac temponade. - Difficulties in achieving venous access can prolong the procedure and result in failed ICD implantation. - Lead failure results in inappropriate shocks or impedes appropriate therapy. Removal of the failed lead is associated with substantial morbidity. - If cardiac pacing is not necessary, then it may be beneficial to avoid transvenous electrodes (for sensing and therapy) by using an entirely subcutaneous ICD system.
Study Design: - Two short-term trials of temporarily inserted subcutaneous ICD electrode system f/b - Two long-term trials of subcutaneous ICD implantation of a fully functional system. - Studies sponsored by Cameron Health, manufacturer of subcutaneous ICD and designed by investigators. - All study participants satisfied standard criteria for ICD implantation and provided informed consent. - Study data were collected by investigators and device data were provided by the sponsor.
Evaluation of lead configuration: - From Sep 2001 to Feb 2004, short-term defibrillation trial to identify the best electrode configuration for subcutaneous ICD. - Four electrode configuration were selected on the basis of the use of specific anatomical landmarks. - 78 patients participated, each patient underwent temporary subcutaneous implantation of one or more of the four device configurations and testing of the defibrillation threshold. - After completion of the study, all temporary subcutenous devices were explanted and each patient underwent implantation of conventional transvenous ICD.
Comparison of temporary subcutaneous ICD with transvenous ICD: - From Apr 2004 to Jun 2005, short-term trial involving 49 patients, best of the tested subcutaneous ICD system was compared with transvenous ICD system. - Both the subcutaneous and transvenous devices were implanted during the same procedure. - Defibrillation thresholds were compared after both systems were in position and both surgical pockets had been closed. - The system that was tested first was selected randomly. - After completion of the study, the subcutaneous device was explanted.
Permanent Implantation: - Two trials of permanent subcutaneous ICD implantation. - Pilot trial of 6 patients who underwent implantation in Jul 2008 f/b trial of 55 patients who underwent implantation between Dec 2008 to Feb 2009. - Inclusion Criteria – class I, IIa and IIb indication for ICD therapy - Exclusion Criteria – GFR < 30 ml/min Requirement for antibradycardia pacing H/O VTach < 170 bpm Documented VTach known to be reliably terminated with antitachycardia pacing - Primary end point was conversion of two consecutive episodes of induced VFib, with a single 65 J shock.
Subcutaneous ICD System: - 3 mm tripolar parasternal electrode connected to an electrically active pulse generator. - Electrode - parallel to and 1 to 2 cm to the left of the sternal midline - 8 cm shocking coil, flanked by two sensing electrodes - distal sensing electrode adjacent to manubriosternal junction - proximal sensing electrode adjacent to xiphoid process - Pulse Generator – over sixth rib between MAL and AAL - The insertion is guided by anatomical landmarks, no flouroscopy is required.
Subcutaneous ICD System: - Rhythm is detected by two sensing electrodes and the pulse generator. - ICD selects an appropriate vector for rhythm detection and for avoiding double QRS counting and T-wave oversensing. - signals determined for noise and double detection. - Feature analysis and rate detection to sort rhythm and need for therapy. - Discrimination Zone - Capacitor charging to avoid delivery of shocks for NSVT - Energy – 65 J to 80 J - Reverse shock polarity automatically - Demand pacing at 50 bpm, after > 3.5 s of post-shock asystole
Subcutaneous ICD System: - Automated device settings except for shock therapy pacing after shock conditional discrimination of SVT upper rate cut-off - Data storage has pre-event EKG and rhythm markers. Upto 24 treated episodes can be stored (each for 120 seconds)
Results: (1) Evaluation of lead configuration No of patients: 78 (72 men) Mean age: 61 +/- 11 years (range 31 to 80) Weight: 82.4 +/- 15.2 kg (range 53 to 143.5 kg) Mean EF: 0.35 +/- 0.14 (range 0.10 to 0.69) - left lateral pulse generator with the 8 cm parasternal coil electrode had the lowest mean defibrillation threshold.
Results: (2) Temporary Subcutaneous ICD versus Transvenous ICD No of patients: 49 (47 men) Mean age: 64 +/- 11 years (range 42 to 79) Weight: 85.3 +/- 12.8 kg (range 61 to 114 kg) Mean EF: 0.37 +/- 0.13 (range 0.19 to 0.70)
Results: (2) Temporary Subcutaneous ICD versus Transvenous ICD
(3) Permanent Subcutaneous ICD Pilot Study No of patients: 6 (6 men) Mean age: 60 +/- 11 years (range 46 to 72) Weight: 99 +/- 12 kg (range 87 to 114 kg) Mean EF: 0.23 +/- 0.07 (range 0.15 to 0.35) CAD: 5 patients NICM: 1 patient Cardiac Surgery: 2patients - All patients had successful implantation of ICD and defibrillation with 65 J submaximal shocks was successful during two consecutive episodes of induced VFib - Total 18 episodes of VFib were induced (100% detection) - After 488 days of f/u no spontaneous VFib/VTach episodes occurred with no device related complications or inappropriate shocks.
Results: (4) European Clinical Trial - 65 patients satisfied the enrollment criteria - 8 patients declined to participate in the study - 2 patients were chosen for Transvenous ICD as per patient's physician - Finally 55 patients were enrolled and all received a subcutaneous ICD - Defibrillation testing wasn't possible in 2 patients due to hemodynamic instablity and failure to induce VFib. So, 53 patients were evaluated for sensing and defibrillation. - 137 episodes of induced VFib (100% detection) - In 52/53 patients, two consecutive episodes induced arrythemias were converted as 65 J.
Results: (4) European Clinical Trial - Conversion achieved with standard polarity in 50 patients and with reverse polarity in 2 patients. - 53 rd patient, defibrillation at 65 J was achieved during the first induction, but not during the second induction. Patient then received a transvenous ICD. - Shock Delivery Time: 14 +/- 2.5 seconds - Procedure Time: 67 +/- 33 min -> 55 +/- 23 min - 12 episodes of spontaneous VTach were detected and treated successfully including VT Storm. - 54/55 patients alive after 10 months of f/u, 1 death from CRF
Results: (4) European Clinical Trial Complications - pocket infection (2) - no pocket erosion, no lead fractures, no lead dpgrade - lead migration (2), lead dislodgement (3) - Oversensing (1), Inappropriate Sensing (3) - no inappropriate shocks,
Discusssion: - In the permanent implantation studies, the subcutaneous ICD successfully and consistently detected and converted VFib that was induced during EP testing. - It also detected and treated 12 episodes of spontaneous VTach that occurred in patients who were in European Clinical Trial - The goal of developing a subcutaneous ICD was to overcome some of the associated with transvenous leads in conventional ICD. - Such device can reduce or eliminate problems like failure to achieve vascular access, intravascular injury, lead failure resulting in difficult extraction and replacement. - Additional benefits includes preservation of venous access for other uses, avoidance of radiation exposure and possible less chances of lead infection.
Discusssion: - These benefits would be especially important for young patients, in whom leads may fail during the decades of therapy. - The need for ICD systems that avoid the use of transvenous leads has been recognized previously. Some physicians have adapted existing technology to treat children with limited venous access. - Epicardial and subcutaneous leads have been used. Other subcutaneous defibrillation systems have been shown to work with an approximate tripling of the energy. - However, earlier systems have not incorporated subcutaneous rhythm detection, but have used transvenous or epicardial sensing electrode for detection.
Discusssion: - These preliminary, early-phase trials show the feasibility of an entirely subcutaneous ICD. - They provide limited information regarding the detection and conversion of VTach in clinical setting, despite detection and termination of VFib at the time of implantation. - These studies can't show whether subcutaneous ICDs are superior to conventional transvenous ICDs. - Initial problems include lead migration, lead dislodgement and inappropriate sensing. The subcutaneous ICD system was adjusted to improve system reliability. - lead dislodgement prevented by anchoring sleeve and new surgical technique. Inappropriate sensing was addressed by software revision, with no incidents in last 3 months.
Discusssion: - The relative benefit of subcutaneous ICDs, as compared with transvenous ICDs, will need to be shown in large, long-term randomized, prospective, multicenter clinical trials. - Limitations (1) Only transient post-shock pacing is available, the subcutaneous ICD can't provide long-term pacing. So, not an alternative to transvenous ICDs when antibradycardia pacing is needed. (2) Subcutaneous ICD not designed to treat patients with VTach < 170 bpm. (3) The lack of capability to provide antitachycardia pacing may be a limitation in patients with frequent, recurrent, monomorphic VTach.
Conclusion: - In small nonrandomized studies, an entirely subcutaneous ICD system successfully and consistently detected and converted episodes of VFib that were induced during EP testing. - It also successfully detected and treated all 12 episodes of spontaneous, sustained VTach.