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Notes: Transvenous Cryoablation for SVT. Introduction: Radiofrequency (RF) catheter ablation currently is used for treatment of cardiac arrhythmias. Although the success rate is high for almost all supraventricular tachycardias (SVT), this technique has some drawbacks, especially when pulmonary veins (PV) are targeted for treatment of atrial fibrillation (AF). Additionally, new techniques for isolation of the PVs have the drawback that they can be used only for PV isolation and not for routine treatment of other SVTs. The aim of this study was to report on the safety and efficacy of a new cryoablation system for treatment of all SVTs. Methods and Results: Forty-nine patients with SVT (38 men; age 48 years, range 23–76) were enrolled in the study. Five patients were withdrawn from the study before they underwent cryoablation. The remaining 44 patients were treated with cryoablation (22 AF, 15 atrial flutter, 3 accessory pathway, 2 AV nodal reentrant tachycardia, 1 AV junction ablation for permanent AF, 1 atrial tachycardia). Cryoablation was performed with the CryoCorTM cryoablation system, which uses a precooling system and N2O as a refrigerant. The number of freezes applied varied according to the index arrhythmia treated. Successful isolation of PVs was performed in 20 of (96%) 21 AF patients and 53 of 55 veins. The overall acute success was 98% (43/44). Fifty-three PVs were isolated (2.5/patient). The success rate was 100% (23/23) for right-sided procedures. The average and nadir temperatures reached in right-sided and left-sided procedures were −77°C and −80°C and −75°C and −78°C, respectively. No acute PV stenosis was seen. Conclusion: This novel cryoablation system appears to be safe and can successfully treat different types of SVTs, including AF. Isolation of PVs is possible without producing stenosis. Despite the high blood flow in the right atrial isthmus and PVs, bidirectional conduction block can be achieved.

Notes: Heterogeneous Changes in Atrial Electrophysiologic Properties. Introduction: The regional changes in atrial elettrophysiologic properties related to atrial fibrillation (AF) in patients with paroxysmal AF (PAF) and chronic AF (CAF) remain unclear. The purpose of this study was to investigate the regional changes in atrial electrophysiology in patients with AF. Methods and Results: We evaluated the atrial electrophysiology at different sites (high right atrium, low right atrium [LRAJ, and distal coronary sinus [DCS]) in 11 patients with CAF, 8 patients with PAF, and 10 controls. Patients with CAF had significantly prolonged interatrial conduction and corrected sinus node recovery time, and shortened atrial effective refractory period (ERP) with loss of rate-related adaptation in the DCS, hut had paradoxic prolongation of atrial ERP in the LRA, as compared with patients with PAF and the controls. As a result, the spatial distribution of atrial ERP that was observed in the controls and in patients with PAF was reversed in patients with CAF, without an increase in the dispersion of atrial refractoriness. Patients with PAF showed intermediate changes in atrial conduction times and atrial refractoriness as compared with patients with CAF and controls. Conclusion: There was a regional heterogeneity on the changes of atrial electrophysiology in different parts of the atrium, and the “normal” spatial distribution of atrial refractoriness was reversed in patients with CAF. The electrophysiologic changes observed in patients with PAF appear to behave as if in transition from the control state to CAF, suggesting progressive changes in atrial electropbysiologic properties.

Notes: Electrode Length for Atrial Defibrillation. Introduction: Catheter-based electrodes have been used previously to terminate episodes of atrial fibrillation in animals and man. Typically, these electrodes span 6 to 7 cm, and lowest energy requirements are achieved when these electrodes are positioned in the distal coronary sinus and in the right atrium. The purpose of this study was to evaluate the use of longer electrode lengths for atrial defibrillation. Methods and Results: In 15 patients, two decapolar catheters were inserted, one into the distal coronary sinus and one in the right atrium. To provide longer electrodes lengths, a third catheter was inserted and alternated positioned in the right atrium or coronary sinus. A 6-cm electrode span was obtained by using the distal 8 rings on the coronary sinus catheter or 8 consecutive electrodes on the right atrial catheter and increased from 6 to 11 cm by connecting consecutive, nonoverlapping rings of the third catheter with the 10 rings of the initial right atrial or coronary sinus catheter. Atrial defibrillation thresholds were determined twice, in a randomized order, in each patient for each of the three combinations of electrode lengths. All 15 patients could he successfully converted to sinus rhythm without complications; however, one patient could be converted reproducibly with only 2 of the 3 electrode combinations. Mean thresholds were 306 ± 102 V, 5.9 ± 4.0 J for the 6 cm/6 cm electrode length combination with an impedance of 72 ± 18 ω. For the electrode combination using the 11-cm electrode in the right atrium, the defibrillation threshold was 296 ± 107 V, 5.8 ± 3.9 J with an impedance of 61 ± 17 ω and was 294 ± 91 V, 5.6 ± 3.6 J with an impedance of 55 ± 11 ω for the 11-cm electrode in the coronary sinus. There were no significant differences in defibrillation voltage or energy (P 〉 0.05) associated with the longer electrode lengths; however, the longer electrode lengths did significantly lower shock impedance (P 〈 0.05). Conclusion: The use of longer electrodes, when using the right atrium to coronary sinus shock vector, does not lower the defibrillation requirements for restoration of sinus rhythm.

Notes: The dose-response relationship for successful defibrillation has been determined in man for the ventricle but not for the atrium. The purpose of this study was to determine the dose-response relationship for internal atrial defibrillation in humans. Seventy-seven consecutive patients underwent internal atrial defibrillation for acute (n = 14) or chronic AF (n = 63). Shocks were delivered in 40-V increments between electrodes positioned in the coronary sinus and the right atrium until successful conversion or a maximum of 400 V was reached. The shock strength versus success of shock data were subjected to a Kaplan-Meier survival analysis combined with a nonparametric probability analysis to arrive at the dose-response relationship. Using this relationship, comparisons were made between acute and chronic AF and clinical relevant conversion percentages (20, 50, 80 and 95%) were estimated and were compared with the conventional mean threshold. There were significant dose-response relationships in both patients groups (P 〈 0.05). The Kaplan-Meier analysis comparing patients with chronic and acute AF showed significant differences in their dose-response relationships (P 〈 0.001). The estimated shock intensity for 95% conversion in patients with acute and chronic AF was 279 V (2.9 J) and 433 V (6.6 J), respectively (P 〈 0.001). The conventional mean defibrillation threshold in patients with acute (192 ± 15 V. 1.4 ± 0.2 J) and chronic AF (343 ± 8 V, 4.4 ± 0.2 J) predicted the 60% and 45% chance of successful conversion, respectively. In conclusion, this study demonstrates that single shock conversion data can be used to determine a dose-response relationship, which can be used to estimate the shock intensity required for specific successful atrial defibrillation efficacy and to compare different clinical factors that affect defibrillation efficacy. (PACE 2003; 26:1249–1253)

Notes: The aim of the study was to evaluate the effect of preshock atrial pacing on the atrial defibrillation threshold (DFT) during internal cardioversion of AF. The implantable atrial defibrillator has been added to the therapeutic options for patients with recurrent episodes of persistent AF. Although the device is efficient in restoring sinus rhythm, patient discomfort is a limitation. Methods that lower the ADFT are needed. Eleven patients with AF underwent internal cardioversion. In a randomized, crossover design, ADFT testing was performed, applying a step-up protocol starting at 100 V. Rapid atrial pacing was performed with a right atrial catheter for 20 seconds at 90% of the average cycle length of the fibrillatory waves and was immediately followed by a biphasic defibrillation shock. At each energy level, pacing + shock was compared to shock only, until the level at which sinus rhythm was restored by both modes. The step-up protocol was thereafter repeated using the inverse sequence of the two modes. A total of 19 ADFTs were obtained. For 10 the ADFT was lower with pacing + shock, in 4 equal and in 5 higher, than with shock only. The ADFT (mean ± SD) with pacing + shock was 260 ± 84 V (3.4 ± 2.9 J) and did not differ from shock only: 268 ± 85 V (3.8 ± 3.0 J) (P 〉 0.05) . The coefficient of variation and the coefficient of reproducibility for pacing + shock was 16% and 60 V, respectively, and for shock only 17% and 61 V. Rapid atrial pacing did not influence the internal ADFT in AF. The randomized, crossover protocol used was reproducible between different modes, and seems useful when testing the impact of different interventions on the ADFT. (PACE 2003; 26[Pt. I]:1461–1466)

Notes: TSE, H.-F., et al.: Effect of Coexisting Cardiovascular Disease on the Long-Term Efficacy and Safety of the Implantable Atrial Defibrillator. The long-term efficacy and safety of implantable atrial defibrillator (IAD) therapy in patients with AF and cardiovascular disease is unclear. The aim of this study was to evaluate the efficacy and safety of IAD therapy in patients with and without coexisting cardiovascular disease. In 115 patients implanted with an IAD, 85 patients had cardiovascular disease: 41 (48%) patients had 1 cardiovascular abnormality, 29 (35%) patients had 2, 13 (15%) patients had 3, and 2 (2%) patients had 4 different cardiovascular abnormalities. The device was programmed into a rhythm monitoring mode for the first 3-month postimplant period. All defibrillation therapy was performed under physician supervision to monitor safety and efficacy. After this initial monitoring period, patients were allowed to activate their device away from the hospital or clinic. A total of 357 spontaneous AF episodes occurred in 83 (72%) patients during observed operation and the mean shock efficacy was 93.5 ± 20.3% (lower 95% confidence interval [CI] 89.8%). As of the last follow-up, 58 (55%) patients had transition to receive nonphysician observed therapy. Forty-two (72%) patients had experienced 332 episodes of AF for which they had received device therapy away from the hospital/clinic (mean shock efficacy 90.5 ± 39.7%). The presence of hypertension, valvular heart disease, and ischemic heart disease did not affect the shock efficacy of the IAD during physician observed and nonobserved therapy (P 〉 0.05). However, the presence of congestive heart failure was associated with a lower clinical efficacy during observed and nonobserved therapy (P 〈 0.05). Overall, 5,262 shocks have been delivered with the IAD without any episode of proarrhythmia. The observed proarrhythmic risk was 0%, with an estimated maximum proarrhythmic risk of 0.06% per shock (95% upper CI). A stand-alone IAD appears to be safe in the presence of cardiovascular disease. The lower clinical efficacy for AF associated with congestive heart failure might be related to a higher rate of early reinitiation of AF after defibrillation.

Notes: The atrial vulnerable periods (A VP)for shock induction of atrial fibrillation (AF) in humans have not been clearly defined. Furthermore, the safety and efficacy of using low energy biatrial shock delivered transvenously for AF induction are unknown. We tested the safety and efficacy of using very low energy biatrial shocks, delivered between the right atrium and the coronary sinus for AF induction and used this technique to characterize the A VP in nine controls and nine patients with AF. Thirty-volt and 60-V 3/3-ms biphasic shocks were delivered, starting from 50 ms before the atrial effective refractory period with 20-ms increments until the end of the QRS interval to determine the AVP front, AVP end, and the AVP duration. Successful AF induction could be achieved in eight (89%) of the nine controls and in nine (100%) of the nine patients with AF without any complication. In patients with AF, the AVP front started significantly earlier within the QRS complex, and the AVP duration and the AVP duration/QRS percent ratios were also significantly greater as compared to controls. Furthermore, a higher induction shock energy in patients with AF was associated with an increase in AF inducibility and significantly increased the AVP duration and A VP duration/QRS percent ratio as compared to the controls. This study demonstrated the safe and efficacy of delivering a very low energy biatrial shock during the AVP within the R wave for AF induction. The characteristics of A VP in patients with AF were significantly different from normal subjects.

Notes: Prior to implantation of an atrial defibrillator, its effectiveness should be tested in each patient. A new catheter design for temporary use with electrodes for atrial defibrillation, electrogram sensing, and pacing was tested in this study. Atrial defibrillation thresholds defined using this temporary catheter were compared to the ones defined by catheters intended for chronic use with an implantable atrial defibrillator. Atrial defibrillation threshold was determined in six sheep using both types of catheters. Each animal was subjected to studies on 2 consecutive days. On the first day, shocks were applied between two of the temporary catheters. On the following day, permanent leads were inserted and atrial defibrillation threshold was redetermined. In both cases, defibrillation electrodes were positioned in the same heart location with one electrode in the distal coronary sinus and the second electrode in the right atrium. Atrial defibrillation threshold was obtained using 10 V increments or decrements to determine the lowest shock intensity needed to defibrillate the atria. Threshold was defined as the shock intensity at which 20 shock percent success was at or between 15 % and 85%. Statistical analysis showed no significant difference (P 〈 0.05) between atrial defibrillation threshold energy (0.53 J vs 0.55 J), voltage (122 V vs 120 V) or current (2.2 A vs 2.6 A) measured with the temporary catheters and the permanent leads, respectively. These data indicate that temporary catheters can be used for efficacy testing prior to implant of an atrial defibrillator, and that they predict atrial defibrillation threshold adequately for chronic leads.

Notes: We investigated in sheep, non-thoracotomy extraction of leads which had been chronically implanted in the right atrium (RA), coronary sinus/great cardiac vein (CS / GCV) and right ventricle (RV) for atrial implantable defibrillation. Clinical success of extraction as well as gross and histologic findings in the heart are reported. Six of nine sheep had successful extractions. The major complication was laceration of the wall of the great coronary vein with hemorrhage into the pericardial space and cardiac tamponade. Tissue damage included several reversible changes: intra-tissue hemorrhage, thrombosis in the veins, and some necrosis of fat, vascular wall and myocardium. Myocyte necrosis was estimated as 0.03 to 0.3 grams of tissue. Osseous and cartilaginous metaplasia was more common around the RA lead than the CS/GCV lead. In cases where the lead must be removed, removal from the venous insertion site using lead extraction equipment should only be attempted with surgical back-up for emergency thora-cotomy to control hemorrhage in the event of vessel laceration. Safer explantation of these leads from the vein entry site will require the development of new extraction procedures.

Notes: Pericardial Sac as Amiodarone Reservoir. Introduction: We investigated whether amiodarone delivered into the pericardial sac exerted an effect on atrial and ventricular refractoriness, impulse generation, and conduction and on induced atrial fibrillation. Methods and Results: All animals were anesthetized with α-chloralose. After a sternotomy, the pericardium was opened and cradled to produce a “container” of approximately 75 mL. Part 1 experimental animals received amiodarone, 0.5, 1.0, or 5.0 mg/mL, dissolved in 3 mL polysorbate 80 and 5% dextrose in water (D5W) instilled into their pericardial sac for 3-hour intervals. Part II experimental animals received either 1.0 or 5.0 mg/mL of amiodarone. Control dogs received a pericardial solution of 3 mL polysorhate 80 in D5W. Pre- and postinstillation electrophysiologic studies were performed. In part I, the increase in sinus cycle length, 1:1 AV conduction, and effective refractory period (ERP) of atrium, right ventricular (RV) and left ventricular epicardium, and RV endocardium were significantly greater in animals receiving amiodarone compared with controls. Amiodarone concentrations in the tissue samples were highest in the superficial sites of the atria, sinoatrial node, and ventricular epicardial samples and lowest in the interventricular septum. Only trace concentrations of amiodarone and no desethylamiodarone were found in the blood samples. In part II, atrial ERP significantly increased in the animals receiving amiodarone, and the number of episodes of sustained atrial fibrillation that could he induced decreased. Conclusions: Amiodarone instilled into the pericardial sac migrates transmurally to produce significant electrophysiologic effects at superficial sites and appears to suppress electrically induced atrial fibrillation.