Faculty Bibliography

Introduction: The safe use of antitachycardia pacing (ATP) to terminate rapid ventricular tachycardias (VTs) (cycle length 240-320 ms) is predicated on the ability of implantable cardioverter defibrillators (ICDs) to distinguish rapid VT from ventricular fibrillation (VF). We set out to compare the time to device charging following the induction of VF of various ICD multizone detection algorithms for rapid VT/VF discrimination. Methods and Results: Data on the time to device charging following the induction of VF at the time to device implantation were collected on 62 consecutive patients in a nonrandomized prospective cohort fashion. Multizone programming for the Boston Scientific, Medtronic, and St. Jude Medical devices was based on prior clinically validated data. Sixty-two subjects were studied (Boston Scientific = 16, Medtronic = 27, St. Jude Medical = 19) and 124 tests for VF detection were performed (Boston Scientific = 32, Medtronic = 54, St. Jude Medical = 38). Mean time to charging was significantly prolonged in the Boston Scientific group as was the percentage of tests where charge initiation occurred >5 seconds from VF-induction: 4.24, 3.99, and 3.00 seconds and 19%, 4%, and 0% for the Boston Scientific, Medtronic, and St. Jude Medical groups, respectively, P < 0.05. ATP was the first therapy administered in 9.4% of tests in the Boston Scientific group. Conclusion: The Boston Scientific multizone VT/VF discrimination algorithm results in a prolonged time to VF detection, and consequently, prolonged time to appropriate initiation of device charging. Further studies are needed to determine whether prolonged detection times lead to clinically significant events. (PACE 2012; 35:1222-1231).

BACKGROUND: Spinal cord stimulation (SCS) has been shown to modulate atrial electrophysiology and confer protection against ischemia and ventricular arrhythmias in animal models. OBJECTIVE: To determine whether SCS reduces the susceptibility to atrial fibrillation (AF) induced by tachypacing (TP). METHODS: In 21 canines, upper thoracic SCS systems and custom cardiac pacing systems were implanted. Right atrial and left atrial effective refractory periods were measured at baseline and after 15 minutes of SCS. Following recovery in a subset of canines, pacemakers were turned on to induce AF by alternately delivering TP and searching for AF. Canines were randomized to no SCS therapy (CTL) or intermittent SCS therapy on the initiation of TP (EARLY) or after 8 weeks of TP (LATE). AF burden (percent AF relative to total sense time) and AF inducibility (percentage of TP periods resulting in AF) were monitored weekly. After 15 weeks, echocardiography and histology were performed. RESULTS: Effective refractory periods increased by 21 +/- 14 ms (P = .001) in the left atrium and 29 +/- 12 ms (P = .002) in the right atrium after acute SCS. AF burden was reduced for 11 weeks in EARLY compared with CTL (P <.05) animals. AF inducibility remained lower by week 15 in EARLY compared with CTL animals (32% +/- 10% vs 91% +/- 6%; P <.05). AF burden and inducibility were not significantly different between LATE and CTL animals. There were no structural differences among any groups. CONCLUSIONS: SCS prolonged atrial effective refractory periods and reduced AF burden and inducibility in a canine AF model induced by TP. These data suggest that SCS may represent a treatment option for AF.

Background: The Medtronic Sprint Fidelis (Medtronic Inc., Minneapolis, MN, USA) lead family is associated with an unacceptable incidence of premature lead failure. There are limited data on risk factors for lead fracture. We hypothesized that factors leading to potential increased forces on the lead related to device implantation or technique may be associated with premature lead failure. Methods: We reviewed the implant data from our group and identified 176 patients who received active fixation Medtronic Fidelis (Model 6931, single coil and Model 6949, dual coil) leads. Implant data, including age, sex, venous access site, implant side, implant location, and number of venous leads were reviewed. Hospital, pacemaker clinic, and Medtronic registration databases were reviewed for evidence of lead failure, replacement, or abandonment. Data was evaluated in univariate and multivariate regression analyses. Results: Of the 176 leads implanted, 10 (5.7%) were noted to develop malfunction. This presented as inappropriate shocks from sensed noise or elevated impedance measurements. Of the above noted implant features, only right-sided (vs left-sided) implant (hazard ratio [HR] 18.8, 95% confidence intervals [CI] 3.8, 93.3), and subpectoral implant (vs prepectoral; HR 14.31, 95% CI 3.2, 64.0) were predictive of lead failure in maximally adjusted models. Conclusions: We have identified both right-sided implantation and subpectoral generator positioning as factors associated with premature lead malfunction in Fidelis active fixation leads. Clinical decisions regarding patient management should incorporate these findings in regard to lead replacement in high-risk patients. (PACE 2012; 35:659-664).

Introduction: Spinal cord stimulation (SCS) has been shown to modulate atrial electrophysiology and confer protection against ischemia and ventricular arrhythmias in animal models. We hypothesized that SCS would reduce the susceptibility to tachypacing (TP) induced atrial fibrillation (AF). Methods: In 21 canines, an upperthoracicSCS system (EonC Model 3688, Octrode Model 3186, St. Jude Medical, Piano TX) and custom cardiac pacing system (PM, Model 5386 or 2215-36, St. Jude Medical, Sylmar CA) were implanted. Atrial effective refractory periods (ERPs) in the high right atrium (RA) and distal coronary sinus (LA) were measured at baseline and after 15 min of SCS, after which AV nodal ablation was performed. Following recovery in a subset of canines, PM was turned on to create TP induced AF by alternately delivering TP and searching for AF. TP was interrupted by detection of AF and resumed after return to sinus rhythm. Upon initiation of TP, canines were randomized to no SCS therapy (CTL, n=6) or intermittent SCS therapy (SCS-ON, n=4) and followed for 15 weeks. AF burden, defined as the percent of time in AF relative to the total sense time, and AF inducibility, defined as the percent of TP periods resulting in AF induction, were monitored weekly. Data are presented as mean +/- standard error. Results: ERPs were significantly longer after SCS compared to baseline, byan average of21 +/-14ms (p=0.001) in LA and 29+/-12ms (p=0.002) in RA. The AF burden was significantly decreased by 34 percentage points at week 15in SCS-ON compared to CTL (56 +/- 21% vs 90 +/- 12%, p<0.05). AF inducibility was significantly reduced by 60 percentage points at week 15 in SCS-ON compared to CTL (32 +/- 10% vs 91 +/- 6%, p<0.05). Conclusions: SCS prolonged atrial ERPs and reduced AF burden and inducibility in a canine atrial TP induced AF model. These data suggest that SCS therapy may represent a treatment option for AF

BACKGROUND: Transmural lesions are essential for efficacious ablation. There are, however, no accurate means to estimate lesion depth. OBJECTIVE: Explore use of the electrical coupling index (ECI) from the EnSite Contact System as a potential variable for lesion depth estimation. METHODS: Radiofrequency (RF) ablation lesions were created in atria and the thighs of swine using an irrigated RF catheter. Power was 30 W for 20 or 30 seconds intracardiac and 30-50 W for 10-60 seconds for the thigh. Intracardiac, the percentage change in ECI during ablation was compared with transmurality and collateral damage occurrence. For the thigh model, an algorithm estimating lesion depth was derived. Factors included: power, duration, and change in the ECI subcomponents (DeltaECI+) during ablation. The DeltaECI+ algorithm was compared to one using power and duration (PD) alone. RESULTS: Intracardiac, lesions with >/=12% reduction in ECI were more likely to be transmural (92.3% vs. 59.4%, P < 0.001). Twenty-second lesions were less likely to cause collateral damage compared to 30 seconds (33% vs. 70%, P = 0.003), while transmurality was similar. With the thigh model, DeltaECI+ had a better correlation than the PD algorithm (P < 0.01). Accuracy of the DeltaECI+ algorithm was unimproved with inclusion of tip orientation, while PD improved (R(2) = 0.64). DISCUSSION: Change in ECI provides evidence of transmural versus nontransmural swine intracardiac atrial lesions. A lesion depth estimation algorithm using ECI subcomponents is unaffected by tip orientation and is more accurate than using PD alone. CONCLUSION: Use of ECI as a factor in a lesion depth algorithm may provide clinically valuable information regarding the efficacy of intracardiac RF ablation lesions

BACKGROUND: There are little data on the appropriate endpoint for slow pathway ablation that balances acceptable procedural times, recurrence rates, and complication rates. This study compared recurrence rates of three commonly utilized endpoints of slow pathway ablation for atrioventricular nodal reentrant tachycardia (AVNRT). METHODS: We performed a meta-analysis of AVNRT slow pathway ablation cohorts by searching electronic databases, the Internet, and conference proceedings. Inclusion criteria were age >18 years, >20 human subjects per study, primary AVNRT ablation, English language publication, and >1 month of follow-up. Data were analyzed with a fixed-effects model using Comprehensive Meta-Analysis software version 2.2.046 (Biostat, Englewood, NJ, USA). RESULTS: We included 10 studies encompassing 1,204 patients with a mean age of 41-53 years. Endpoints were complete slow pathway ablation, residual jump only, and single remaining echo beat. Pooled estimates revealed 28 of 641 patients (4.4%) with complete slow pathway ablation, 13 of 192 patients (6.8%) with a residual jump only, and 24 of 371 patients (6.5%) with one echo had recurrences. With uniform isoproterenol use after ablation, there was no significant difference in recurrence rates among the endpoints. However, when isoproterenol was utilized after ablation only if needed to induce AVNRT before ablation, a significantly higher recurrence rate occurred in patients with a residual jump (P = 0.002), a single echo (P = 0.003), or the combined group of a residual jump and/or one echo (P = 0.001). CONCLUSIONS: Isoproterenol should be used routinely after slow pathway modification, when a residual jump and/or single echo remain

Introduction: Spinal cord stimulation (SCS) has been shown to modulate atrial electrophysiology and confer protection against ischemia and ventricular arrhythmias. We hypothesized that SCS may reduce susceptibility to tachypacing (TP) induced atrial fibrillation (AF). Methods: Spinal cord leads (Octrode, St. Jude Medical) were implanted in the upper thoracic spine (T1-T5) of canines and connected to pulse generators (EonC, St. Jude Medical). The AV node was ablated and atrial effective refractory period (AERP) was measured at baseline and with SCS (n=10). In separate animals the AV node was ablated and endocardial RA and RV pacing leads were connected to dual chamber pacemakers for ambulatory AF induction. Custom firmware provided continuous 30s periods of atrial TP followed by 6s sense windows. TP was interrupted by detection of AF (atrial rate >250 bpm) and resumed upon return to sinus rhythm. AF Index was defined as the fraction of time the animal did not receive TP relative to the total allowable TP time. The effect of SCS delivered intermittently for 6 hr/day (SCS ON; n=3) on AF index was followed for 8 weeks and compared to control (SCS OFF; n=3). Results: Right (p=0.002) and left (p=0.009) AERP were significantly longer during SCS (168+/-15.1, 168+/-14.8 ms) compared to baseline (130+/-8.7, 152+/-10.3 ms). AF Index was significantly decreased in the SCS ON compared to SCS OFF (p<0.0001). AF Index was >70% in the SCS OFF group and <5% in the SCS ON animals starting at week 3 (Figure). Conclusions: These data demonstrate that SCS prolongs AERP and prevents TP-induced AE (Graph presented)