Para-Hisian Pacing During Sinus Rhythm: Establishing Threshold Values to Distinguish Nodal From Septal Pathway Conduction.

OBJECTIVES: This study sought to identify minimum threshold values below which conduction over the atrioventricular (AV) node would be unexpected. BACKGROUND: Para-Hisian pacing is used to evaluate for the presence of a septal accessory pathway (AP); however, threshold values to differentiate nodal from AP conduction are unknown. METHODS: The authors performed high- and low-output para-Hisian pacing during sinus rhythm to capture the His and para-Hisian ventricular myocardium (H+V) and para-Hisian ventricular myocardium (V) alone, respectively. The change in stimulation (stim)-to-atrial electrogram interval after loss of His bundle capture in patients with (AP+) and without (AP-) a septal AP was evaluated. Stim-to-proximal coronary sinus (PCS) and stim-to-high right atrium (HRA) intervals were measured and within-patient differences (△) for V and H+V capture were calculated. RESULTS: A total of 23 AP+ and 45 AP- patients were evaluated. The difference in stimulus to earliest atrial signal in the high right atrial catheter seen with the loss of His bundle capture (△-stim-HRA) (21 ms; interquartile range [IQR]: 3 to 43 ms vs. 64 ms; IQR: 56 to 73 ms; p < 0.001) and difference in stimulus to earliest atrial signal in the proximal coronary sinus catheter seen with the loss of His Bundle capture (△-stim-PCS) (11 ms; IQR: 0 to 30 ms vs. 61 ms; IQR: 52 to 72 ms; p < 0.001) were shorter in AP+ patients. The shortest △-stim-PCS and △-stim-HRA in AP- patients were 37 ms and 32 ms, respectively, whereas the longest corresponding intervals in AP+ patients were 51 ms and 75 ms, respectively. CONCLUSIONS: A △-stim-PCS <37 ms or △-stim-HRA <32 ms confirmed the presence of a septal AP, whereas a value >51 ms for △-stim-PCS or >75 ms for △-stim-HRA excluded it. Alternatively, the minimum △-stim-PCS with loss of His capture compatible with AV nodal conduction in isolation was 37 ms, and a △-stim-PCS >51 ms effectively ruled out the presence of a septal AP.

Prevention of venous thrombosis after electrophysiology procedures: a survey of national practice.

PURPOSE: Femoral venous access is required for most electrophysiology procedures. Limited data are available regarding post-procedure venous thromboembolism (VTE), specifically deep vein thrombosis (DVT) and pulmonary embolism (PE). Potential preventative strategies are unclear. We aimed to survey Canadian centers regarding incidence of VTE and strategies for prevention of VTE after procedures that do not require post-procedure anticoagulation. METHODS: An online survey was distributed to electrophysiologists representing major Canadian EP centers. Participants responded regarding procedural volume, incidence of VTE post-procedure, and their practice regarding pharmacological and non-pharmacological peri-procedural VTE prophylaxis. RESULTS: The survey included 17 centers that performed a total of 6062 procedures in 2016. Ten patients (0.16%) had VTE (including 9 DVTs and 6 PEs) after diagnostic electrophysiology studies and right-sided ablation procedures excluding atrial flutter. Five centers (41.6%) administered systemic intravenous heparin during both diagnostic electrophysiology studies and right-sided ablation procedures. For patients taking oral anticoagulants, 10 centers (58.8%) suspend therapy prior to the procedure. Two centers (11.8%) routinely prescribed post-procedure pharmacologic prophylaxis for VTE. Four centers (23.5%) used compression dressings post-procedure and all prescribed bed rest for a maximum of 6 h. Of the variables collected in the survey, none were found to be predictive of VTE. CONCLUSIONS: VTE is not a common complication of EP procedures. There is significant variability in the strategies used to prevent VTE events. Future research is required to evaluate strategies to reduce the risk of VTE that may be incorporated into EP practice guidelines.

Feasibility of extravascular pacing with a novel substernal electrode configuration: The Substernal Pacing Acute Clinical Evaluation study.

BACKGROUND: Subcutaneous implantable cardioverter-defibrillators provide an alternative to transvenous defibrillation but require higher shock outputs and offer no antitachycardia pacing. The Substernal Pacing Acute Clinical Evaluation (SPACE) study evaluated the feasibility of pacing from an extravascular substernal location. OBJECTIVES: The primary purpose of the SPACE study was to characterize pacing from the substernal space. Secondary objectives included evaluating extracardiac stimulation and recording electrograms. METHODS: The SPACE study prospectively evaluated the feasibility of pacing with a commercially available electrophysiology catheter acutely implanted in the substernal space via minimally invasive subxiphoid access. Pacing data were collected in ≥7 vectors using constant current stimulation up to 20 mA and pulse width up to 10 ms. RESULTS: Catheter placement was successful in all 26 patients who underwent the procedure, with a mean placement time of 11.7 ± 10.1 minutes. Eighteen patients (69%) had successful ventricular capture in ≥1 tested vector. The mean pacing threshold at a pulse width of 10 ms was 7.3 ± 4.2 mA across all vectors (5.8 ± 4.4 V). Failed capture was generally associated with suboptimal catheter placement or presumed air ingression. A low level of extracardiac stimulation was observed in 1 patient. The mean R-wave amplitude ranged from 2.98 to 4.11 mV in the unipolar configuration and from 0.83 to 3.95 mV in the bipolar configuration. CONCLUSION: The data from the SPACE study demonstrate that pacing is feasible from the extravascular substernal location. A substernal electrode configuration has the potential to provide pacing in a future extravascular device without need for intracardiac hardware placement.

Voltage-guided ablation technique for cavotricuspid isthmus-dependent atrial flutter: refining the continuous line.

Ablation of the cavotricuspid isthmus has become first-line therapy for "isthmus-dependent" atrial flutter. The goal of ablation is to produce bidirectional cavotricuspid isthmus block. Traditionally, this has been obtained by creation of a complete ablation line across the isthmus from the ventricular end to the inferior vena cava. This article describes an alternative method used in our laboratory. There is substantial evidence that conduction across the isthmus occurs preferentially over discrete separate bundles of tissue. Consequently, voltage-guided ablation targeting only these bundles with large amplitude atrial electrograms results in a highly efficient alternate method for the interruption of conduction across the cavotricuspid isthmus. Understanding the bundle structure of conduction over the isthmus facilitates more flexible approaches to its ablation and targeting maximum voltages in our hands has resulted in reduction of ablation time and fewer recurrences.

Tachycardia induction with ventricular extrastimuli differentiates atypical atrioventricular nodal reentrant tachycardia from orthodromic reciprocating tachycardia.

BACKGROUND: Differentiating atypical atrioventricular nodal reentrant tachycardia (AVNRT) from septal orthodromic reentrant tachycardia (ORT(Septal)) is challenging in nonsustained tachycardia. When sustained, the postpacing interval minus tachycardia cycle length following entrainment (PPI(Entrainment) - TCL) and stimulation to atrial interval minus ventriculoatrial interval (Stim-A(Entrainment) - VA) are utilized. OBJECTIVE: We hypothesized that the first tachycardia cycle after tachycardia induction with right ventricular apical extrastimulation would yield comparable information to entrainment, precluding the need for sustained tachycardia. METHODS: Twenty-four patients with AVNRT (age 47 ± 18 years), 19 with ORT(Septal) (age 42 ± 17 years), and 15 with ORT over a left lateral accessory pathway (ORT(Left)) (age 41 ± 16 years) were included. The ventricular extrastimulus to atrial depolarization at tachycardia initiation (Stim-A(Initiation)) and tachycardia VA interval were measured to establish the Stim-A(Initiation) minus VA interval (Stim-A(Initiation) - VA). The ventricular extrastimulus to the subsequent right ventricular apical depolarization (postpacing interval at initiation, PPI(Initiation)) was utilized to obtain the PPI(Initiation) minus TCL (PPI(Initiation) - TCL). The AH interval associated with the PPI(Initiation) minus the AH in tachycardia was utilized to establish a corrected PPI(Initiation) minus TCL (cPPI(Initiation) - TCL). RESULTS: The intervals after tachycardia initiation were longer for AVNRT than for ORT: mean PPI(Initiation) - TCL (193 ± 44 vs 91 ± 73; P <.001), cPPI(Initiation) - TCL (174 ± 44 ms vs 88 ± 50 ms; P <.001), and Stim-A(Initiation) - VA (161 ± 45 ms vs 69 ± 53 ms; P <.001). The correlation coefficient for Stim-A(Initiation) minus VA against Stim-A(Entrainment) minus VA was 0.79 and for cPPI(Initiation) minus TCL against PPI(Entrainment) minus TCL was 0.71. cPPI(Initiation) minus TCL <115 ms or Stim-A(Initiation) - VA <85 ms was observed only in ORT. The converse was observed in AVNRT but also in ORT(Septal) over decremental accessory pathways and ORT(Left). CONCLUSION: Stim-A(Initiation) - VA < 85 ms or cPPI(Initiation) - TCL < 115 ms excludes AVNRT.

Entrainment for distinguishing atypical atrioventricular node reentrant tachycardia from atrioventricular reentrant tachycardia over septal accessory pathways with long-RP [corrected] tachycardia.

BACKGROUND: The response to right ventricular (RV) entrainment is useful to distinguish atypical AV node reentrant tachycardia from AV reentrant tachycardia using a septal accessory pathway. Whether entrainment can differentiate between AV node reentrant tachycardia and AV reentrant tachycardia in patients with long-RP tachycardia has not been systematically validated. METHODS AND RESULTS: Twenty-four patients with concealed septal accessory pathways who had an electrophysiology study between January 1, 2000, and January 1, 2010, were included (age, 38 ± 17 years; men, 17). Entrainment was performed from the RV apex pacing at cycle length 20 to 40 ms shorter than tachycardia cycle length (TCL). The mean TCL was 390 ± 80 ms, the mean AH interval during tachycardia was 151 ± 57 ms, and the mean ventriculoatrial (VA) time was 182 ± 103 ms. Twelve patients had typical accessory pathways (VA/TCL <40%), and 12 had slowly conducting accessory pathways (VA/TCL ≥ 40%). In all patients with typical accessory pathways, the postpacing interval minus the TCL (PPI-TCL) was <115 ms and the difference in the VA interval during pacing and tachycardia (StimA-VA) was <85 ms. On the other hand, in 6 of the 12 patients in the slowly conducting group, the PPI-TCL was >115 ms, and the StimA-VA was > 85 ms. CONCLUSIONS: Slowly conducting accessory pathways frequently yield RV entrainment criteria traditionally attributable to AV node reentry. Distinguishing AV node reentry from AV reentry in patients with long-RP tachycardia requires other criteria.

Determination of inadvertent atrial capture during para-Hisian pacing.

BACKGROUND: Inadvertent capture of the atrium will lead to spurious results during para-Hisian pacing. We sought to establish whether the stimulation-to-atrial electrogram interval at the proximal coronary sinus (stim-PCS) or high right atrium (stim-HRA) could signal inadvertent atrial capture. METHODS AND RESULTS: Para-Hisian pacing with and without intentional atrial capture was performed in 31 patients. Stim-HRA and stim-PCS intervals were measured with atrial capture, His plus para-Hisian ventricular (H+V) capture, and para-Hisian ventricular (V) capture alone. The mean stim-HRA interval was significantly shorter with atrial capture (66 ± 18 ms) than with H+V (121 ± 27 ms, P < 0.001) or V capture alone (174 ± 38 ms, P < 0.001). The mean stim-PCS interval was significantly shorter with atrial capture (51 ± 16 ms) than with H+V (92 ± 22 ms, P<0.001) or V capture alone (146 ± 33 ms, P < 0.001). A stim-PCS < 60 ms (stim-HRA < 70 ms) was observed only with atrial capture. A stim-PCS >90 ms (stim-HRA >100 ms) was observed only in the absence of atrial capture. A stim-HRA of < 85 ms was highly specific and stim-PCS of < 85 ms highly sensitive at identifying atrial capture. Stim-HRA intervals of 75 to 97 ms and stim-PCS intervals of 65 to 88 ms were observed with either atrial, His, or para-Hisian ventricular capture without atrial capture. In this overlap zone, all patients demonstrated a stim-PCS or stim-HRA interval prolongation of at least 20 ms when the catheter was advanced to avoid deliberate atrial pacing. The QRS morphology was of limited value in distinguishing atrial capture due to concurrent ventricular or H+V capture, as observed in 20 of 31 (65%) patients. CONCLUSIONS: Stim-PCS and stim-HRA intervals can be used to monitor for inadvertent atrial capture during para-Hisian pacing. A stim-PCS < 60 ms (or stim-HRA < 70 ms) and stim-PCS > 90 ms (or stim-HRA > 100 ms) were observed only with and without atrial capture, respectively, but there was significant overlap between these values. Deliberate atrial capture and loss of capture reliably identifies atrial capture regardless of intervals.

Complete antral encirclement is not required for pulmonary vein isolation.

BACKGROUND: Complete circumferential antral ablation may not be necessary for successful pulmonary vein (PV) isolation in patients with paroxysmal atrial fibrillation (AF). OBJECTIVE: We examined the feasibility of a noncircumferential approach limited to segments of the antra required for PV-atrial conduction. METHODS: During ablation for paroxysmal AF, each PV antrum was divided into six segments, and ablation was sequentially targeted to antral segments with the earliest activity until bidirectional isolation was achieved. Ablation at the ostium was avoided. Patients requiring complete circumferential ablation (circumferential group) were compared with those undergoing incomplete antral ablation (noncircumferential group) with respect to freedom from symptomatic atrial arrhythmia, procedure, and ablation times. RESULTS: Ninety-nine patients underwent ablation with successful isolation of PVs (n = 37 circumferential; n = 62 noncircumferential). There were no significant differences in age, gender, AF duration, or LA size. Procedure time (202 ± 45 vs. 185 ± 47 minutes; P = .06) and ablation time (51 ± 15 vs. 41 ± 14 minutes; P = .004) were shorter in the noncircumferential group. During follow-up (12 ± 6 months), freedom from symptomatic recurrence was 73% in both groups (P = .97), with organized atrial tachycardia being more common in the circumferential group (P = .06). In 22 patients undergoing repeat study, PV reconnection was demonstrated in 82% and 81% of PVs in each group. Reconnection in the noncircumferential group occurred in previously ablated segments in 10 (77%) of 13 cases. CONCLUSIONS: Noncircumferential antral ablation achieves similar success rates with shorter procedure and ablation times than circumferential ablation. Greater attention should be focused on producing permanent lesions rather than on completing antral encirclement after isolation is achieved.

Effect of defibrillation testing on management during implantable cardioverter-defibrillator implantation.

BACKGROUND: Verification of defibrillation efficacy by defibrillation threshold (DFT) testing during implantable cardioverter-defibrillator implantation is the current standard. Generally, defibrillation of ventricular fibrillation at 10 J below the maximum output of a device is felt to establish an adequate safety margin. Nonetheless, DFT testing adds to cost and carries some potential for morbidity, whereas its impact on outcomes in the modern era of defibrillator technology is unclear. We aimed to determine the frequency that DFT testing resulted in a change at device implant and to identify clinical and echocardiographic predictors of the need for DFT testing. METHODS: We reviewed all implantable cardioverter-defibrillators that were implanted at the London Health Sciences Centre (Ontario, Canada) from June 1999 to August 2003 and used multivariate analysis to determine variables associated with DFT test failures and elevated DFT values. When a defibrillation failure was not observed, a lowest energy to defibrillate (LED) was recorded. RESULTS: Among 168 implants, DFT testing was successful with a minimum 10-J safety margin in 152 (90%), whereas the remaining 16 required changes at device implant. In a multivariate analysis, use of amiodarone was independently associated with DFT failure (odds ratio, 4.6; 95% confidence interval, 1.2-17.0). Significantly higher mean DFT/LED values were observed among patients on amiodarone (1.36 J; P = .0041). Those with nonischemic cardiomyopathy had a higher mean DFT/LED compared with those with ischemic cardiomyopathy (1.44 J; P = .028). CONCLUSIONS: Use of amiodarone is associated with a 4-fold increase in risk of DFT failure and subsequent need for changes at implant to achieve a safe threshold. Defibrillation threshold testing appears to be most useful for patients taking amiodarone.