Phrenic Nerve Injury
Phrenic Nerve Injury
We prospectively enrolled 100 consecutive RF PVI patients who gave written consent for our atrial fibrillation research study that was approved by the Johns Hopkins Institutional Review Board. Patients with drug refractory paroxysmal and persistent AF were enrolled.
Patients underwent RF PVI using a 3-D electroanatomic mapping system, irrigated 4-mm-tip catheter, and integrated ablation system (ThermoCool, Biosense Webster Inc., Diamond Bar, CA, USA) under general anesthesia. PVI with WACA approach was started with the left pulmonary veins, during which neuromuscular blockade was stopped. After confirmation of reversal of neuromuscular blockade with intraprocedure electromyography, high-output (20 mA at 2 milliseconds, EPS320 Micropace EP Inc., Santa Ana, CA, USA) endocardial pacing was performed with the ablation catheter to look for PNC around the wide-area circumferential trajectory for the right superior and inferior pulmonary veins. Pacing was also performed in the carina between the right superior and inferior PVs. If PNC was demonstrated along the anticipated ablation line trajectory or between the PVs, a marker dot was placed at that site in the electroanatomic map. The resulting locus of marker dots was used to indicate the course of the phrenic nerve. If PNC was identified along the anticipated wide-area circumferential ablation line trajectory, the lesion set was modified either toward the atrial side or closer to the vein, depending on the location of PNC and operator's preference. During RF PVI, 30–35 W was delivered at each site along the ablation line.
Clinical characteristics recorded for each patient included age, sex, race, type of AF, body mass index, comorbidities, left ventricular systolic function, renal function, left atrial dimensions, and time spent during the pacing protocol. Left atrial dimension was measured based on preacquired cardiac MRI or CT image. The anteroposterior axis (X) was measured from the center of the posterior wall to the mitral valve plane, the horizontal axis (Y) was measured between the left carina and the right carina and the height (Z) was measured from the center of the left atrial floor to the center of the roof. Occurrence of phrenic nerve injury was assessed with fluoroscopy during the procedure and during physical exam prior to discharge.
Continuous variables were reported as mean ± standard deviation and group differences determined by a 2-sample t-test (2-sided with a P ≤ 0.05 considered statistically significant). Categorical variables were summarized as percentages.
Methods
Patient Population
We prospectively enrolled 100 consecutive RF PVI patients who gave written consent for our atrial fibrillation research study that was approved by the Johns Hopkins Institutional Review Board. Patients with drug refractory paroxysmal and persistent AF were enrolled.
Ablation Procedure and the Pacing Protocol
Patients underwent RF PVI using a 3-D electroanatomic mapping system, irrigated 4-mm-tip catheter, and integrated ablation system (ThermoCool, Biosense Webster Inc., Diamond Bar, CA, USA) under general anesthesia. PVI with WACA approach was started with the left pulmonary veins, during which neuromuscular blockade was stopped. After confirmation of reversal of neuromuscular blockade with intraprocedure electromyography, high-output (20 mA at 2 milliseconds, EPS320 Micropace EP Inc., Santa Ana, CA, USA) endocardial pacing was performed with the ablation catheter to look for PNC around the wide-area circumferential trajectory for the right superior and inferior pulmonary veins. Pacing was also performed in the carina between the right superior and inferior PVs. If PNC was demonstrated along the anticipated ablation line trajectory or between the PVs, a marker dot was placed at that site in the electroanatomic map. The resulting locus of marker dots was used to indicate the course of the phrenic nerve. If PNC was identified along the anticipated wide-area circumferential ablation line trajectory, the lesion set was modified either toward the atrial side or closer to the vein, depending on the location of PNC and operator's preference. During RF PVI, 30–35 W was delivered at each site along the ablation line.
Data Collection and Assessment of Phrenic Nerve Injury
Clinical characteristics recorded for each patient included age, sex, race, type of AF, body mass index, comorbidities, left ventricular systolic function, renal function, left atrial dimensions, and time spent during the pacing protocol. Left atrial dimension was measured based on preacquired cardiac MRI or CT image. The anteroposterior axis (X) was measured from the center of the posterior wall to the mitral valve plane, the horizontal axis (Y) was measured between the left carina and the right carina and the height (Z) was measured from the center of the left atrial floor to the center of the roof. Occurrence of phrenic nerve injury was assessed with fluoroscopy during the procedure and during physical exam prior to discharge.
Statistical Analysis
Continuous variables were reported as mean ± standard deviation and group differences determined by a 2-sample t-test (2-sided with a P ≤ 0.05 considered statistically significant). Categorical variables were summarized as percentages.
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