Abstract & Commentary
Synopsis: The incidence of sudden death related to AV junctional ablation is low, but Ozcan et al recommend that in-hospital monitoring for a minimum of 2 days after ablation should be considered for patients with predictors of increased risk.
Source: Ozcan C, et al. J Am Coll Cardiol. 2002;40: 105-110.
This paper details the mayo clinic experience with unexpected sudden death after radiofrequency ablation of atrioventricular (AV) nodal conduction. All patients who underwent radiofrequency ablation of the AV node for paroxysmal or chronic atrial fibrillation (AF) at the Mayo Clinic between July 1990 and December 1998 were included in this series. Sudden death was defined as either witnessed death or death within 1 hour from the time the patient was last seen. The sudden deaths were classified as either likely, possibly, or unlikely to be related to the procedure. If sudden death occurred within 48 hours after the procedure or occurred at any time after the procedure in the presense of known coronary vascular disease, the relationship was defined as likely. Sudden deaths occurring in the interval between 2 days and 3 months after the procedure were defined as possibly related. Deaths that occurred more than 3 months after the procedure were defined as unlikely to be related to the procedure. Data were collected from a centralized data repository that provided complete records of patients who underwent AV node ablation and pacemaker implantation at the Mayo Clinic. AV node ablation was performed using a right-sided approach in 98% and a left-sided approach in 2%. Twenty- four patients (7%) developed recurrent AV conduction after an initial attempt and required a second or third procedure. AV block was eventually achieved in all patients. Patients in AF received a VVIR pacemaker. Patients with paroxysmal AF or those in sinus rhythm at the time of the procedure received a dual chamber pacemaker. Before 1997, the lower pacing rate was programmed at 60 bpm. Since 1997, the lower pacing rate was set at 90 bpm immediately after ablation and decreased by 10 bpm per month to a final setting of 60 bpm.
The study included data from 334 patients. The mean age of patients in the study group was 68 ± 11 years. Nine patients had either sudden death (7) or aborted cardiac arrest after the ablation. In 3 patients, the sudden death was thought to be likely related to the procedure because the event occurred within 48 hours of the procedure in 3 cases, and 1 patient without any cardiovascular disease had sudden death 4 days after the procedure. Sudden death in 3 patients was classified as possibly related to the procedure because it occurred between 2 days and 3 months after the procedure. These 3 patients all had significant cardiovascular disease. Two patients died suddenly at 27 and 43 months after the procedure. Both had underlying structural heart disease, and their deaths were considered to be unlikely to be related to the procedure. Among the patients with sudden death likely or possibly related to the procedure, 6 of the 7 patients had structural heart disease. Ventricular arrhythmia had been noted before the procedure in 4 of the 7 patients. Six of the 7 patients had AF at the time of ablation. Six of the 7 patients had a lower pacing rate programmed at 60 bpm immediately after the ablation, with only 1 having the higher pacing rate. The following were identified as independent predictors for sudden death: diabetes mellitus, New York Heart Association functional class ³ 2, preablation ventricular arrhythmias, valvular heart disease (mitral stenosis, aortic stenosis, aortic regurgitation), and chronic lung disease. Five of the arrests occurred in the hospital during postprocedure monitoring. Ventricular fibrillation was noted in 4 patients and polymorphic ventricular tachycardia in 1 patient. There was no evidence for pacemaker failure or malfunction in any of the patients. Ozcan and colleagues conclude that the incidence of sudden death related to AV junctional ablation is low but recommend that in-hospital monitoring for a minimum of 2 days after ablation should be considered for patients with predictors of increased risk.
Comment by John P. DiMarco, MD, PhD
AV junctional ablation was first performed using direct current shocks. This produced a relatively large lesion and there was a significant early and late morbidity and mortality associated with the procedure. The development of radiofrequency techniques allowed more precise localization and control of the lesion used for elimination of AV node conduction, and it was hoped that this would lower the risk of ventricular arrhythmias after the procedure. This paper from a single center covers a large number of patients who were treated using a uniform approach. Ozcan et al document a low incidence of sudden death or cardiac arrest that was considered to be likely related to the procedure, and these data can be used to formulate practical guidelines.
The mechanisms responsible for sudden death in these patients are uncertain. The late sudden deaths are probably related to the progression of the patient’s underlying disease. There was no evidence in this series of pacemaker failure. Even if the pacemaker failed, most patients who have undergone AV junctional ablation will have an escape rhythm adequate to support life long enough for the patient to get to the hospital. It has recently been thought that bradycardia-dependent arrhythmias due to the sudden change in rate might be responsible. For this reason, most electrophysiologists now pace the heart at a lower rate limit of 80-90 bpm for some period of time after the procedure. It should be noted in this series that only one of the patients with sudden death or cardiac arrest were paced at the higher rate and that this laboratory changed their protocol to the higher lower rate limit several years ago. The single patient after the change in protocol had a cardiac arrest 13 days after the procedure and had significant left ventricular dysfunction before the procedure.
The risk factors identified for sudden death in this trial are important for clinicians. Heart rates during AF are often very difficult to control in patients with progressive valve disease or chronic obstructive lung disease. It seems fully justified to keep these patients in the hospital for more than 24 hours based on these data. The observation that diabetes was an independent predictor for sudden death is intriguing. Whether this is related to repolarization abnormalities or antihyperglycemic agents or whether the diabetes was just a marker for underlying coronary artery disease is uncertain.
I think electrophysiologists should follow the suggestions made by Ozcan et al based on their data. Patients with any of the risk factors identified should be monitored at least 48 hours in the hospital. The pacing rate after the procedure should be higher than was used in the early part of this series. Even if the sudden death rate after AV junctional ablation is low, we must remember to be cautious in managing these patients around the time of the procedure.
Dr. DiMarco is Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville.
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