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Acta Cardiol 2008; 63(1): 59-63
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Pagina 59
doi: 10.2143/AC.63.1.2025333
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Diagnostic value of stored electrograms in pacemaker patients
Stelios PARASKEVAIDIS, Georgios GIANNAKOULAS, Kostas POLYMEROPOULOS, Vasilis VASSILIKOS, Chrisafios GIRASIS, Stavros HADJIMILTIADES, Georgios PARCHARIDIS First Cardiology Department, Aristotle University of Thessaloniki, AHEPA Hospital, Thessaloniki, Greece. Objective — Stored electrograms (EGMs) are diagnostic tools in modern pacemakers, providing data concerning arrhythmia occurrence and device function. We sought to validate the impact of stored EGMs on diagnosis and verification of arrhythmias presented after pacemaker implantation. Methods and results — We enrolled 71 consecutive patients (mean age 64∞∞±∞∞8∞∞years, 51∞∞men) with a standard indication for pacemaker implantation. The following pacemaker devices were implanted: DDDR∞∞=∞ 57,VDDR∞∞=∞ 5,VVIR∞∞=∞ 9. EGM triggers were atrial tachycardia (AT), non-sustained ventricular tachycardia (NSVT) and ventricular tachycardia (VT). We retrieved and analysed 362 EGMs at 3 and 6∞∞months after implantation. The EGMs were triggered by AT in 260 EGMs (72%), by NSVT in 80 (22%) and by VT in 22 (6%). In total, 243 episodes (67%) confirmed the arrhythmic events, while 119 episodes (33%) were classified as false-positive. They were divided into false-positive AT in 85 EGMs (33%), false-positive NSVT in 28 (35%) and false-positive VT in 6 EGMs (27%). The false-positive AT cases were caused by ventricular far-field sensing from the atrial channel in 34 EGMs (40%) and noise or myopotentials in 51 EGMs (60%). Most of the false-positive VT and NSVT episodes were due to atrial fibrillation or atrial tachycardias in 21 EGMs (62%), while the rest were caused by noise in 11 EGMs (32%) or ventricular T wave oversensing in 2 EGMs (6%). Conclusions — Stored EGMs in pacemaker patients were diagnostic in two thirds of arrhythmic episodes.They are useful tools to diagnose arrhythmias and identify sensing problems, and they contribute to optimal device programming and patient management. Keywords: pacemaker diagnostics – stored electrograms – arrhythmias.
Introduction Evolution of pacemaker technology with improvement of the memory function expanded the diagnostic and therapeutic capabilities1,2. Until recently the interrogation of the device provided real time data concerning pacemaker battery status, lead impedance, intrinsic amplitude, rate histograms and event counters. New-generation pacemakers allow the automatic, periodic measurement and storage with histograms of the battery status, lead impedance, intrinsic amplitude range, pacing threshold and adjustment of the pacing output and sensitivity. An additional important feature is the capability of electrogram (EGM) storage
Address for correspondence: Stelios Paraskevaidis, M.D., 33 G. Gennimata str., Agios Ioannis-Kalamaria, Thessaloniki 55134, Greece. E-mail:
[email protected] Received 26 April 2007; revision accepted for publication 13 September 2007.
with marker annotation and onset recordings for detection and confirmation of arrhythmias3,4. The aim of our study was to evaluate the contribution of stored EGMs on diagnosis and verification of arrhythmias occurring in patients after pacemaker implantation.
Methods We enrolled 71 consecutive patients (mean age 64∞∞±∞ 8∞ years, 51∞∞men) implanted with a pacemaker. The EGM storage was activated before patient discharge and interrogated in each of the programmed post implant visits at 3 and 6∞∞months. At 6∞∞months after implantation 362 EGMs were recorded. The following pacemaker devices were implanted: 57 DDDR (5 biventricular), 5 VDDR, 9 VVIR (Guidant in 55%, Medtronic in 20% and St. Jude in 25% of patients). The indications for pacing were AV block in 38∞∞patients, sick sinus syndrome in 13, carotid sinus
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syndrome in 6, slow atrial fibrillation in 9 and severe chronic heart failure with LBBB in 5∞∞patients. All leads were bipolar. The primary underlying heart disease was coronary artery disease in 45∞∞patients, valvular disease in 5∞∞patients, and dilated cardiomyopathy in 4∞∞patients. In 17∞∞patients no heart disease was established. EGMs triggers were programmed as: atrial tachycardia (AT) defined as 8 beats∞∞>∞∞160∞∞bpm, ventricular tachycardia (VT) defined as 8 beats∞∞>∞ 160∞∞bpm not preceded by an atrial event and atrial rate lower than ventricular rate and non-sustained VT (NSVT) defined as∞∞>∞∞3 consecutive premature ventricular beats. The storage capability of the pacemaker was maximum 40∞∞sec programmed for recording 5 episodes of 8∞∞sec each in a rolling mode with marker annotation and onset recordings. The first 4∞∞sec recorded the onset of the event before the trigger while the last 4∞∞sec recorded the post-trigger EGMs. The EGM storage feature of a pacemaker does not consume energy more than 1.8∞∞days per year of life battery. An event was classified as confirmed when it fulfilled the detection criteria and false positive when the recorded event was different from the programmed trigger. The sensitivity values were the nominals: mean atrial sensitivity 0.6∞∞±∞∞0.2∞∞mV and mean ventricular sensitivity 2.5∞∞±∞∞0.5∞∞mV, while the mean P wave amplitude at implantation was 1.4∞∞±∞ 0.6∞∞mV and the mean R wave amplitude was 7.7∞∞±∞∞1.6∞∞mV. Interpretation of the recorded EGMs was made by two physicians and if no consensus was reached, the opinion of a third physician was required. The study complied with the Declaration of Helsinki and was approved by the local ethics committees.
Table∞∞1. – Results of the EGM analysis Trigger
Confirmed
AT NSVT VT Total
175 52 16 243
(67%) (65%) (73%) (67%)
False positive 85 28 6 119
(33%) (35%) (27%) (33%)
Total 260 80 22 362
AT: atrial tachycardia, NSVT: non-sustained ventricular tachycardia, VT: ventricular tachycardia.
were managed by antiarrhythmic drugs in 11∞∞patients (31%) and by anticoagulation in 6∞∞patients (17%) according to the thrombotic risk profile of each patient. The efficacy of antiarrhythmic treatment was monitored by the pacemaker, which continued to record new episodes until the next follow-up visits. The false positive cases were managed by reprogramming the sensitivity values and readjustment, if needed, was made at the next visits. History of AT before implantation was found in 10% of patients. A true NSVT was confirmed in 52 episodes (65%) and VT in 16 (73%) (figure 3). Most of the false-positive VT and NSVT episodes were due to atrial fibrillation or atrial tachycardias in 21 EGMs (62%) (figure 4), while the rest were due to noise in 11 EGMs (32%) or ventricular T wave oversensing in 2 EGMs (6%). The true cases of VT were managed by antiarrhythmic drugs in 16∞∞patients (76%), an electrophysiologic study was performed in 15∞∞patients (71%) and an ICD was implanted in 4∞∞patients (19%). The false positive cases were managed by reprogramming the sensitivity values. No patient had a history of VT before implantation.
Discussion Results In a follow-up period of 6∞∞months arrhythmic events occurred in 43∞∞patients (60.5%). We retrieved and analysed 362 EGMs. They were triggered by AT in 260 episodes (72%), by NSVT in 80 (22%) and by VT in 22 EGMs (6%) (table 1). In 243 episodes (67%) the EGMs confirmed the type of triggering event, while the remaining 119 (33%) were classified as falsepositive. The false-positive episodes were AT in 85 EGMs (33%), false-positive NSVT in 28 (35%) and false-positive VT in 6 EGMs (27%) (table 1). Thirtyseven∞∞patients (52%) had confirmed arrhythmic episodes, 15∞∞patients (21%) false-positive and 19∞∞patients (27%) both. True AT episodes were found in 35∞∞patients and true VT episodes in 21∞∞patients. A true AT was documented in 175 episodes (67%) (figure 1). The false-positive AT episodes were due to ventricular far-field sensing by the atrial channel in 34 EGMs (40%), to noise (figure 2) or myopotentials in 51 EGMs (60%). The true cases of AT, if frequent,
Modern pacemakers are sophisticated devices with many therapeutic and diagnostic functions. Pacemaker diagnostics (including histograms, marker channels, event counters and stored EGMs) provide unique information about device function and can be used to monitor arrhythmias1-2. Diagnostically, one important feature used in ICDs, the EGM storage, has now been incorporated in pacemakers, after improvement in memory capacity. The EGM storage is particularly helpful for arrhythmia detection and confirmation, allowing verification of diagnostic data, thereby elucidating possible detection problems or incorrect classifications of sensed events3-6. Charles et al. reported their experience from 73∞∞patients with a DDD pacemaker and 192∞∞stored EGMs7. The trigger for storage was Automatic Mode Switch (AMS) episode in 28%, sustained VT in 14% and non-sustained VT in 58%. An arrhythmia was confirmed in 31% of the stored EGMs, not confirmed in 47% and 22% were classified as false-positive due to inappropriate sensing.
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Fig.∞∞1. – True atrial tachycardia. Stored electograms were triggered by atrial tachycardia.
Fig.∞∞2. – False positive atrial tachycardia. Stored electograms were triggered by atrial noise.
The EGMs combined with marker annotations and onset recording before detection criteria were fulfilled, confirm the arrhythmic events and the optimal pacemaker programming and function. Marker annotation provides information about sensed or paced events, activation of algorithms and sensors. Nowak et al. reported that in 65 DDDR pacemaker recipients, 319 EGMs were recorded in a one-month period5. Diagnostic EGMs without markers/annotations amounted to 114 (35.7%) while 315 (98.8%) EGMs were diagnostic with the use of marker/onset recordings. Pacemaker patients often have tachyarrhythmias not always detected before implantation. It is esti-
mated that 10-45% of patients with sick sinus syndrome develop atrial tachycardias8,9. In the majority of our patients no tachyarrhythmia was present before implantation. The storage of these episodes by the pacemaker helps the physician to diagnose and initiate, where needed, antiarrhythmic medication and/or anticoagulation according to the patient’s risk profile. It facilitates monitoring of the arrhythmic burden and the efficacy of antiarrhythmic treatment. In our study we observed 33% false positive AT episodes. These cases were mainly due to ventricular farfield sensing by the atrial channel and to myopotentials
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Fig.∞∞3. – True ventricular tachycardia. Stored electograms show an episode of nonsustained ventricular tachycardia with ventriculoatrial dissociation.
Fig.∞∞4. – False positive ventricular tachycardia. Stored electograms were triggered by rapid atrial tachycardia.
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or noise. This occurred despite the exclusive use of bipolar atrial leads. Previous studies demonstrated that false positive AT episodes occurred in a range of 33-65%5,10. In these studies the reasons for the higher false positive results were ventricular far-field sensing, myopotentials, sinus tachycardia, interference and premature atrial events. Detection of AT episodes depends on the atrial rate, length of atrial blanking period, refractory periods and programmed atrial sensitivity6. In our cases, the majority of ventricular far-field sensing was resolved by increasing the atrial sensitivity value, thus providing an adequate sensing threshold safety margin. The prognostic role of the detection and confirmation of atrial tachycardias is crucial. Glotzer et al. in the MOST trial studied 312 pacemaker patients with sinus node dysfunction and atrial high rate episodes∞∞>∞∞220∞∞bpm, lasting∞∞>∞∞5∞∞min detected by the devices11. They reported that the detection of atrial high rate episodes was an independent predictor of death, stroke or atrial fibrillation over a follow-up period of 27∞∞months. The patients with atrial high rate episodes were more than twice as likely to die or to have a stroke and six times as likely to develop atrial fibrillation. In our study the diagnosis of VT or NSVT was confirmed in 67% of episodes. These results are in contrast with the study of Nowak et al. who demonstrated that VT was confirmed only in 18%, probably due to the exclusive use of bipolar ventricular leads in the present study6. In their study unipolar ventricular leads were implanted in 21% of patients and 74% of false positive VT episodes were recorded in patients with unipolar leads. Similarly Defaye et al. reported that a false positive VT occurred in 73% of patients with unipolar leads and only in 17% with bipolar leads12. Further evaluation of our true VT cases resulted in treatment modification, including initiation of amiodarone, electrophysiologic study or ICD implantation. The false positive cases were due to atrial fibrillation or atrial tachycardias in 62%, to noise in 32% or ventricular T wave oversensing in 6% and were managed mainly by reprogramming the sensitivity values as we did in the AT cases. The detection of asymptomatic non-sustained and sustained VTs, in patients with decreased ejection fraction is of clinical importance, as it may identify candidates for ICD implantation. In the future, improvement in pacemaker memory will allow greater storage capabilities of frequent and long-lasting arrhythmic events, regarding date, time, duration and number of the episodes.
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Conclusion The new pacemakers with stored EGMs are significant tools to detect and confirm arrhythmias, to evaluate pacemaker and lead function and to identify sensing problems. They contribute critically to optimal device programming and the patient’s medical management.
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