Near-Fatal Episode of Polymorphic Ventricular Tachycardia Captured on Intracardiac Electrogram in a Single Chamber Pacemaker

In this case study, the authors describe how crucial proper programming of stored intracardiac electrograms can be when trying to associate specific cardiac symptoms or events with a stored record.

Case Study

A 78-year-old female presented at the pacer clinic for a routine follow up of a single chamber pacemaker. The patient has a history of rheumatic heart disease, mitral stenosis, and congestive heart failure, and is an insulin-dependent diabetic. She had a single chamber pacemaker (Victory SR Model 5610, St. Jude Medical St. Paul, MN) implanted in January 2007 prior to AV node ablation for chronic atrial fibrillation and better rate control. She had been asymptomatic post ablation until July 2009.

Her medications include diltiazem, ASA, candesartan, fluoxetine, digoxin, metoprolol, insulin and coumadin.

While visiting her daughter in another state on July 7, 2009, she suffered a seizure. Paramedics were summoned and she regained consciousness by the time the paramedics arrived. She was transported to the hospital, and was admitted and subsequently discharged two days later without a reason being ascertained for her apparent seizure. The pacemaker was not evaluated during this hospital admission.

The patient returned home and on July 28, 2009, she underwent a balloon valvuloplasty for critical mitral stenosis. Her left anterior descending and circumflex arteries were basically normal with an approximately 30% stenosis in the right coronary artery. Left ventriculogram showed apical dyskinesis with an ejection fraction of 50%. Again, the pacemaker was not interrogated during this hospital admission.

She presented to her regular pacer clinic on September 1, 2009 for a routine follow up. R waves were not present at a pacing rate of 30 beats per minute (bpm). Pacing threshold was excellent with capture at 0.5V at 0.5ms pulse width. The pacing impedance was 546Ω. The mode was set to VVIR at a base rate of 60 bpm.

Interrogation of the stored intracardiac electrograms (IEGM) revealed 4 stored events for high ventricular rate. The trigger was set to a rate of 150 bpm with 5 consecutive beats at this rate required to store an electrogram. Of note, the stored electrograms were set to “freeze”, indicating that after 4 episodes were recorded, no more storage of new events would occur.

The patient experienced 3 episodes of nonsustained, monomorphic ventricular tachycardia (VT) at a cycle length of approximately 350ms. Each time the VT was self-limiting, with the longest episode lasting for 17 cycles. On July 7, 2009, the date of her seizure, an episode of polymorphic ventricular tachycardia was recorded (Figure 1). The electrogram storage was set for a duration of 26 seconds. The patient was in VT for a minimum of 14 seconds, after which the episode timed out and was stored. This rhythm broke prior to the arrival of paramedics. This also was the last electrogram that could have been stored given the programmed storage parameters. At this point, the patient was scheduled for an upgrade of her single chamber pacemaker to a single chamber defibrillator. She was not indicated for biventricular support given her Class I CHF status.

Discussion

Pacemaker diagnostics, especially the utilization of stored intracardiac electrograms, can be beneficial in associating specific symptoms or events with a stored record.^1,2 Stored electrograms are a well-known diagnostic tool for cardiac devices that allow for clinicians to detect possible problems. Evaluation of pacemaker diagnostics has shown upwards of 67% detection of ventricular arrhythmias.³ In this case, if the pacemaker were interrogated earlier, the cause of the seizure would have been identified as a dramatic loss of blood pressure due to a VT/VF event. It would have allowed arrangements to be made for an implantation of an ICD at that time or treatment modification. We recommend interrogation of any device as a part of the standard work-up for syncope. Proper programming of the stored electrograms can give insight into any arrhythmic event.⁴ In this case, the stored electrograms were left at nominal settings, which were “freeze”. After the storage of 4 electrograms, the device stopped recording electrograms.⁵ It is possible that the patient could have had additional nonsustained episodes subsequent to the one recorded on July 7, 2009. In this case, the “continuous” mode would have allowed the device to continue storage of IEGMs albeit at the expense of overwriting old events with new ones.6 It is not only important to program the EGM storage on, but it is also imperative the diagnostics of the new-generation pacemakers are programmed effectively in order to optimize the device for the patient’s medical management. 

References

1. Huikuri H. Effect of stored electrograms on management of the paced patient. Am J Cardiol 2000;86:101K–103K.
2. Nowak B, Sperzel J, Rauscha F, et al. Diagnostic value of onset-recordings and marker annotations in dual chamber pacemaker stored electrograms. Europace 2003;5:103–109.
3. Paraskevaides S, Giannakoulas G, Polymeropoulos K, et al. Diagnostic value of stored electrograms in pacemaker patients. Acta Cardiol 2008;63:59–63.
4. Patel V, Nayak H, Marchlinski F. Interpretation and application of stored electrograms. Clin Electrophys Rev 2001;5:96–103.
5. Kusumoto F, Goldschlager NF. Cardiac Pacing for the Clinician. New York, NY: Springer, 2008, p.673.
6. Kenny T. The Nuts and Bolts of Paced ECG Interpretation. Hoboken, NJ: Wiley-Blackwell, 2009, p.99.

Editor’s Note: This article underwent peer review by one or more members of EP Lab Digest’s editorial board.

Disclosures: William DeForge, PhD, CCDS discloses that he is an employee of St. Jude Medical. Jaclyn Conelius has no disclosures to report.