Concurrent lead impedance reduction in both leads of a dual-chamber pacemaker secondary to generator defect

Key Teaching Points.

• •If multiple leads drop impedance within a short period, it might be potentially linked to the device header.
• •Recognizing this issue can prevent unnecessary lead revisions.
• •Examining mode switch episodes becomes crucial to confirm the problem is true atrial tachyarrhythmia and ensure appropriate action is taken.

Introduction

Pacing malfunction can arise from structural integrity failure of the leads, and one of the main causes of lead integrity failure is insulation breach, which is recognized by low impedance. We present a rare case of decreased impedance in both right atrial (RA) and right ventricular (RV) leads of a dual-chamber pacemaker owing to generator failure with intact lead insulation. The removed device analysis revealed a bonding anomaly between the header and base can, leading to fluid ingress electronic circuitry damage that led to measured low impedances. Timely recognition of the generator defect prevented unnecessary lead revision.

Case report

The patient, a 61-year-old woman with a past medical history significant for hypertension, bicuspid aortic valve status post transcatheter aortic valve replacement and managed on warfarin, obstructive sleep apnea, and sick sinus syndrome underwent dual-chamber pacemaker (St. Jude Medical 2272 Assurity MRI) implant with 2088TC Tendril STS leads (St. Jude Assurity MRI©; St. Jude Medical, St. Paul, MN) in September 2019 owing to symptomatic bradycardia and chronotropic incompetence. At the time of implantation, lead impedances were measured at 550 ohms for the RA lead and 700 ohms for the RV lead. In October 2021, the device was part of a safety advisory for premature battery depletion.

Over the next 3 years, pacemaker evaluations consistently showed AV sequential pacing, indicating normal device function. The impedance ranges in both leads were within the expected range, measuring between 350 ohms and 500 ohms. However, in later pacemaker evaluations, instances of automatic mode switching (AMS) were observed. Further examination via electrograms identified these occurrences as originating from atrial lead noise. Notably, the frequency and duration of these AMS episodes have gradually escalated over time.

The device was reprogrammed to DDIR (dual-chamber rate responsive system) in response to this issue. During follow-up interrogation, it was noted that the atrial lead ceased sensing any atrial activity even though surface leads had prominent p waves (Figure 1). Upon a detailed examination, it was discovered that the atrial impedance had dropped significantly, measuring <100 ohms (specifically 62.5 ohms) for the first time in early September 2023. This decrease in impedance was consistent in both bipolar and unipolar configurations. In contrast, the RV lead impedance remained at 375 ohms. Interestingly, despite this impedance change, the capture threshold remained relatively unchanged. Although the clinical advisory was known since 2021, lead impedance abnormalities were only identified 2 years later, in 2023.

Figure 1.

Results showing lack of sensing of the P wave.

Given these findings, the patient was scheduled for RA lead revision to address the issue and restore proper atrial sensing and pacing functionality.

While the patient was awaiting the atrial lead revision procedure 2 weeks after the RA lead impedance alert, a transmission alert indicated a concurrent decrease in RA and RV lead impedance (Figure 2). Notably, the patient remained asymptomatic during this episode. Interrogation revealed RV lead impedance at 62 ohms with a bipolar capture at 1.5 V at 0.5 ms and unipolar capture at 1.25 V at 0.5 ms. Despite performing provocative maneuvers, no RA or RV lead noise was observed.

Figure 2.

Results showing concurrent right atrial and right ventricular lead low impedance alert values.

In response to these findings, 2 days later, the patient underwent an exploratory procedure with the intent of possible lead revision after a comprehensive intraprocedural integrity assessment. During the procedure, the leads were disconnected from the generator and connected to the PSA (Pacing System Analyzer) for a thorough examination. There was no evidence of premature battery depletion, with a remaining battery life of approximately 5 years. A complete interrogation was performed without any evidence of lead integrity problems. Satisfactory pacing thresholds and P waves were likewise obtained.

Subsequently, the existing leads (2088TC Tendril STS) were connected to a new pulse generator (Boston Scientific, Marlborough, MA). Both capture and impedance were assessed to be within normal ranges (RA 525 ohms and RV 636 ohms), confirming the resolution of impedance issues.

The postoperative evaluation at 12 weeks postimplantation revealed normal AV sequential pacing at 70 beats per minute and normal device function. No mode switches occurred during these 12 weeks.

Discussion

AMS algorithms in permanent pacemakers were designed to prevent the tracking of rapidly occurring signals, specifically supraventricular tachycardias sensed by the atrial channel. The aim is to mitigate adverse hemodynamic effects and alleviate symptomatic consequences of a rapid ventricular response. Importantly, these programs also provide data on the time of onset and duration of AMS episodes.

In certain instances, however, noise on the atrial lead can inadvertently trigger mode switching, as was observed in the case described (Figure 3A and 3B).

Figure 3.

A: Automatic mode switching (AMS) episodes triggered lead noise. B: Noise of atrial lead causing AMS.

In our case, device interrogation showed the low-amplitude oscillations were confined only to the atrial electrode and no history of exposure to unusual sources consistent with electromagnetic interference as a source. Lack of noise reproducibility with maneuvers like isometric upper limb exercise and pocket manipulation reduced the possibility of myopotentials. Mode switching must be reviewed before confirmation of atrial arrhythmia that may merit anticoagulation.

Given the low RA lead impedance and the advisory on accelerated battery depletion, we initially suspected this could be secondary to insulation failure. However, the subsequent fall in impedance of both leads was somewhat atypical, suggesting either insulation failure with the RA/RV lead-header interface or the pulse generator itself. During the initial lead integrity assessment while connected to the device, we ensured pins were appropriately placed and the ratchet was properly tightened before lead removal. After that, the PSA confirmed that the leads were intact, and the impedance alerts were related to either a header or generator issue. Notably, the device was part of the 2021 advisory on epoxy header malfunction.

We are unaware of concurrent atrial and ventricular lead malfunction alerts as part of this advisory. No mode switch events have occurred since the generator replacement for the past 12 weeks. Still, long-term follow-up is required before confirmation and assessment of the burden of atrial arrhythmia.

Conclusion

When associated with low impedance, the concurrent malfunction of both atrial and ventricular leads should raise concerns about the generator itself. Considering the device’s history and that it is part of an advisory on epoxy header malfunction, the suspicion on the generator further strengthened and prevented unnecessary lead revision.

Disclosures

None.