A Novel Solution for Detecting Subclinical Arrhythmia in Patients Who Require a Single-Chamber ICD

Antony F. Chu, MD Rhode Island Hospital Providence, Rhode Island
Antony F. Chu, MD Rhode Island Hospital Providence, Rhode Island

Atrial fibrillation (AF) and atrial flutter are well known as the most common arrhythmias1 in clinical practice. It has been estimated that by 2050 more than 12 million people in the U.S. will have this condition,2 which is associated with significant morbidity and mortality.2 Cardiologists and electrophysiologists are well aware of the challenges presented by AF and atrial flutter management, and that a diagnosis of AF and/or atrial flutter complicates the management of any other co-morbid condition.3 Medicare data indicate that the diagnosis of AF results in significantly increased incremental costs of clinical management,3 and clinicians are aware of the implications and consequences to patients if the AF or atrial flutter is subclinical.4 

Case Description

We present a case report on a 76-year-old male patient with a history of ischemic cardiomyopathy and an LVEF of 30% implanted with a BIOTRONIK DX System for primary prevention indication. Pre-implant workup indicated no documented arrhythmia, nor complaints of palpitations, syncope or pre-syncope.5 

The ICD implant was unremarkable. Venous access was obtained via cutdown of the left cephalic vein. Implantation of a BIOTRONIK Lumax 740 VR-T DX single-chamber ICD was routine with no complications. The Linoxsmart S DX 65/17 lead with atrial dipole was placed in a low- to mid-septal position (Figure 1). Values obtained at implant revealed P-waves of 2.8-5.6 mV, R-waves 12.7-14.9 mV, and right ventricular pacing thresholds of 0.4 V at 0.4 ms (measured via the ICD). The pacing lead impedance at implant was 534 ohms. No diaphragmatic stimulation was observed.

An examination of the IEGM obtained via the ICD (Figure 2) revealed an atrial flutter with AV block resulting in a fairly regular ventricular response. The atrial cycle length was about 200 ms with a ventricular response of about 600 ms.

Routine pre-discharge evaluation of the system was performed the day after implant. P-waves (during atrial flutter) were 3.0-4.8 mV, R-waves were 17.9-19.6 mV, and right ventricular pacing thresholds at 0.4 V at 0.4 ms with pacing lead impedance of 577 ohms were observed. The atrial burden was 97.4% overnight, indicating an almost constant atrial flutter since implant. The ventricular response appeared to be regular (Figure 3), and the patient denied overt symptoms related to the atrial flutter.


Atrial diagnostics and monitoring theoretically provide at least two benefits to patients with an implanted ICD system. Data provided by the atrial channel, when combined and analyzed with data proved by the ventricular channel, forms the basis for device-based algorithms designed to reduce the likelihood of therapy for a non-lethal supraventricular tachycardia (SVT). Although specificity and positive predictive value has been demonstrated by these various proprietary algorithms in classifying rhythms,6-11 the effect any particular algorithm has on reducing overall morbidity and mortality remains subject to lively clinical debate.12,13  However, the data provided by the atrial channel are useful to the clinician in a much more prosaic way — in monitoring for atrial arrhythmia.

In a population of over 2,500 patients implanted with a pacemaker or ICD, and without a history of AF (but with hypertension), Healy et al report that within three months of implant, more than 10% had subclinical atrial tachycardia (primarily AF) as detected by device diagnostics (p = .001).4 These atrial tachyarrhythmias were associated with an increased risk of stroke or peripheral emboli (p = .007). Given that 15% of strokes are attributable to AF14 and that about 25% of strokes have an unknown etiology,15 the utility of atrial monitoring, especially when one accounts for the increasing risk of AF as one ages16 and the average age of ICD patients,17 is obvious.

In this case study, the diagnosis of atrial flutter is important as the arrhythmia was not previously diagnosed. The patient was appropriately transitioned to anticoagulation for mitigation of thromboembolic stroke risk. Additionally, atrial flutter may have been a contributing factor to this patient’s left ventricular dysfunction via a tachycardia-induced cardiomyopathy. 

Until recently, atrial diagnostics and monitoring in an ICD system required the implantation of an atrial lead (i.e., a dual-chamber ICD system). Although ACC/AHA/HRS ICD implant guidelines may recognize the utility of a dual-chamber ICD system implanted in the absence of a strict pacing indication,18 CMS guidelines do not,19 forcing the implanter potentially to make a choice between a medical necessity and a Medicare regulation. Complicating this decision are the data from a recent analysis of the NCDR database. Dewland et al report that adverse events and in-hospital mortality were more frequent in dual-chamber than single-chamber ICD recipients.20 Additionally, procedure times and exposure to fluoroscopy are likely greater with implantation of a dual-chamber versus single-chamber device.

The BIOTRONIK DX System offers a novel solution to the dilemma. The system includes a modified Linoxsmart ICD lead consisting of an active-fixation, dedicated bipolar lead with a single high-voltage coil and an atrial sensing dipole on a single lead. The ICD itself is specially modified to work with this lead to optimize atrial signal processing. In other respects, the system resembles a conventional ICD. The Lumax DX system permits dual-chamber ICD diagnostics, monitoring, and rhythm classification on a single lead system, which should translate into reduced implant risk for patients and the potential for atrial arrhythmia monitoring with subsequent identification and management of subclinical atrial tachycardia.

Disclosure: Dr. Chu reports no conflicts of interest regarding the content herein. Outside the submitted work, Dr. Chu reports receiving honoraria as part of a speaker’s bureau by BIOTRONIK, and fellowship grants to his institution.  


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