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

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 Linox^smart 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.

Discussion

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 Linox^smart 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.  

References

1. Dash S, Chon KH, Lu S, Raeder EA. Automatic real time detection of atrial fibrillation. Ann Biomed Eng. 2009;37:1701-1709.
2. Centers for Disease Control and Prevention, Division of Heart Disease and Stroke Prevention, https://www.cdc.gov/dhdsp/data_statistics/fact_sheets/fs_atrial_fibrillation.htm. Accessed April 8, 2013.
3. Kim M, Johnston SS, Chu BC, Dalal MR, Schulman KL. Estimation of total incremental health care costs in patients with atrial fibrillation in the United States. Circ Cardiovasc Qual Outcomes. 2011;4:313-320.
4. Healy JS, Connolly SJ, Gold MR, et al. Subclinical atrial fibrillation and the risk of stroke. N Engl J Med. 2012;366;2:120-129.
5. Results may be unique to this patient.
6. Summary of Safety and Effectiveness, Phylax AV PMA Submission, P000009, Sept. 2000. 
7. Wilkoff BL, Kühlkamp V, Volosin K, et al. Critical analysis of dual-chamber implantable cardioverter defibrillator arrhythmia detection: results and technical considerations. Circulation. 2001;10:381-386.
8. Dorian P, Philippon F, Thibault B, et al. Randomized controlled study of detection enhancements versus rate-only detection to prevent inappropriate therapy in a dual-chamber implantable cardioverter-defibrillator. Heart Rhythm. 2004;1:540-547.
9.  Friedman PA, McClelland RL, Barmlet WR, et al. Dual-chamber versus single-chamber detection enhancements for implantable defibrillator rhythm diagnosis: the detect supraventricular tachycardia study. Circulation. 2006;113:2871-2879.
10. Sinha A, Stellbrink C, Schuchert A, et al. Clinical experience with a new detection algorithm for differentiation of supraventricular from ventricular tachycardia in a dual-chamber defibrillator. J Cardiovasc Electrophysiol. 2004;15:646-652.
11. Hintringer F, Deibl M, Berger T, Pachinger O, Roithinger FX. Comparison of the specificity of implantable dual chamber defibrillator detection algorithms. Pacing Clin Electrophysiol. 2004;27:976-982.
12. Ha AH, Ham I, Nair GM, et al. Implantable cardioverter-defibrillator shock prevention does not reduce mortality: a systemic review. Heart Rhythm. 2012;9:2068-2074.
13. van Rees JB, Borleffs CJ, de Bie MK, et al. Inappropriate implantable cardioverter-defibrillator shocks: incidence, predictors, and impact on mortality. J Am Coll Cardiol. 2011;57:556-562.
14. National Stroke Association, https://www.stroke.org/site/PageServer?page
15. name=risk. Accessed April 8, 2013.
16. Wolf PA, Dawber TR, Thomas HE Jr, Kannel WB. Epidemiologic assessment of chronic atrial fibrillation and risk of stroke: the Framingham Study. Neurology. 1978;28:973-977.
17. Marinigh R, Lip GY, Fiotti N, Giansante C, Lane DA. Age as a risk factor for stroke in atrial fibrillation patients implications for thromboprophylaxis: implications for thromboprophylaxis. J Am Coll Cardiol. 2010;56:827-837.
18. Katlic, Mark R. Cardiothoracic Surgery in the Elderly Evidence-Based Practice. New York: Springer, 2011. Pg 444.
19. Russo A, Stainback RF, Bailey SR, et al. ACCF/HRS/AHA/ASE/HFSA/SCAI/SCCT/SCMR 2013 appropriate use criteria for implantable cardioverter-defibrillators and cardiac resynchronization therapy: a report of the American College of Cardiology Foundation appropriate use criteria task force, Heart Rhythm Society, American Heart Association, American Society of Echocardiography, Heart Failure Society of America, Society for Cardiovascular Angiography and Interventions, Society of Cardiovascular Computed Tomography, and Society for Cardiovascular Magnetic Resonance. Heart Rhythm. 2013;10;4:e11-58.
20. National Coverage Determination (NCD) for Implantable Automatic Defibrillators, https://www.cmms.hhs.gov/medicare-coverage-database/details/ncd-details.aspx?NCDId=110&ncdver=3&TAId=15&bc=BAAAgAAAAAAA&. Accessed online April 8, 2013.
21. Dewland TA, Pellegrini CN, Wang Y, Marcus GM, Keung E, Varosy PD. Dual-chamber implantable cardioverter-defibrillator selection is associated with increased complication rates and mortality among patients enrolled in the NCDR implantable cardioverter-defibrillator registry. J Am Coll Cardiol. 2011;58:1007-1013.