Novel Single-lead ICD Provides SVT Discrimination and Atrial Diagnostics

Salam Sbaity, MD and Kandis Ciesielski, BSN, RN, Cedar Valley Medical Specialists, Waterloo, Iowa
Salam Sbaity, MD and Kandis Ciesielski, BSN, RN, Cedar Valley Medical Specialists, Waterloo, Iowa


A current debate in electrophysiology concerns the benefits of SVT discrimination algorithms versus the risks associated with atrial lead implantation in ICDs. A number of clinical studies have called into question the reliability of SVT discrimination to reduce inappropriate therapies for non-life-threatening arrhythmia, especially in primary prevention patients.1,2

Of equal concern are data that suggest atrial lead implantation involves more risk and an increase in complications for ICD patients without offering improvement in outcomes.3-5

Based on these data, one might be convinced that single-chamber ICDs provide the safest and most effective choice of therapy for patients with an indication for an ICD. However, many clinicians argue for the implantation of dual-chamber ICDs due to the prevalence of atrial arrhythmias in the ICD-indicated patient population. The outcome for the patient can include stroke and increasing heart failure symptoms if atrial fibrillation (AF) goes undiagnosed and untreated.6 Atrial lead diagnostics and intracardiac electrograms (IEGMs), coupled with the ability of the implanted device to monitor 24/7, can be very helpful in making the diagnosis of subclinical AF in patients with implanted devices.7

Case Study

We present a case study of a 71-year-old male patient implanted with an ICD for documented ventricular tachycardia (VT) at 140 bpm refractory to medication therapy in the ER. Past medical history included CAD, CABG, and a recent episode of VT without syncope but with dizziness and chest pressure.

In June 2013, this patient underwent implantation of a single-chamber BIOTRONIK DX ICD. This single-lead ICD includes provisions for atrial sensing, atrial diagnostics, and SVT discrimination; these are accomplished by using a Linox S DX ICD lead, which is a single-coil ventricular lead with an atrial dipole. The Linox S DX ICD lead provides high-voltage and pacing therapies in the ventricle as well as atrial sensing. The ICD circuitry is specifically designed for improved atrial sensing when using this lead.

The implant was unremarkable. P-waves averaged 5.1 mV and R-waves 12.3 mV. The ventricular pacing threshold was 0.5 V @ 0.4 ms and the pacing lead impedance was 608 ohms. The patient was discharged with the ICD programmed to VVI 40 PPM, 3-zone detection, with ATP burst for VT-1 (136 bpm) ATP and shocks for VT-2 (188 bpm) and ATP one shot attempt followed by shocks for VF (214 bpm). The wireless remote Home Monitoring® feature was enabled.

In the 5 months since implantation, this patient has had 13 episodes recorded in diagnostic memory (not counting defibrillation testing). Of these, 11 were SVT falling into the VT-1 zone, for which therapy was appropriately withheld (Figure 1); 2 episodes were true VT in the VT-1 zone, which were successfully treated with ATP (Figure 2). All of these episodes were evaluated remotely as they occurred. The patient was also then evaluated in the office for further management of his VT. This system has reliably discriminated between SVT and VT with similar ventricular rates. During the follow-up period, atrial and ventricular sensing have remained robust and stable, and chronic pacing thresholds remain less than 1.0 V.


Note the similarity in the stored far-field (FF) IEGM signals for the 2 episodes shown, which are representative of the stored episodes. In the absence of atrial lead information, we feel we would not have been able to reliably determine if the episodes were untreated VT, or SVT for which therapy was withheld. The addition of atrial IEGM provides confirmation that the rhythm discriminator both appropriately withheld and treated the different episodes. In fact, clinical evidence suggests that the use of atrial IEGMs dramatically improves a clinician’s accuracy of rhythm classification.8 These data indicate that by adding atrial lead information, an experienced clinician’s accuracy improves by as much as 22–45% in discriminating SVT from VT without negatively affecting the accuracy of diagnosing VTs. Without atrial diagnostics, it is relatively easy for the clinician to misclassify the SVT as VT if relying on the FF and IEGMs alone.

The single-lead ICD discussed here can also be implanted with less hardware and thus presumably with less risk to the patient. The device is optimized to perform with a lead system that is sophisticated in terms of sensing and therapy, but includes a single coil should extraction ever be required. The system is connected to a robust remote monitoring system that provides device/lead and diagnostic updates to the system daily, without patient interaction. The system includes atrial lead information and diagnostics that permit the clinician to monitor and evaluate the appropriateness of device programming and interventions. The remote monitoring system can also be programmed to alert the clinician of a new-onset arrhythmia almost immediately, providing an opportunity for early intervention.


All clinicians want to avoid untoward events and complications for their patients. Modern day healthcare reform may impose significant penalties to providers if quality measures are not met. Physicians, allied professionals and hospitals are under increasing surveillance today regarding the appropriateness of prescribed therapy.9,10 Recent CMS policy changes mean that failure to meet standards for a defined set of diagnosis-related groups (DRGs) will affect reimbursement for all DRGs. Clinicians can expect more oversight on decisions as well as continuing pressure to control costs of therapy and the means used to provide it. The pressure to control healthcare costs will only increase. Diagnostics that increase appropriate diagnosis and improve utilization of evidence-based practice not only improves patient outcomes, but also may reduce overall healthcare costs.

Disclosures: The authors have no conflicts of interest to report regarding the content herein. 


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