Featured Case

Instant Upgrade for Single-Chamber ICD Patient with Heart Block

Mark Mascarenhas, MD

Jersey Shore University Medical Center, Neptune City, New Jersey

Mark Mascarenhas, MD

Jersey Shore University Medical Center, Neptune City, New Jersey

Case Description

The patient is a 62-year-old male who was a 9/11 firefighter. He was implanted with a primary prevention ICD in late 2015. Since he did not have indications for a dual-chamber device, he was implanted with the Itrevia 7 VR-T DX ICD (BIOTRONIK), which provides ICD therapies, ventricular pacing, and dual-chamber sensing. The device uses the Linox DX lead 65/17 with floating atrial dipoles, which offer the ability to sense atrial activity. The implantation procedure was unremarkable, and the patient was discharged home in good condition. He adjusted well to his new life as a primary prevention ICD patient, and his first follow-ups showed good progress. The ventricular lower rate limit was programmed to 40 ppm as the patient had no pacing indications and was not expected to need pacing support. Since device implantation, he has had no shocks.

He returned to the clinic in early autumn of 2019, complaining of feeling unwell. An ECG showed atrial and ventricular events almost on top of each other, suggesting an atrioventricular nodal reentrant tachycardia (AVNRT), a paroxysmal supraventricular tachycardia that is perpetuated by a reentrant circuit either within or very close to the AV node (Figure 1). For a true differential diagnosis of AVNRT, an EP study was needed, but atrial and ventricular events gave a suspicion it could be AVNRT. While AVNRT could not be confirmed without an EP study, a conservative approach to AVNRT was attempted. The patient was treated with the Valsalva maneuver, a type of vagal maneuver intended to break the AVNRT. The Valsalva maneuver requires that the patient bear down as if they were having a bowel movement while trying to exhale forcefully against a closed airway; this maneuver stimulates the vagus nerve by exhaling against a closed glottis. In this case, the Valsalva maneuver promptly interrupted the AVNRT and normal sinus rhythm was restored. The patient recovered and went home with no further episodes.

In November 2019, the patient returned to the emergency room complaining that he was presyncopal, felt dizzy and unwell, and was concerned about his heart. An ECG revealed that the patient had third-degree heart block. In third-degree or complete heart block, the atria and ventricles dissociate, which deprives the patient of the benefits of 1:1 AV synchrony (Figure 2). Having third-degree heart block is an indication for a dual-chamber pacing device to restore AV synchrony, which for most patients with a single-chamber ICD would mean ICD revision surgery, including the implantation of a new lead in the atrium. This would expose the patient to another surgery, device replacement, and the placement of a second lead.

However, this patient had a BIOTRONIK DX ICD system, which could be programmed in one simple programming step from VVI pacing to VDD pacing. No additional or revised lead was required. The Linox DX lead facilitates upgrade to a VDD configuration in that it offers atrial sensing, which in turn, allows the Itrevia device to synchronize ventricular pacing to intrinsic atrial activity. Thus, Itrevia programmed to VDD pacing can provide AV synchrony for patients with complete heart block. After a few minutes of VDD pacing, the patient felt much better and was able to return home. He has had no further episodes.


The benefit of the BIOTRONIK DX system was that the system operated originally as an ICD with VVI pacing capability for primary prevention, but allowed for an “instant upgrade” to VDD with one programming step. This spared the patient a surgical intervention and reduced the costs of having to explant one device to upgrade it to a new device. In addition, the DX lead was already in place, and no additional leads were required (Figure 3).

Heart disease can be progressive and arrhythmias may develop in patients with no prior history of arrhythmic activity. There are many potential causes of heart block, including ischemic heart disease as well as fibrosis, medications, infectious diseases, certain conditions such as hypertrophic obstructive cardiomyopathy, and others.1 Heart block may be paroxysmal, intermittent, or even permanent, which can make it potentially life threatening.2 However, for primary prevention patients such as this firefighter with no conventional pacing indications, a single-chamber ICD (VVI pacing) is preferred and a dual-chamber system confers no specific advantages.3,4 A patient histogram demonstrates pacing rates during this period (Figure 4).

The combination of the DX lead with its floating atrial dipoles and the DX algorithm was created for atrial diagnostics, but it is equally capable of offering VDD pacing, which has shown to benefit patients with heart block.5 In fact, a comparative appraisal of VDD compared to DDD pacing for patients with symptomatic forms of AV block found VDD to be a viable alternative to the more expensive DDD pacing mode and VDD pacing.6 Furthermore, VDD pacing reduces not only the need for revision surgeries but also healthcare costs without compromising patient safety and well-being. 

The SENSE trial, which evaluated 150 patients with BIOTRONIK DX devices using a DX lead with floating atrial dipoles, found that DX devices could detect atrial high-rate episodes, sometimes called subclinical atrial fibrillation, equivalent to dual-chamber devices (P=1.0).8 The ASSERT and TRENDS randomized clinical trials have demonstrated that subclinical AF is prevalent, and early detection of such atrial arrhythmias may help facilitate diagnosis and treatment.9,10

Primary prevention patients without an atrial pacing indication and with a normal left ventricular ejection fraction are appropriately treated with an ICD capable of defibrillating the heart; pacing is typically left to VVI at a low base rate. Many of these patients never develop other arrhythmias or require more than occasional basic single-chamber pacing. However, a subpopulation of these patients may develop arrhythmias that require various forms of intervention.11 The particular advantage to this individual patient was that his DX ICD system could be upgraded to restore AV synchrony with a single, painless programming step instead of a surgical procedure, new device, and implantation of a second lead. The clinically documented advantages of the DX system should always be considered for primary prevention patients because cardiac disease tends to be progressive and this system offers great flexibility in addressing new arrhythmias that may emerge. 

This article is published with support from BIOTRONIK.

Disclosure: Dr. Mascarenhas has no conflicts of interest to report regarding the content herein.   

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