De Novo Implantation of Two-lead Cardiac Resynchronization Therapy System With Atrioventricular Synchrony Detects Subclinical Atrial Fibrillation and Nonsustained Ventricular Tachycardia, While Delivering Optimal CRT

For patients without an atrial pacing indication, a CRT-DX system (single-pass implantable biventricular cardioverter-defibrillator) can pace the right and left ventricles with two leads, while maintaining AV synchrony. This is achieved with a DX lead affixed in the right ventricle with floating atrial dipoles to sense atrial activity through the atrial blood pool, and V-V timing synchronized/programmed with the quadripolar left ventricle lead. Any device that dispenses with the atrial lead can offer multiple advantages: the use of fewer leads reduces the chance of lead-related complications, shortens implant time, and costs less¹ than systems with an atrial lead. Fewer leads in the body can prevent vascular occlusion, particularly in smaller-framed patients or patients who already have abandoned indwelling leads.² However, the main drawback of devices without an atrial lead has always been loss of AV synchrony as well as lack of atrial arrhythmia detection and quantification, making them unsuitable for patients with or at risk for certain types of arrhythmias. The use of a CRT-DX system offers the same therapeutic benefits of standard CRT,³ without loss of AV synchrony and atrial surveillance. DX technology-based devices from BIOTRONIK provide two-lead biventricular pacing, rescue defibrillation, and a dedicated atrial channel, offering atrial electrograms.⁴

Unlike older single-pass VDD pacemaker systems, the DX devices rely on a proprietary lead with proximal floating dipole atrial sensing and a unique atrial input amplifier and signal filtration system in the device.^3,5 The THINGS Registry found that detection of high-rate atrial activity was nearly four-fold greater with DX devices compared to the single-chamber ICD.⁶

Minimizing hardware in the body has important clinical benefits. In the SENSE clinical trial (n=150), conventional dual-chamber ICDs were compared with single-pass DX devices from BIOTRONIK and found that the single-pass systems could detect high-rate atrial activity, including subclinical atrial fibrillation (AF), as well as dual-chamber systems.⁷ In some patients, VDD is quite comparable to DDD pacing; in a study of patients with symptomatic AV block, VDD was able to maintain 94% to 99% AV activation.⁸ Event-free survival in patients with AV block randomized to be treated with VDD or DDD pacemakers found similar results, with 83.4% survival for VDD and 84.9% for DDD at a mean follow-up time of 42±15 months.¹

The implications are likewise profound for the healthcare system. While single-pass VDD systems are not right for all patients, less than half of newly indicated ICD patients do not require atrial pacing.⁹ For those patients, DX technology offers comparable effectiveness and safety at about 9% lower implant costs,¹ 40% fewer complications, and 45% lower mortality risk.⁹ In a study of 1517 pacemaker patients, dual-chamber devices (two-lead systems) were an independent predictor for long-term complications compared to a single-lead device.¹⁰ A study of 274 congenital heart disease patients found that at a median follow-up period of 12 years, 34.6% of patients experienced some form of device-related complication, of which lead-related complications were most frequent (24.8%).¹¹ It is important to note that risk of lead-induced venous occlusion seems to increase with each additional lead implanted.²

Nevertheless, some patients require an atrial lead for atrial pacing support or to monitor atrial activity, such as AF with rapid ventricular response. Selecting the optimal device for a patient can be challenging as health conditions are dynamic, and previously undetected AF has been linked to higher mortality risk in heart failure patients.¹²

The patient was a 68-year-old man with nonischemic cardiomyopathy despite guideline-directed medical therapy; he also had left bundle branch block (LBBB). He presented to the clinic with typical heart failure symptoms. An initial echocardiogram was performed, showing his left ventricular ejection fraction (EF) was approximately 25%. His QRS duration was 152 ms. Multiple tests were performed over the course of several weeks, and although he had normal perfusion, his EF remained consistently low and was never above 30%. His pharmacological regimen was lisinopril 5 mg, atorvastatin 10 mg, glucosamine 500 mg, and carvedilol 6.25 mg BID, along with low-dose aspirin 81 mg. Despite aggressive medical therapy, his heart failure symptoms and LV dysfunction persisted. No signs or symptoms of AF had been reported.

The patient was told about the option of a biventricular ICD to provide cardiac resynchronization therapy (CRT) to improve his cardiac output and also offer rescue defibrillation. After informed consent, the patient was implanted with an Intica 7 HF-T QP device (BIOTRONIK) with a right ventricular lead with floating atrial dipoles and a quadripolar left ventricular lead. No lead was implanted in the atrium. An important consideration for implant is selection of the appropriate lead spacing for the individual patient’s anatomy; there are two atrial dipole spacing options available, though the 15 cm spacing is used more often at our facility. The implant was uneventful and the patient was discharged with no complications. After device implant, the atrial electrogram reported short spells of self-terminating and asymptomatic episodes of AF (Figure 1). His minimum atrial rate was 60 bpm. Anticoagulation therapy was commenced.

The patient was monitored for over two years, and during this time, there was no therapy delivery for a potentially life-threatening ventricular arrhythmia. The QRS duration decreased to 112 ms with 98% biventricular pacing (atrial sensed/ventricular paced 99%) (Figure 2). The patient reported feeling well. His p-wave amplitude had a mean value >8 mV and a minimum value of 7.6 mV two years post implant.

More recently, the device properly reported asymptomatic, nonsustained ventricular tachycardia (NSVT), evident on the device electrogram (Figure 3). This condition was closely monitored using the alert system.

DX device therapy brought about remarkable improvements in this patient. At about 11 months post implant, his EF improved to around 35% to 40%, which he has maintained. His functional status improved as well, and he can currently walk three miles. His heart failure-associated symptoms have resolved as well. He remains on anticoagulation therapy and NSVT is being monitored.

The use of a CRT-DX device in this particular patient provides reassurance that the clinic can monitor his arrhythmias safely and efficiently without the need for an atrial lead. In fact, the use of this device provides the patient not only with beneficial biventricular pacing support, but it also offers immediate monitoring, classification, and quantification of any high-rate atrial activity.

Acknowledgements: This article was prepared with medical editing and writing support by Jo Ann LeQuang, whose fees were covered by BIOTRONIK.

This article is published with support from BIOTRONIK.

Disclosure: Dr. Borge has no conflicts of interest to report regarding the content herein. Outside the submitted work, he reports payment or honoraria as a speaker for BIOTRONIK and trainer for Boston Scientific; he also reports participation on an advisory board for Abbott.