Leadless Pacemaker Implantation in a Patient With Diminutive Subclavian Veins

Background. Conventional pacemakers have a longstanding history of preventing morbidity and mortality in patients with bradyarrhythmia and conduction disorders. While decades of advancements have improved pacemaker technology and implantation technique, insertion of transvenous leads and formation of a pectoral pocket can lead to complications, including pocket hematoma, pneumothorax, or infection.Leadless pacemakers were introduced in 2012 to address these complications; however, early leadless systems only provided single-chamber ventricular pacing. In 2020, an accelerometer-based atrial sensing feature was developed to allow for atrioventricular (AV) synchrony with these devices. Early evidence suggests that patients with sinus rhythm and AV block can benefit from single-chamber leadless pacing systems with an AV synchrony algorithm.As availability of these devices continues to broaden, identification of appropriate recipients has become increasingly relevant.

J INVASIVE CARDIOL 2022;34(2):E114-E116. Epub 2022 January 6.

Key words: atrioventricular synchrony, AV block, leadless pacemaker

Conventional pacemakers have a longstanding history of preventing morbidity and mortality in patients with bradyarrhythmia and conduction disorders.^1,2 While decades of advancements have improved pacemaker technology and implantation technique, insertion of transvenous leads and formation of a pectoral pocket can lead to complications, including pocket hematoma, pneumothorax, or infection.^3-5 Leadless pacemakers were introduced in 2012 to address these complications.^6,7 These devices are implanted using a percutaneous femoral, catheter-based approach to advance the device to the right ventricle (RV) and fix it to the myocardium with nitinol tines. A number of prospective trials have since been used to compare conventional and leadless pacemakers and have found that they have comparable short-term safety and efficacy.^8-10 Unsurprisingly, implantation of leadless pacemakers is not associated with pneumothorax, pocket hematoma, or pocket/lead infection, but is associated with femoral vascular complications and a moderate risk of cardiac perforation.¹¹ Overall, conventional pacemakers have a slightly better short-term complication rate than leadless pacemakers (4.0% vs 4.8%, respectively), which may be attributed to procedural learning curve.¹² Comparison of 12-month outcomes reveal that leadless pacemakers have a 71% reduction in complications compared with conventional transvenous systems.¹¹ Early leadless systems only provided single-chamber ventricular pacing. On January 21, 2020, an accelerometer-based atrial sensing feature has been developed to allow for atrioventricular (AV) synchrony with these devices. Early evidence suggests that patients with sinus rhythm and AV block can benefit from single-chamber leadless pacing systems with an AV synchrony algorithm.¹³ The estimated battery life for the Micra AV device (Medtronic) is 8-13 years depending on the pacing mode, often exceeding that of conventional pacemakers, which last about 7-10 years.^14,15 As availability of these devices continues to broaden, identification of appropriate recipients has become increasingly relevant.

A 71-year-old man presented with second degree AV block with 2:1 conduction at a heart rate of 36 beats/min. He was admitted for suspected right lower-extremity (RLE) deep vein thrombosis (DVT). RLE duplex revealed a superficial venous thrombus within the distal right greater saphenous vein, but no DVT. He had a past medical history of intermittent AV block, coronary artery disease with stenting in December of 2020, hypertension, and DVT in 2019. The patient was on apixaban prior to admission, which was switched to rivaroxaban on discharge. Telemetry showed that the patient was bradycardic with heart rates in the 40 beats/min range. Left-sided dual-chamber conventional pacemaker insertion was attempted. The plan was for the RV lead to be placed in a septal location to capture the patient’s conduction system and prevent worsening left ventricular (LV) function. However, intraoperative left-sided venogram showed diminished venous flow along the left subclavian vein.

The procedure was aborted due to diminutive subclavian veins impeding access and lead placement. A chest computed tomography (CT) with contrast revealed both left and right subclavian vein narrowing, posing a barrier to conventional pacemaker implantation (Figure 1).

The patient continued to have symptomatic bradycardia and progressed to intermittent complete heart block (CHB) during his hospitalization. Because standard pacemaker implantation was limited by narrow subclavian veins, leadless dual-chamber pacemaker implantation was attempted through the right femoral vein. A Micra AV device was selected because of its ability to provide AV synchrony. The device was deployed on the patient’s RV septum, capturing the conduction system without complications. The patient was subsequently observed to have an appropriately functioning device, with atrial-sensed and ventricular-paced rhythm during inpatient follow-up.

Ideal candidates for leadless pacemaker implantation include adult patients at high risk of lead-related complications and whose veins are being used for hemodialysis or chemotherapy. Others include those at high risk of infection from transvenous pacemakers, such as individuals with a history of endocarditis, septicemia, or lead extraction.^16,17 Here we identify a patient with intermittent CHB in whom traditional pacemaker implantation through subclavian venous access was limited due to vessel size.

Because the original Micra leadless device could only provide single-chamber ventricular pacing, its use was limited to <15% of pacemaker patients. Patients receiving ventricular single-lead pacemakers are primarily those with chronic atrial fibrillation and a slow ventricular response.¹⁸ With an algorithm that allows for detecting atrial contractions and ventricular synchrony, the Micra AV device represents a remarkable advancement over the original leadless pacemakers by providing AV synchronous pacing and expanding the patient pool to include those with AV block.^13,19 Enhancements have been made to the original algorithm to improve mode switching and to accommodate changes in patient rhythm and activity.²⁰ The patient described here, with CHB and poor subclavian access, represents an ideal candidate for these devices.

By preventing the complications associated with traditional pacemakers, leadless devices have become increasingly popular, especially with the advent of the Micra AV system. Recent analysis of the FDA database of major adverse clinical events associated with Micra implantation revealed that implantation of leadless Micra devices can be complicated by myocardial perforations that may lead to cardiac tamponade and death. While this risk is estimated to be <1%, leadless pacemaker implantation should involve informing patients of this risk and be performed in the setting of a hospital capable of performing emergency cardiothoracic surgery if complications arise.²¹

Vascular abnormalities may impede subclavian vein access for traditional pacemaker implantation. With the advent of the Micra AV leadless device, patients with second- and third-degree AV block and limited subclavian venous access can be effectively paced through a percutaneous femoral approach.

• Electrophysiology Lab Efficiency During the Treatment of Patients With Persistent Atrial Fibrillation: A Subanalysis of the STOP Persistent AF Study
• Transbasilic Approach for Percutaneous Closure of an Atrial Septal Defect
• Venovo Venous Stent in Treating Iliac Vein Compression: A Single-Center Experience
• Mechanisms of Lead Failure by Recall Status and Manufacturer: Results From the Pacemaker and Implantable Defibrillator Leads Survival Study (“PAIDLESS”)