Utilizing the New Lumax 740 DX System for Complete AV Block

Case Description

The patient is a 71-year-old man with a cardiovascular history significant for hypertension, dyslipidemia, non-insulin-dependent diabetes mellitus, obesity, and multi-vessel coronary atherosclerosis status-post surgical revascularization (1993, 3 vessels: LIMA>LAD, SVG>RCA, SVG>OM2) and percutaneous intervention (2008, bare-metal stent to SVG>OM2), who presented with a two-week history of transient dizziness and progressive dyspnea on exertion. His medications included: rosuvastatin 40 mg daily, enalapril 10 mg daily, aspirin 325 mg daily, and metformin 1,000 mg twice daily without recent changes. He specifically denied chest discomfort, palpitation, orthopnea, paroxysmal nocturnal dyspnea, or syncope, but did endorse profound dizziness, especially upon standing, as well as exertional dyspnea that has been progressive over two weeks. Review of his prior diagnostic exams revealed stable hypertensive heart disease with concentric LVH and preserved biventricular function by echocardiography, without focal wall motion abnormalities; EKGs revealed sinus rhythm with an incomplete RBBB, without electrocardiographic signs of prior myocardial infarction. Nuclear imaging in 2012 was unremarkable for residual ischemia territories. 

Upon arrival in the office, intake exam was within normal limits and vital signs were stable. A screening EKG was obtained (Figure 1), which demonstrated sinus rhythm at 75 bpm, normal axis, complete AV block, incomplete RBBB with junctional rhythm at 45 bpm, and inferior ST-segment elevation with reciprocal anterolateral ST-segment depression consistent with inferior acute myocardial injury due to myocardial infarction. He was transferred immediately to the Cardiovascular Institute at NYU Langone Medical Center for diagnostic angiography and electrophysiology support; his presenting cardiac troponin I was 13, and angiography showed a 100% thrombotic occlusion of the proximal SVG>RCA graft for which he underwent aspiration and mechanical thrombectomy with distal protection filter, followed by stenting of the involved segment achieving TIMI 2 flow in the graft with 0% residual stenosis (Figures 2A and B). A temporary transvenous pacemaker wire was inserted and left in place following the intervention; it was programmed to backup VVI mode at 50 bpm. 

He was transitioned to the critical care unit for observation. The electrophysiology service was consulted regarding the need for a permanent pacemaker — at which time we discussed the natural history of AV block in the setting of acute inferior myocardial infarction — and continued observational management, with back-up pacing, was recommended. By hospital day 3, the patient remained in stable sinus rhythm with complete heart block, with a stable RBBB junctional escape of 50–60 bpm, and without significant ambient ectopy; he was exercised on the floor to demonstrate chronotropic competence of both his sinus and AV nodal escape, which remained intact. However, given no sign of conduction return in the setting of his complex atherosclerotic heart disease, the need for a permanent pacemaker system was discussed and recommended. Benefits, alternatives, and risks were reviewed in detail, with adequate time for focused questions and discussion with family and team members; however, the patient refused. This was revisited on hospital day 4, again in consultation with the patient’s family and cardiovascular care team; however, the patient remained adamant about “waiting it out.”

On hospital day 5, at 9:53 AM, despite the stable sinus and junctional rhythms, the patient suffered a PVC-initiated (R-on-T) polymorphic VT/VF arrest and required external defibrillation (x2) to resuscitate him from sudden cardiac death. (Figure 3) Following the event, he was stabilized, neurologically intact without signs of new ischemia, and ready to have a device implanted. After further discussion with the patient, care team, and family, the clinical decision was made to implant a single chamber implantable cardioverter-defibrillator (ICD) for the secondary prevention of sudden cardiac death with technology to allow for atrial sensing and ventricular pacing, as he had an intact sinus mechanism.

He underwent uneventful placement of the BIOTRONIK Lumax 740 VR-T DX system, with the Linox Smart S DX lead by single axillary puncture (Figures 4A and B). At implant, sensed atrial waves [2.7 mV] and ventricular waves [12.1 mV] were recorded via the program system analyzer (Figure 5); lead impedance measured 679 ohms with shock impedance of 67 ohms, with no diaphragmatic capture at 10V. Defibrillation threshold testing was performed by T-wave shock and successful at <20 joules. He was programmed to VDD mode 50–120 bpm, with tachytherapy zones to allow for VT monitoring >170 bpm and for VF therapy at >220 bpm, 20/30 interval detection, with ATP during charge and first shock at 30 J.

In the interval follow-up period of over one month, the patient’s atrial sensing remains excellent, averaging 3 mV, and he remains 100% V-paced, without new events. (Figure 6)

Discussion

This case illustrates the clinical application of a new iteration of technology that has been long known and understood, but recently improved upon: the integrated VDD lead. BIOTRONIK’s new DX system, consisting of the Lumax 740 VR-T Dx device and Linox Smart S Dx lead, allows for dual chamber diagnostics within a single implantable cardioverter-defibrillator (ICD) lead (Figure 7). The main purpose of a single pass dual chamber VDD ICD system is to improve the discrimination between atrial and ventricular tachyarrhythmias. We felt this platform was appropriate for our patient to enable atrial diagnostics and discrimination with less hardware exposure,¹ as he had demonstrated an intact and chronotropically competent sinus node with persistent AV block, also necessitating ventricular pacing. 

The clinical scenario in our patient is relatively rare with modern treatment of myocardial infarction, but highlights robust prior experience with inferior wall myocardial ischemia/infarction in the setting of significant multi-vessel coronary artery disease.² The right coronary artery supplies the SA node in 60% of people, and the left circumflex in the remaining. In over 90% of people, the RCA feeds the AV node and proximal His. The terminal portion of the His and main left bundle and right bundle branch are supplied by septal perforators of the LAD. Sinus bradycardia, prolonged PR conduction with Wenckebach, and complete heart block are common in inferior myocardial infarctions (IMI). Complete AV block occurs in approximately 10% of patients with IMI. This rarely occurs suddenly, most often seen with prolonged PR conduction gradually progressing to complete AV block. AV block occurs within the node in over 90% of cases and typically results in a transient block, likely due to heightened vagal tone; the escape complex is usually narrow and infrequently requires pacing, but this was clearly not the case with our patient, implicating the multi-vessel disease in perpetuating AV block.³ 

Universally, these clinical features portended a poor outcome following myocardial infarction⁴ and guidelines outline a Class I, level of evidence B indication for device implantation.⁵ With regard to selection of dual chamber versus single chamber for AV block, guidelines list desire for AV synchrony and limiting the number of pacing leads as factors in guiding VDD lead selection, driven by data showing that sequential AV pacing improves quality of life and functional endpoints.^6,7

The VDD lead concept is not new, with models available from all manufacturers over the past three decades for pacemaker leads; multiple studies have published stable atrial sensing ability amortized over timeframes out to three years with comparable rates of atrial sensing decline versus traditional dual chamber systems⁸; however, extension of this technology into the defibrillator system helps to address the need to delineate complex arrhythmias in cardiac patients at risk for sudden cardiac arrest.⁹ 

BIOTRONIK’s Linox S Dx lead atrial dipole has been optimized with 15 mm spacing and a larger 49 mm² surface area; it is based on the Linox 7.8 Fr, active fixation design which has over eight years of prior clinical observation time, without major recall or design issues to date. Coupled with the Lumax VR-T DX device with novel signal amplification and processing algorithm, atrial sensing ability has been shown to remain stable over a mid-term time course, maintaining a 96.5% atrial sensing accuracy.¹⁰ The addition of an atrial sensing mechanism also allows for incremental diagnostic accuracy (18–35%) in discrimination of potential ventricular arrhythmia, in comparison to single chamber electrograms; data which has been shown to lend prognostic evidence for significant cardiovascular events.^11,12 Other factors addressed by the integrated lead technology include reduced implant time, reduced procedure complication and mortality rates, and less physical hardware in the setting of potential future extraction, at potentially lower costs.^13,14 The lead has also been used in specialized clinical case scenarios, such as those with persistent left superior vena cava requiring ICD implantation.¹⁵ 

Limitations of the integrated system include the possibility of developing a future atrial pacing need, which would require implant of both a new atrial lead and a new generator system. The likelihood of this scenario remains very low, as large-scale ICD trials (including MVP, SCD-HeFT, and DAVID) have shown an average of 4% of patients developing a need for atrial pacing support, most of which could be minimized via programming configuration.¹⁶ The lead is also only available in a single coil configuration and therefore may not be suitable for potential high DFT candidates. Despite this fact, there is ongoing data to support the routine use of single coil leads in all implants,^17,18 and it has become our standard practice outside of extreme cases. As is the case for all dual chamber sensing ICD systems, far-field ventricular sensing through the atrial channel during tachyarrhythmias may also be observed and may lead to inappropriate tachycardia therapies or inhibition effective tachytherapies in ventricular arrhythmias. Prior study of this potential mechanism has revealed no significant differences to traditional dual chamber ICD systems and may be averted by appropriate programming, though direct head-to-head comparison studies between VDD and DDD systems are lacking.¹⁹ Finally, there is a potential for variable atrial sensing with marked changes in body positioning given the suspended positioning of the atrial dipole; it is recommended that the device be checked in multiple positions and with routine exercise activity post-implantation — the advent of home monitoring achieves this easily.

In conclusion, our case demonstrates the use of the new Lumax 740 DX system, highlighting the advantages of a dual chamber ICD system through a single pass VDD ICD lead and outlining further potential for this improved technology.  

Editor’s note: This article underwent peer review by one or more members of EP Lab Digest’s editorial board. 

Disclosure: Dr. Fowler reports payment for development of educational presentations including service on speakers’ bureaus (speaker at fellows teaching courses).  Dr. Chinitz reports payment for development of educational presentations including service on speakers’ bureaus (ACE Meetings: International Educational Symposia). 

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