Overcoming the Limitations of the DF-4 Defibrillator Connector

DOI: 10.19102/icrm.2013.040405

HOONG SERN LIM, MD, MRCP

University Hospital Birmingham NHS Trust, Edgbaston, Birmingham, UK

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ABSTRACT. The new DF-4 implantable defibrillator connector reduces the size of the device and facilitates lead connection to the device header. However, lack of connectivity of the DF-4 connector limits the possibility of additional shock coils in the event of high defibrillation energy requirements. This report describes the use of a new adaptor to overcome the problem of inadequate defibrillation safety margin in a patient implanted with a DF-4 implantable defibrillator connector.

KEYWORDS. defibrillation threshold, implantable cardioverter-defibrillator.

The authors report no conflicts of interest for the published content.
Manuscript received December 5, 2012, Final version accepted January 22, 2013.

Address correspondence to: Hoong Sern Lim, MD, MRCP. E-mail: hsern@doctors.net.uk

Introduction

A high defibrillation threshold has been reported in 3.9–12% of transvenous implantable cardioverter-defibrillator (ICD) systems.^1,2 Contemporary ICD pulse generators have a number of features specifically designed to improve defibrillation, including higher energy output, multiple programmable shock vectors, biphasic DF waveform, and adjustable pulse widths of the defibrillation waveform in some manufacturers. However, implantation of an extra defibrillator coil (via a DF-1 connector), such as an array in the dorsolateral chest wall, the coronary sinus, azygous vein, or within the pericardial space^3–5 is often required if these programmable options (and repositioning the defibrillator lead as appropriate) fail to overcome the high energy requirements for defibrillation.

The DF-4 connector is designed to facilitate lead-to-device connection, minimize the risk of incorrect device connection, and reduce the bulk of the device. Unfortunately, these advantages are achieved at the expense of additional connectivity, which precludes the latter strategy to overcome the problem of high DFT. This report describes the use of a new adaptor for additional DF-1 connectivity to overcome one of the limitations of the DF-4 connector.

Case

A 46-year-old man underwent implantation of a biventricular pacemaker/cardioverter-defibrillator (Medtronic Protecta, Minneapolis, MO) on the basis of left bundle branch block, ischemic heart disease with severe left ventricular (LV) dysfunction (ejection fraction 15–20%) and New York Heart Association class III heart failure symptoms (primary prevention). A dual-coil right ventricular (RV) lead with DF-4 connector (Medtronic 6937M) was positioned at the RV apex and the LV lead positioned in the posterolateral region. The patient was treated with bisoprolol but not amiodarone. The device was implanted in a left pre-pectoral pocket.

Ventricular fibrillation (VF) was induced using the shock-on-T technique. Defibrillation (RV coil as anode) was unsuccessful at 20 J and 35 J, and external biphasic defibrillation at 200 J was required. Arterial blood sampling showed no evidence of acidosis and normal electrolytes. There was no clinical or fluoroscopic evidence of pneumothorax. The RV lead position was satisfactory. However, as the SVC coil was positioned in the low superior vena cava (SVC)/right atrium (due to fixed coil separation), which may be unfavorable for ventricular defibrillation,⁶ repeat defibrillation testing was performed with the SVC coil turned off. The HV impedance with the SVC coil turned off was 62 ohms. The second defibrillation test produced the same results (i.e., failure to defibrillate at 35 J and an external 200 J rescue shock was required). Owing to the length of the procedure, the decision was made to close the wound with a plan to revise the system with the availability of the DF-4 adaptor.

The patient was readmitted about 4 weeks following initial implantation for defibrillation testing and the addition of a shock coil if required. Prior to system revision, repeat defibrillation testing (RV coil-can) was again unsuccessful at full output. Therefore, a shock coil (Medtronic 6937) was implanted in the azygous vein and connected to the device using a specialized Y-adaptor (Medtronic 5019 HV splitter). The adaptor has a DF-4 connector at one end that connects to the device DF-4 header, and two separate connections at the other end—one for the DF-4 (Medtronic 6937M) lead; and the other for the additional shock coil via a conventional DF-1 connection (Figure 1a–c). The connection for the DF-4 lead excludes the SVC coil (note only three conductors in the adaptor). The HV impedances were 55 and 45 ohms for the azygous and RV coils respectively. Defibrillation testing with the induction of VF by shock-on-T was successful at 25 J.

Discussion

This is the first report to describe the use of an adaptor specifically to overcome the lack of connectivity for the DF-4 connector to overcome the problem with high defibrillation energy requirements. The DF-4 connector offers a number of advantages, including a reduction in the risk of incorrect device connection and the bulk of the device. Unfortunately, these advantages are achieved at the expense of additional connectivity. In this case, high defibrillation energy requirement was confirmed on repeated testing, in the absence of potentially reversible causes, with and without the SVC coil and despite a satisfactory RV lead position. The ICD (Medtronic) did not offer the possibility of programming different pulse widths. On this basis, the implantation of an additional coil (e.g., in azygous vein) is generally recommended.^7,8

Defibrillator coils in the SVC may be associated with increased risks of venous stenosis and complications in the event of system extraction. A single-coil lead would be preferable in this case to minimize transvenous hardware; particularly as the SVC coil position was unfavorable and ineffective. Unfortunately, the DF-4 leads available at the time of implantation were dual-coil leads. Of note, the addition of a separate shock coil would have required the DF-4 adaptor (HV splitter) described in this case even with the use of a single coil DF-4 lead.

In a similar case reported by Cogert and colleagues,⁹ persistent failure to defibrillate necessitated the replacement of the DF-4 device and lead with a DF-1 device and lead, undoubtedly at significant expense. This case demonstrates the feasibility of using an adaptor specifically designed for additional DF-1 connectivity to overcome high defibrillation energy requirements, albeit at the cost of additional bulk to the defibrillator system. Finally, this adaptor does not overcome the other limitation of additional pace/sense lead, if required.

References

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