Leads and the Abnormal Heart

DOI: 10.19102/icrm.2015.060905

CHRISTOPHER J. MCLEOD, MD¹, PHILIP Y SUN, MSc², SAMUEL J ASIRVATHAM, MD^1,3

¹Division of Cardiovascular Diseases, Mayo Clinic, Rochester, MN

²Mayo Medical School, Mayo Clinic, Rochester, MN

³Department of Pediatrics and Adolescent Medicine, Mayo Clinic, Rochester, MN

The authors report no conflicts of interest for the published content.
Manuscript received August 20, 2015, final version accepted September 2, 2015.

Address correspondence to: Samuel J Asirvatham, MD, Division of Cardiovascular Diseases, Department of Medicine, Mayo Clinic College of Medicine, Department of Pediatrics and Adolescent Medicine, Mayo Clinic, Rochester, MN, 200 First Street SW, Rochester, MN 55905. E-mail: asirvatham.samuel@mayo.edu

The manuscript by Carlson et al, describing the prolapse of redundant pacemaker leads into the inferior vena cava with ensuing obstruction, illustrates an important concept in pediatric electrophysiology. Their case highlights the fact that somatic growth needs to be taken into account when implanting these leads, yet excessive redundancy can result in potentially catastrophic consequences for the patient. The case also illustrates how leads with this amount of redundancy, and prolapse within the hepatic venous system, can also be safely extracted before reimplantation of a new system. It would also be important for readers to know whether there was resolution in the hepatic dysfunction based on liver enzyme analyses or follow-up imaging, crucial to the care of this particular patient.

Equally germane to the discussion of implantation of a pacemaker in children with somatic growth ahead of them, however, is the route of access to the heart. Typically, an epicardial approach has been utilized, or pacing from an infraclavicular approach has been used with the leads reaching the heart via the superior vena cava (SVC). The decision to place a transvenous system versus an epicardial system is often a difficult one, and is based on the child’s size, age, indication for adjunctive surgery, and concomitant anatomical anomalies. In addition, in the absence of randomized clinical trials of cardiac pacing in pediatric patients, some centers may prefer an epicardial approach early on, so as to avoid the complications of intravascular leads. This approach, however, brings with it the risks associated with sternotomy or thoracotomy and is associated with a somewhat higher failure rate of epicardial leads (including those with steroid-eluting tips). This is likely due to a combination of somatic growth and the mechanical stresses placed on leads in a very active population of patients. The rare absence or (more commonly) occlusion of the SVC can negate a transvenous approach, and the operator may be obliged to utilize an epicardial approach. Persistence of the left superior vena cava (PLSVC) is also a relatively common congenital anomaly, present in around 0.4% of the general population but over 10% of patients with congenital heart disease.¹ The bilateral SVCs may or may not communicate with a bridging vein,² and this typically affects access to the heart for pacemaker lead placement.³

In this situation, the PLSVC poses two important technical challenges for the operator. The initial challenge is reaching the ventricle, atrium or coronary sinus via a dilated left SVC in patients who very often have other associated congenital anomalies. This frequently involves chamber dilatation, and approximation of the lead tip against the myocardial tissue of the right atrium or subpulmonic ventricle can be difficult. It has been our approach and that of other groups to use a coronary sinus (CS) delivery sheath for initial positioning of these leads. These standard CS guiding sheaths provide support and directionality for placement of the leads, which is otherwise especially difficult in this scenario. In situations where the subpulmonic atrioventricular valve should not be crossed, the CS can be considered, and this brings up the second challenge in pacing with varied anatomy such as a persistent SVC: that of lead stability. Placement of a lead in a dilated chamber or CS branch off a dilated left SVC often lacks the same support present in normal anatomy, and the operator does need to be vigilant in this regard.³

Given these difficulties in placing leads in patients with anatomical variations in the SVC, certain other innovative approaches could be considered in the future.^4,5 Crossing the tricuspid (or subpulmonic atrioventricular) valve can be avoided by placing a lead within the atrioventricular septum.⁴ This particular area of the heart separates the right atrium from the left ventricle, and there is evidence that a specially designed lead that crosses the atrioventricular septum permits depolarization of ventricular myocardium, even though the atrioventricular valve is not being crossed. Interestingly, myocardial electrical activation via atrioventricular septal pacing results in synchronous ventricular activation with early left ventricular free wall activation because of the unique spiral architecture of the left ventricle.^6–9 Another innovative method involves percutaneous epicardial pacemaker implantation, which may be of utility in the young patient when transvenous lead implantation in a standard manner via the SVC needs to be avoided.⁵ This particular strategy has been demonstrated to be successful in subxiphoid percutaneous placement of a specifically designed prototype lead using a technique of selective insulation over the epicardium of the heart. This has been shown to permit pacing without extracardiac stimulation or pain. Using a technique similar to that employed for epicardial cardiac ablation, this lead can potentially be delivered safely in this group of patients.

In summary, the reader needs to be aware of this potential complication employing excessive redundancy to address somatic growth in younger patients. Looking towards the future, there are innovations on the horizon that may alter the tools and approaches to permanent pacemaker implantation in this group. Furthermore, it is important for the operator to be aware of adjunctive techniques for delivery of atrial and ventricular leads in the patient with congenital anomalies of venous return to the heart.

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