New approach to cardiac resynchronisation therapy: CRT without left ventricular lead

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There are many risks and pitfalls with the current cardiac resynchronisation therapy devices which underscore the need for innovative approaches. Christopher V DeSimone and Samuel J Asirvatham, Mayo Clinic, Rochester, USA, write about a novel pacing lead (developed at Mayo Clinic by Asirvatham, Paul A Friedman, and Charles J Bruce) to help optimise pacing and synchronisation capabilities. Asirvatham spoke about this approach at the 12th International Dead Sea Symposium on Innovations in Cardiac Arrhythmias and Device Therapy (3–5 March 2014, Tel-Aviv, Israel).

By Christopher V DeSimone and Samuel J Asirvatham

Cardiac resynchronisation therapy typically requires the use of three transvenously placed pacing leads: right atrial, right ventricle, and left ventricle. However, there are many risks and pitfalls inherent in the current device systems which underscore the need for innovative approaches. The atrioventricular septum is an attractive site for successful pacing of the left ventricle because of its unique myocardial orientation (Torrent-Guasp F et al, J Thorac Cardiovasc Surg 2001; 122:389–392) stemming from cardiac development, electrically connecting the right atrium to the left ventricle. In addition to the luxury of this electrical connection, the atrioventricular septum provides an optimal pacing platform that is easy to access and has unique durability because the mitral valve attachment is higher up on the septum than the tricuspid valve. We have parlayed our knowledge of the detailed anatomy of the cardiac conduction system and myocardial fiber orientation to recent advances in intramyocardial lead pacing designs to mitigate issues associated with current pacing technologies:

Specificity for pacing site of interest

Standard device electrodes may cause an “antennae effect” resulting in unwanted over-sensing of electrical signals from neighboring cardiac chambers; this lack of specificity results in dyssynchronous pacing stimuli sent to the ventricle. By using a completely intra-myocardial design with closely spaced anode and cathode, the ability for sensing and pacing is more specific, occurs at lower thresholds, and without the stimulation of the phrenic nerve. (Asirvatham SJ et al, PACE 2007; 30:748–754).

Optimum site for pacing and deployment

Endocardial lead placement in the right ventricle for apical pacing poses the risk of tricuspid valve damage, increased tricuspid regurgitation, dyssynchronous ventricular contraction, and lead to ventricular dysfunction. Pacing from the atrioventricular septum does not involve crossing the tricuspid valve and has been shown to result in synchronous ventricular contraction and paced QRS morphology of normal duration (Henz BD et al, J Cardiovasc Electrophysiol 2009; 20:.1391-1397).

Limitations of coronary venous anatomy for optimum lead placement

Left ventricular lead placement can have inherent difficulties based on coronary venous anatomy and thus may limit optimum placement. Utilisation of a single intramyocardial lead at the atrioventricular septum does not require access of the coronary sinus, nor does the lead invade the left ventricle (Noheria A et al, J Cardiovasc Electrophysiol 2013; 24:1–6).

Investigational studies have shown that the atrioventricular septum is an ideal target to electrically stimulate a synchronised contraction of the left ventricle (Konecny T et al, Cardiovascular Revascularization Medicine 2013;14:137–138). Reiterations of this novel and patented lead design by altering the co-axial, parallel, and longitudinal designs of the bi-helical inner and outer electrodes surrounding an insulated central pin have shown improved performance. More recently, this novel lead has shown safety, durability, and efficacy in pacing from the atrioventricular septum in chronic canine studies.

Further investigations are ongoing to optimise pacing and synchronisation capabilities of this novel lead in chronic, large animal studies. The assessment of long-term safety and efficacy at the atrioventricular septum and sustained synchronous mechanical ventricular activation will be paramount to forming the basis to begin first in-human trials. Therefore, this innovative technology is bringing the field of cardiac electrophysiology closer to achieving the pinnacle of pacing therapy-physiologic stimulation of the left ventricle.

Tomas Konecny and Elisa Ebrille also collaborated in the study of this novel approach. The authors would like to acknowledge Biotronik for their collaboration.

A. Novel intra-myocardial pacing lead with internal central pin and bi-helical electrode coils in position used for deployment

B. Ilustration of four chamber view showing site of deployment of lead at the atrioventricular septum. This region is formed by a relatevely more ventricular insertion of the tricuspid valve and more atrial insertion of the mitral valve to the interventricular septum

Christopher V DeSimone is a cardiology fellow in the Division of Cardiovascular Diseases, Department of Medicine, Mayo Clinic, Rochester, USA.

Samuel J Asirvatham is a consultant in the Division of Cardiovascular Diseases, Department of Medicine, and Division of Pediatric Cardiology, Department of Pediatric and Adolescent Medicine, Mayo Clinic, Rochester, USA.

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