George H Crossley (Nashville, USA) writes on the role of quadripolar leads in cardiac resynchronisation therapy to treat heart failure patients.
Cardiac resynchronisation therapy (CRT) is highly efficacious in treating heart failure in patients with moderate-to-severe heart failure and a prolonged QRS duration.1 The successful achievement of a stable and effective left ventricular (LV) lead position is the pivotal element of effective CRT.2
There are several variables that may hinder successful CRT outcomes. The lead must be put in a stable location or there will be no LV pacing. The best position for stability may well be different from the optimum location for pacing. It is common for the placement of the lead tip to either be apical or too close to the phrenic nerve but, in fact, the best location for pacing may be more proximal. It is also not infrequent that the operator will adequately test for phrenic nerve stimulation at the time of implantation, yet the patient develops phrenic nerve stimulation the next day he/she is up and about. This can happen because the lead is in a coronary vein and the phrenic nerve is attached to the parietal pericardium, an association that certainly changes with posture. Likewise, even with the most experienced operators, there is a finite risk of micro or macro lead dislodgment.
Until recently, operators often had to compromise lead position in favour of a stable position. Effective lead placement was limited by the availability of only unipolar and bipolar leads. The lead had to be put in a place where we could wedge it into the venous anatomy. Only recently, has a new option been available: quadripolar left ventricular leads.
The development of quadripolar leads opens an exciting new era in CRT. The physician is now liberated to balance the need for a stable lead position with the best pacing lead location, offering many more choices. For example, in Figure 1, the lead was lodged into a branch that had a great stimulation threshold of 0.6 volts on the distal electrode, but unfortunately had a phrenic nerve threshold of about 1.5 volts. Using the Attain Performa Model 4298 quadripolar lead (Medtronic), we were able to pace electrodes 2 and 3 (a narrow-spaced pair) with a myocardial stimulation threshold of 0.7 volts, with no phrenic nerve capture even at 8 volts.
There are currently two models of quadripolar leads available in the USA. St Jude Medical’s model has four evenly spaced electrodes attached to a pulse generator, which allows for 10 different vectors for pacing. The Medtronic Attain Performa Model 4298 is a quadripolar lead with 16 pacing vectors, designed with a wide spacing between electrodes 1 and 2 and between electrodes 3 and 4. Conversely, the spacing between electrodes 2 and 3 is narrow, creating a much smaller vector that significantly reduces the chance of phrenic nerve capture.
Another notable design difference between the two available leads is that each of the four electrodes on the Medtronic lead elutes steroid. This is likely to be responsible for the lower thresholds observed on electrodes 3 and 4 on the Medtronic lead. In the St Jude lead, the mean stimulation threshold on electrodes 3 and 4 was 2.9±2.4 volts and 4.6±2.5 volts at three months3. Notably, in both the Medtronic and the St Jude trials, electrode 4 was sometimes located in the coronary sinus.
Personally, I find CRT to be the most gratifying thing that we do in electrophysiology, especially as it relates to the improved quality of life for the patient. It is truly amazing to see a pale and slow patient transform into a pink and chipper patient with the addition of effective cardiac resynchronisation therapy. This new quadripolar lead technology certainly adds a very important tool to our armamentarium, allowing us to achieve this life improving and life sustaining therapy with a greater degree of certainty.
References
- Abraham WT, Fisher WG, Smith AL et al. Cardiac resynchronization in chronic heart failure. New England Journal of Medicine 2002;346(24):1845-1853.-
- Khan FZ, Virdee MS, Fynn SP, Dutka DP. Left ventricular lead placement in cardiac resynchronization therapy: where and how? [Review] [58 refs]. Europace 2009;11(5):554-561.
- George H Crossley III, Maurio Biffi, W Ben Johnson et al. A novel quadripolar lead with a narrow-spaced bipole allows for effective LV pacing while avoiding phrenic nerve stimulation – Attain Performa LV Lead study primary results. Circulation (in press). 11-1-2014. Ref Type: Abstract
George H Crossley is with Vanderbilt University Heart and Vascular Institute, Nashville, USA. He is consultant and speaker for Medtronic and Boston Scientific
