While I’m pleased that items like fidget spinners have gone away, what happened to the other countless things that didn’t live up to the hype?
There were items such as the 3D TVs, Segways, Hoverboards, and moon shoes that seemed like a great idea at the time, but don’t get much attention now. On the big screen, Indiana Jones and the Kingdom of the Crystal Skull was released 19 years after the previous film in the franchise, Indiana Jones and the Last Crusade, but many fans and critics alike have named it one of the worst sequels ever made. Don’t get me started on the Game of Thrones finale after I had binge-watched all of the prior seasons within the couple months before the release.
Contact force is a popular phrase that has been going around in the ablation arena for the last several years and even more so recently. Is it living up to the hype?
Absolutely! This one has staying power.
So, what is contact force? To put it simply, it is measurable feedback that will tell the operator if their catheter tip is indeed touching the myocardium. During ablation we are looking to create a transmural lesion when possible. If a catheter is close to the tissue, but not touching, there may still be a large signal observed. However, the ablation performed will not create an effective lesion. For example, if you are grilling and merely hold your steak (or veggie burger) above the grates, you will not adequately cook the product. Once it has good contact with the grill grates, then the meat will begin to sear.
On the other side of the coin, contact force may also warn the operator of too much force. This could help prevent perforations and other complications.
At this time there are two different products with different technologies for contact force at this time. The SMARTTOUCH catheter by Biosense Webster utilizes a spring mechanism and the new Tacticath SE by Abbott which is based on light interferometry which is able to compute both magnitude and orientation of contact force.
The TOCCATA study identified the relationship between contact force (CF) and clinical outcomes during RF (radiofrequency) ablation of atrial fibrillation. This study was performed to determine the relationship between irrigated RF ablation with contact force and clinical recurrences. In this study, suboptimal catheter tip-to-tissue contact force is believed to reduce the clinical efficacy of RF lesion delivery. This study was a multicenter clinical trial with 34 patients. It was performed with the TactiCath irrigated RF ablation catheter. This catheter has a resolution and sensitivity of about 1 g. The sensor is able to measure both the lateral force and the axial force independently. The RF ablation power settings ranged from 15 to 40 W and no guidelines on contact force given. The saline irrigation flow was ≥ 2 mL/min during catheter manipulation, ≥ 17 mL/min during RF ablation for RF power of ≤ 30 W, and ≥ 30 mL/min for RF power > 30 W. Pulmonary vein isolation was verified by entrance block.
An average CF during ablation of < 10 g resulted in an AF recurrence rate of 100%. However, the recurrence rate dropped to 47% (or 53% success rate) when the average CF during ablation was between 10 and 20 g. The rate of success increased to 80% when the average CF during ablation was > 20 g.
There are some areas in the heart in which it is more challenging to obtain adequate contact force. Previous to contact force, the operator would be unaware that the lesion being created is not going to be effective long term. With CF information, the operator may now manipulate the catheter in such a way or use a steerable sheath to increase catheter tip-to-tissue contact. In areas in which it is still difficult to obtain the ideal force, the operator may then compensate by increasing the RF power and/or duration.
So yeah, it lives up to the hype and is widely accepted and utilized for many different ablation procedures today. Why would you want to fly blindly when there is a tool that will tell you if you are actually touching the tissue enough to create an effective lesion. As an adding side benefit, with good catheter tip-to-tissue contact, a more effective lesion will be created. The operator may then move on to the next ablation site sooner, decreasing procedure times. Win-Win.
Reference:
Reddy, V., Shah, D., Kautzner, J., et al. (2012, November). The relationship between contact force and clinical outcome during radiofrequency catheter ablation of atrial fibrillation in the TOCCATA study. Heart Rhythm, Vol 9, No 11.
This week’s EP question:
Which of the following does not correlate with the prolongation of phase 2 of the action potential?
- Increase in contractility strength
- Increase in conduction velocity
- Increase in contraction duration
- Increase in refractoriness
Answer
Increase in conduction velocity.
To change the conduction velocity of the cell, phase 0 will be altered. At steeper phase 0 will result in faster cell depolarization. The other three responses all correlate with the prolongation of phase 2 or the plateau phase.
