ThermoCool SmartTouch catheter for percutaneous radiofrequency ablation in atrial fibrillation

Introduction

Atrial fibrillation is the irregular and rapid beating of the upper 2 chambers of the heart (the atria), caused by the disruption of the electrical signals that control the heartbeat. In many cases of atrial fibrillation, extra electrical signals start in the area around the opening of the pulmonary veins (the large blood vessels that return blood from the lungs to the left atrium) causing the heart to beat erratically. It is 1 of the most common causes of abnormal heart rhythm with an estimated prevalence of 2% in England (Zoni‑Berisso et al. 2014). Atrial fibrillation is associated with a 4 to 5‑fold increase in the risk of stroke (British Heart Foundation 2015), and people with atrial fibrillation may be prescribed anticoagulants to minimise their risk of having a stroke (see the NICE guideline on the management of atrial fibrillation).

People with atrial fibrillation may be asymptomatic or experience symptoms such as palpitations, dizziness, breathlessness and fatigue (NHS Choices 2015). Atrial fibrillation can be classified as paroxysmal (an intermittent episode of atrial fibrillation which spontaneously terminates within 7 days, and usually within 48 hours), persistent (an episode lasting longer than 7 days) or permanent. Paroxysmal atrial fibrillation can progress to the permanent form (Jahangir et al. 2007).

Treatment options for atrial fibrillation include medication to control the rate or rhythm of the heart, or electrical cardioversion in which an electric current is used to restore a normal regular heart rhythm. Catheter ablation is recommended for patients when they cannot have drug therapy (January et al. 2014). It is used to block the erratic electrical signals. Pulmonary vein isolation (PVI) is the most commonly used catheter ablation technique. PVI is usually done using laser energy, radiofrequency energy or intense cold to ablate (destroy) a small area of tissue in the left atrium of the heart at the opening of the pulmonary veins. The resulting scar tissue prevents electrical signals originating from the cells within the pulmonary veins entering the heart. This process is conducted around the opening of the pulmonary veins. A mapping catheter positioned in each pulmonary vein is used to confirm entrance and exit block of the electrical signals after ablation. Pulmonary vein mapping and isolation is usually confirmed using a separate circular mapping catheter.

For PVI using ablation, clinicians must estimate the amount of contact force necessary to create effective scar tissue around the pulmonary veins. Failure to create durable scar tissue may allow the electrical signals to reconnect with the left atrium, which increases the likelihood of atrial fibrillation recurring (Neuzil et al. 2013). However, the application of too much force increases the risk of tissue injury or perforation of the wall of the heart, which can lead to serious complications. Catheters measuring real‑time contact force during ablation procedures provide clinicians with direct feedback and may improve both the efficacy and safety of ablation procedures (Gerstenfeld 2014).