Too much, too little, or just right?: Applying the Goldilocks principle to cryoballoon ablation for atrial fibrillation

Abstract

Disclosure: None.A popular 19th century fairy tale involves a young girl named Goldilocks, who ventures out into the woods. She comes across a small cottage, knocks on the door, and finding it empty, enters. On a table in the kitchen, she encounters three bowls of porridge. She tastes each and finds that the first is too hot, the second too cold, and the third just right. Throughout the tale, she encounters may things in threes, all of which test the principle of finding something that is of just the right amount. This concept has become known as the Goldilocks Principle.When considering cryothermal balloon ablation for the treatment of atrial fibrillation (AF), applying the Goldilocks principle and finding the right amount of energy to deliver has been a challenge.Cryothermal balloon ablation is not alone in this challenge; this impacts all forms of ablation currently used. However, cryothermal ablation is unique as it can homogenize operator experiences and approaches and uses discrete time periods of energy delivery. As a favorable consequence of a more simplistic technical approach, the use of this technology can be promoted to achieve similar outcomes across a broad scope of operators. As a negative consequence, without a true understanding of the principle of too much, too little, or what is just right, untoward complications will predictably rise when excessive injury is delivered. The first-generation cryoballoon had nonhomogeneous balloon cooling with freezing primarily along the equator. In an early experience, 35 of 71 patients that underwent cryoballoon ablation for AF had recurrences of AF or tachycardia. In those patients with recurrence, 26 underwent a repeat electrophysiology study. Of the 97 pulmonary veins that were identified as treated, 67 (69%) had recurrent conduction. 1 Recurrences typically were found in inferior segments of the vein and were felt to reflect improper alignment of the balloon and an equatorial zone of cooling. Cryoballoon modifications including optimizing the flow of refrigerant, increasing the number of refrigerant jets within the balloon from four to eight, and positioning the jets closer to the distal balloon were made for improving thermal energy transfer to the tissue and circumferential cooling of the balloon including the tip region. 2 The device modifications favorably impacted the pulmonary vein recurrence rate in a comparative study of 206 patients, of whom 18 underwent a repeat electrophysiology study. In those that had a repeat procedure, 77% of the veins initially isolated with the second generation balloon were still isolated compared with 32% of those treated with the first generation balloon. 3 In another small comparative study of 56 repeat ablation patients between second generation cryoballoon ablation and force-sensing radiofrequency ablation, pulmonary vein recurrences were less in the cryoballoon group (36% vs 20%). 4The Goldilocks principle is in essence a "U" shaped curve paradigm.As the pendulum swings from that of "too little" toward "just right,"...