Real-time contact force measurement: a key parameter for controlling lesion creation with radiofrequency energy.

R adiofrequency (RF) energy, the dominant energy source for the treatment of various arrhythmias by catheter abla-tion, has replaced most other treatments for the effective suppression of supraventricular and ventricular arrhythmias. 1 With expanding indications, it has become increasingly clear that the success and sustainable effect of RF ablation depends on a critical understanding of the biophysics of lesion creation and its control. RF current at the electrode tissue (ET) interface is the key to RF lesion creation by virtue of its tissue heating capability 2 but cannot be measured directly, and therefore, delivered RF power and duration are typically manipulated to control lesion creation. 3 Despite such manipulation , there is significant variability in lesion size, which is thought to be responsible for both inefficacy and complications. Contact between electrode and tissue may be the key parameter to control lesion size because it is essential for the passage of current into the target tissue, but has until recently remained intangible and unmeasurable. RF energy delivery creates tissue coagulation and necrosis by producing targeted tissue hyperthermia. This hyperthermia is the consequence of resistive heating of a thin rim of tissue in direct contact with the RF energy delivering electrode, with surrounding tissue being heated by conduction. Direct resis-tive heating is produced by a high density of alternating current , the magnitude of which declines with the inverse of the square of the distance; therefore, target tissue contact is essential for effective lesion formation. 3 The key to effective and safe treatment with RF catheter ablation is controlling lesion size, that is, increasing or decreasing lesion size as desired. Precise control of lesion size is particularly important for treatment strategies requiring multiple coalescent ablations, for example, linear lesions making strategies, such as for atrial flutter, atrial fibrillation (AF), and reentrant ventricular tachy-cardia. 4 The real-time measurement of ET contact may be an effective lesion size controlling parameter in the absence of direct measures of tissue interface current or tissue temperature distribution. ET contact can be considered to have 2 components: the magnitude of the surface area of the electrode in direct contact with tissue (contact footprint) as well as its stability. Normal cardiac tissue like other soft tissue is both compliant and elastic: pushing a catheter in contact with tissue embeds the metal electrode tip progressively so that a greater percentage of the electrode surface is in direct contact with the …