PSST 10819_11/2008 Arrhythmia in Practice Today ™ Content provided by Boston Scientific September 2008 Lessons in Lesions

PSST 10819_11/2008 Content provided by Boston Scientific September 2008 Arrhythmia in Practice Today™ Content provided by Boston Scientific September 2008 Objectives  Controlable/un-controlable  How does cooling impact lesion size and safety?  How does power affect lesions size and safety?  How does catheter tip size affect lesion formation?  Relation between catheter tip temperature and tissue temperature  Char and thrombus formation  Affects of contact on lesion formation What does this 1 st bullet mean? It seems incomplete

PSST 10819_11/2008 Content provided by Boston Scientific September 2008 Arrhythmia in Practice Today™ Content provided by Boston Scientific September 2008 Discovery of Cardiac Ablation Lesion Science 3 Severe complications related to DC ablation led to the search for an alternative energy source First “accidental” ablation with DC (direct current) energy TODAY First radiofrequency (RF) ablation in humans First DC ablation in a human

PSST 10819_11/2008 Content provided by Boston Scientific September 2008 Arrhythmia in Practice Today™ Content provided by Boston Scientific September 2008 Radiofrequency (RF) energy Improved energy form for ablation Localized thermal effect on the tissue No muscle stimulation Lesion Science 4 Alternating electrical current (AC) at a frequency of 500kHz similar to commercial 50 Hz

PSST 10819_11/2008 Content provided by Boston Scientific September 2008 Arrhythmia in Practice Today™ Content provided by Boston Scientific September 2008 Goals of Cardiac Ablation Selective neutralization of tissue within the heart that causes or helps to sustain an arrhythmia Apply sufficient energy to cause thermal injury and turn electrically active cardiac tissue into electrically inactive scar tissue (lesion) Tissue temperature of >50°C is required for lesion formation Understanding lesion science helps the clinician to deliver optimal therapy and may ultimately improve patient outcomes Lesion Science These 2 seem to say the same thing

PSST 10819_11/2008 Content provided by Boston Scientific September 2008 Arrhythmia in Practice Today™ Content provided by Boston Scientific September 2008 Success Factors Lesion Science 6 Successful Cardiac Ablation Understand cardiac anatomy and structures Optimal catheter placement Deliver appropriate amount of energy to tissue Know when you’re done Avoid complications

PSST 10819_11/2008 Content provided by Boston Scientific September 2008 Arrhythmia in Practice Today™ Content provided by Boston Scientific September 2008 Resistive Heating: the light bulb analogy Light BulbRF Ablation Lesion Science 7

PSST 10819_11/2008 Content provided by Boston Scientific September 2008 Arrhythmia in Practice Today™ Content provided by Boston Scientific September 2008 The RF energy delivery circuit Closed loop electrical circuit catheter heart tissue dispersive electrode generator Lesion Science 8

PSST 10819_11/2008 Content provided by Boston Scientific September 2008 Arrhythmia in Practice Today™ Content provided by Boston Scientific September 2008 Resistive heating RF current is delivered via the catheter tip INTO the tissue Because tissue has a very high resistance, the passage of current generates heat in the tissue Haines, DE et. al. : Pacing Clinical Electrophysiol : Haines D. The Biophysics of Radiofrequency Catheter Ablation in the Heart. PACE Vol 16, Part II, March 1993; RF ablation is NOT burning with a hot tip! Blood Tissue Lesion Science 9

PSST 10819_11/2008 Content provided by Boston Scientific September 2008 Arrhythmia in Practice Today™ Content provided by Boston Scientific September 2008 Conductive Heating Haines, DE et. al. : Pacing Clinical Electrophysiol : Haines D. The Biophysics of Radiofrequency Catheter Ablation in the Heart. PACE Vol 16, Part II, March 1993; Strickberger SA, Hummel J, Gallagher M, et al.” Effect of accessory pathway location on the efficiency of heating during RF catheter ablation. AM Heart J 129: Blood Tissue Heat conducted from warm electrode into cooler blood Heat conducted from warm tissue into cooler blood Heat conducted from resistively heated tissue into catheter tip Catheter tip heats up Lesion Science 10 Heat conducted from resistively heated tissue into surrounding tissue, expanding lesion

PSST 10819_11/2008 Content provided by Boston Scientific September 2008 Arrhythmia in Practice Today™ Content provided by Boston Scientific September 2008 Blood Tissue Heat conducted from warm catheter tip into cooler blood Heat conducted from warm tissue into cooler blood Heat conducted from resistively heated tissue into catheter tip Heat conducted from resistively heated tissue into surrounding tissue, expanding lesion Catheter tip heats up Convective Cooling Haines, DE et. al. : Pacing Clinical Electrophysiol : Haines D. The Biophysics of Radiofrequency Catheter Ablation in the Heart. PACE Vol 16, Part II, March 1993; Strickberger SA, Hummel J, Gallagher M, et al.” Effect of accessory pathway location on the efficiency of heating during RF catheter ablation. AM Heart J 129: Convective Cooling via (37°C) Blood Flow Lesion Science 11

PSST 10819_11/2008 Content provided by Boston Scientific September 2008 Arrhythmia in Practice Today™ Content provided by Boston Scientific September 2008 Power vs Temperature Control

PSST 10819_11/2008 Content provided by Boston Scientific September 2008 Arrhythmia in Practice Today™ Content provided by Boston Scientific September 2008 Tip Tissue Temperatures

PSST 10819_11/2008 Content provided by Boston Scientific September 2008 Arrhythmia in Practice Today™ Content provided by Boston Scientific September 2008 Tip Size

PSST 10819_11/2008 Content provided by Boston Scientific September 2008 Arrhythmia in Practice Today™ Content provided by Boston Scientific September 2008 Cooled Ablation

PSST 10819_11/2008 Content provided by Boston Scientific September 2008 Arrhythmia in Practice Today™ Content provided by Boston Scientific September 2008 Flow Rates

PSST 10819_11/2008 Content provided by Boston Scientific September 2008 Arrhythmia in Practice Today™ Content provided by Boston Scientific September 2008 Electrode to Tissue Contact

PSST 10819_11/2008 Content provided by Boston Scientific September 2008 Arrhythmia in Practice Today™ Content provided by Boston Scientific September 2008 Lesion Science Multiple Factors Influence Lesion Size & Quality: RF Power Delivered to the Targeted Tissue Duration Blood Flow Over the Tip/Tissue Interface Electrode Geometry* Electrode Tip/Tissue Contact* Type of Tissue Tip Orientation to the Tissue * Effected by Catheter Engineering

PSST 10819_11/2008 Content provided by Boston Scientific September 2008 Arrhythmia in Practice Today™ Content provided by Boston Scientific September 2008 Lesion Growth with Time Lesion Size (mm) Time (sec) Steady State = MAXIMUM Lesion Size heat generated within lesion = heat transferred away from lesion Haines D. Biophysics of Radiofrequency Lesion Formation. Catheter Ablation of Cardiac Arrhythmias (2006) ~1/2 max lesion size created in the first 5-10 seconds of energy delivery Lesion Science 19

PSST 10819_11/2008 Content provided by Boston Scientific September 2008 Arrhythmia in Practice Today™ Content provided by Boston Scientific September 2008 Temperature pattern within a lesion Lesion Science 20 Conductive Heating Convective Cooling

PSST 10819_11/2008 Content provided by Boston Scientific September 2008 Arrhythmia in Practice Today™ Content provided by Boston Scientific September 2008 Consequences of overheating Heat is conducted to the catheter tip and deeper tissue Catheter tip heats up; Surrounding blood is heated and coagulates Coagulum forms and adheres to the catheter tip Flow of current from the catheter tip to tissue is impeded System impedance rapidly increases Power delivery is terminated Resistive heat is generated in the tissue as current flows through it RF power is delivered Blood becomes denatured Lesion Science 21

PSST 10819_11/2008 Content provided by Boston Scientific September 2008 Arrhythmia in Practice Today™ Content provided by Boston Scientific September 2008 Consequences of overheating Heat is conducted to the catheter tip and deeper tissue Excess power delivery causes tissue overheating Power delivery is not terminated automatically and must be terminated manually Resistive heat is generated in the tissue as current flows through it RF power is delivered Vaporization of fluid causes steam pops and risk of rupture Lesion Science 22 Add a video of steam pop

PSST 10819_11/2008 Content provided by Boston Scientific September 2008 Arrhythmia in Practice Today™ Content provided by Boston Scientific September 2008 Impedance rise associated with high temp Haines D: Biophysics of Ablation: Application to Technology. J Cardiovasc Electrophysiol 2004; 15:S2-S11 Lesion Science 23

PSST 10819_11/2008 Content provided by Boston Scientific September 2008 Arrhythmia in Practice Today™ Content provided by Boston Scientific September 2008 Consequence of excessive intramural heating Normal Lesion Thiagalingam A, D’Avila A, McPherson C, Malchano Z, Ruskin J, Reddy V. Impedance and Temperature Monitoring Improve the Safety of Closed-Loop Irrigated-Tip RF Ablation. J Card Electrophysiol 18:3: , Lesion with Steam Pop Lesion Science 24

PSST 10819_11/2008 Content provided by Boston Scientific September 2008 Arrhythmia in Practice Today™ Content provided by Boston Scientific September 2008 Key points of lesion science Radiofrequency (RF) energy causes thermal lesion formation through resistive heating of myocardial tissue. Catheters are NOT a branding irons! The catheter tip gets hot ONLY because of its close proximity to the heated tissue. Heat is transferred to deeper layers of tissue (and the tip electrode and surrounding blood pool) via thermal conduction Tissue temperatures of >50°C or higher are required for lesion formation Lesion Science 25

PSST 10819_11/2008 Content provided by Boston Scientific September 2008 Arrhythmia in Practice Today™ Content provided by Boston Scientific September 2008 Key points of lesion science Blood flow cools the electrode tip and tip/tissue interface through convective cooling – the major factor opposing thermal conduction/lesion formation The hottest spot in a lesion is below the tissue surface Excessive heating (>100°C) at the tip/tissue interface causes coagulum formation, resulting in a system impedance rise, limiting RF delivery Buildup of intramural gases, due to excessive heating, accompanied by continued RF delivery may cause a “steam pop” Lesion Science 26

PSST 10819_11/2008 Content provided by Boston Scientific September 2008 Arrhythmia in Practice Today™ Content provided by Boston Scientific September 2008 Conclusion RF energy is the primary technology used in cardiac ablation –high success rates –low complication rates –easy to use Monitoring of tip electrode temperature may help prevent coagulum formation and steam pops Ultimately, lesion size is directly proportional to tissue heating Lesion Science 27

PSST 10819_11/2008 Content provided by Boston Scientific September 2008 Arrhythmia in Practice Today™ Content provided by Boston Scientific September 2008 Conclusion But, many factors influence tissue heating –RF power level and duration of delivery –blood flow over the electrode-tissue interface –catheter tip geometry –catheter tip/tissue contact Understanding lesion science allows delivery of optimal therapy and may ultimately improve patient outcomes Lesion Science 28