Schuessler Lecture - Understanding and Treating Atrial...

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Unformatted text preview: 9/20/2010 Understanding and Treating Atrial Fibrillation Richard B. Schuessler PhD Cardiothoracic Research Laboratory Outline Review of action potential and the ECG. How activation spreads in the atria. How we map the spread of the th activation. activation. How do these methods and data relate to the diagnosis and treatment of atrial fibrillation. Normal Heart Function Sinoatrial Node Normal Heart Function Atrioventricular Node 1 9/20/2010 Normal Heart Function Normal Heart Function Bundle of HIS Normal Heart Function Normal Heart Function Left Bundle Branch (LBB) Posterior Fascicle of LBB Anterior Fascicle of LBB Right Bundle Branch (RBB) Normal Heart Function Intervals Are Expressed in Milliseconds Purkinje Fibers 2 9/20/2010 How does activation propagate in the atria? How can we determine when activation occurs? Action potentials can be recorded in single cells or small pieces of isolated tissue. However, it is impractical to record it action action potentials in whole organs. The solution is to record extracellular extracellular potentials. How do we do this? Recording an extracellular potential The current flowing across the cellular membrane generates an extracellular potential Φe. 3 9/20/2010 Action Potential-Extracellular PotentialPotential How does this help us understand and treat understand and treat disease? disease? 4 9/20/2010 Prevalence Approximately 2.5 million people in the US suffer from AF Negative Sequelae of AF Loss of Rate Control and Regular Rhythm. Loss of atrial contribution to cardiac output. Increased risk of thromboembolism. 5 9/20/2010 Atrial Fibrillation How do we record and analyze these data in patients in the operating patients in the operating room room during open heart surgery? Cox Maze IV PO S T R A RPV PO ST LA LA SCV ANT RA & LA RPV LPV SVC LPV RAA RAA LAA LAA IVC IVC RV LV Normal Sinus Rhythm Freedom from AF All Patients 93% 6 9/20/2010 CT Scan Protocol: Surface Reconstruction Limitations of Present Procedure In some patients the Maze procedure is not enough to ablate AF. In other patients there are too many lesions lesions. If we understood an individual patients AF, then we can design a patient specific procedure. What do we know about the mechanisms causing AF? AF is maintained by reentry. depends upon the refractory period, the conduction velocity, and the the surface area. Can we estimate the “critical surface area” needed to maintain reentry? Reentry Surfaces are created by smoothing out distances between traced lines Estimate CV and ERP Calculate conduction velocity from activation sequence The minimal AF cycle length provides an an accurate estimation of the ERP Kim et al. “Relationship Between Local Atrial Fibrillation Interval and Refractory Period in the Isolated Canine Atrium.” Circulation. 1996;94:2961-2967. AF Model Solution to Critical Area Equation: =(ln (Pr[AF]/(1Acrit=(ln (Pr[AF]/(1-Pr[AF])) –a0 – a1(CV*ERP))/a2 CV = conduction velocity ERP = effective refractory period a0, a1, a2 are derived constants Pr[AF] = probability of sustaining AF How do we apply this to an intact heart? Specifically, how do you determine areas, conduction velocities, and refractory period? 7 9/20/2010 Algorithm Inverse Inverse Problem Calculate Surface area from CT. Estimate ERP from average cycle length of AF. Calculate average wave front velocities. velocities. Calculate critical area for AF. Subdivide atria below the critical area. Problems of Intraoperative Mapping Methods Analysis of electrograms recorded from multiple sites during surgery can take long periods to analyze. A patient’s arrhythmia during open heart heart surgery may not be the clinical AF. Limited time during a procedure to record and analyze data. Solution – ECG Imaging Animation of Activation - AF Can we map AF non-invasively? non We can record extracellular potentials from the body surface. Surface ECG’s can be related to the ECG’ th heart heart potentials by solving the inverse inverse problem. Technique developed by Dr Yoram Rudy. 8 9/20/2010 Thank you for your time! Questions? 9 ...
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This note was uploaded on 02/14/2012 for the course NUBITRY 3304 taught by Professor Various during the Spring '01 term at Albertus Magnus.

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