Bio

Clinical Focus


  • defibrillators
  • atrial fibrillation
  • Arrhythmia
  • ventricular tachycardia
  • Cardiac Electrophysiology
  • cardiac resynchronization
  • Cardiovascular Medicine
  • Cardiology (Heart)
  • pacemakers
  • Clinical Cardiac Electrophysiology

Academic Appointments


Administrative Appointments


  • Clinic Advisory Council, Stanford Hospital and Clinics (2010 - Present)
  • Chief, Cardiology Clinics, Cardiovascular Medicine (2009 - Present)

Professional Education


  • Fellowship:Brigham and Women's Hospital Harvard Medical School (2005) MA
  • Fellowship:Brigham and Women's Hospital Harvard Medical School (2004) MA
  • Residency:Brigham and Women's Hospital Harvard Medical School (2001) MA
  • Internship:Brigham and Women's Hospital Harvard Medical School (1999) MA
  • Board Certification: Clinical Cardiac Electrophysiology, American Board of Internal Medicine (2007)
  • Board Certification: Cardiovascular Disease, American Board of Internal Medicine (2004)
  • Medical Education:Stanford University School of Medicine (1998) CA
  • PhD, Stanford University, Molecular Physiology (1998)
  • MD, Stanford University, Medicine (1998)

Research & Scholarship

Current Research and Scholarly Interests


(1) Mechanisms of Arrhythmia, including Ventricular Tachycardia, Atrial Fibrillation and other arrhythmias.
(2) New technologies and devices for catheter ablation.

Clinical Trials


  • THERMOCOOL® SMARTTOUCH™ Catheter for the Treatment of Symptomatic Paroxysmal Atrial Fibrillation CONTINUED ACCESS Not Recruiting

    This is a prospective, multicenter, non-randomized continued access clinical evaluation utilizing the THERMOCOOL® SMARTTOUCH™ catheter.

    Stanford is currently not accepting patients for this trial. For more information, please contact Paul Zei, (650) 723 - 7111.

    View full details

  • Catheter Ablation vs Anti-arrhythmic Drug Therapy for Atrial Fibrillation Trial Recruiting

    The (Catheter Ablation Versus Anti-arrhythmic Drug Therapy for Atrial Fibrillation Trial) CABANA Trial has the overall goal of establishing the appropriate roles for medical and ablative intervention for atrial fibrillation (AF). The CABANA Trial is designed to test the hypothesis that the treatment strategy of left atrial catheter ablation for the purpose of eliminating atrial fibrillation (AF) will be superior to current state-of-the-art therapy with either rate control or rhythm control drugs for decreasing the incidence of the composite endpoint of total mortality, disabling stroke, serious bleeding, or cardiac arrest in patients with untreated or incompletely treated AF.

    View full details

  • Attain Performa(TM) Quadripolar Lead Study Recruiting

    The purpose of the study is to evaluate the safety and efficacy of the Medtronic Attain Performa Quadripolar Leads (Model 4298, 4398, and 4598) during and post the implant procedure. This study will also assess the interactions of the Attain Performa leads with the entire Medtronic CRT-D system.

    View full details

  • THERMOCOOL® SMARTTOUCH™ Catheter for the Treatment of Symptomatic Paroxysmal Atrial Fibrillation Not Recruiting

    The purpose of this study is to demonstrate the safety and effectiveness of the THERMOCOOL® SMARTTOUCH™ Catheters with Contact Force Sensing Capability in the treatment of drug refractory symptomatic paroxysmal Atrial Fibrillation (AF) during standard electrophysiology mapping and RF procedures.

    Stanford is currently not accepting patients for this trial. For more information, please contact Linda Norton, RN, MSN, (650)725-5597.

    View full details

  • Use of the Hansen Medical System in Patients With Paroxysmal Atrial Fibrillation Recruiting

    The purpose of this study is to assess the safety and performance of the Hansen Medical Sensei Robotic System and Artisan Catheter when used to robotically manipulate the Biosense ThermoCool ablation catheter for the treatment of paroxysmal atrial fibrillation (irregular heartbeats originating in the upper chambers of the heart). The Biosense ThermoCool catheter is FDA approved for use in ablation therapy. The Hansen Medical Robotic Sensei System and Artisan catheter are approved in Europe for use during ablation procedures. This system has been used to treat atrial fibrillation in over 1000 patients worldwide by navigating existing, approved ablation catheters. In the US the Hansen Sensei System with Artisan catheter has FDA clearance as a robotic delivery system to facilitate manipulation, positioning and control of catheters used to collect electrophysiological data within the heart atria (upper chambers or the heart), but has not been studied or approved in the US for use in ablation treatment. This study is designed to evaluate safety, compatibility and effectiveness when the Hansen system is used with the ThermoCool ablation catheter in the treatment of paroxysmal atrial fibrillation. In this prospective,nonrandomized study, subjects will undergo treatment with robotic delivery of the of the ThermoCool ablation catheter. The primary effectiveness and safety outcomes must meet pre-established Target Performance Goals(chronic success rate is at least 54%; and, the major complication rate is no greater than 16%).

    View full details

Teaching

2013-14 Courses


Publications

Journal Articles


  • How insensitive ... How a mutation in the SCN5A voltage sensor leads to clinical arrhythmia HEART RHYTHM Zei, P. C., Caleshu, C. 2012; 9 (10): 1689-1690

    View details for DOI 10.1016/j.hrthm.2012.07.020

    View details for Web of Science ID 000309292600025

    View details for PubMedID 22841875

  • Incidence and clinical predictors of low defibrillation safety margin at time of implantable defibrillator implantation JOURNAL OF INTERVENTIONAL CARDIAC ELECTROPHYSIOLOGY Cheng, Z., Turakhia, M., Lo, R., Gupta, A., Zei, P. C., Hsia, H. H., Al-Ahmad, A., Wang, P. J. 2012; 34 (1): 93-100

    Abstract

    Determination of the defibrillation safety margin (DSM) is the most common method of testing device effectiveness at the time of implantation of implantable cardioverter defibrillator (ICD) or cardiac resynchronization therapy defibrillator (CRTD). Low DSM remains a problem in clinical practice.The purpose of this study is to ascertain the incidence and clinical predictors of low DSM and the treatment strategies for low DSM in ICD or CRTD recipients.Selected ICD or CRTD recipients from January 2006 to May 2008 who underwent DSM test at the time of implantation were included. Low DSM patients were defined as patients who had a DSM within 10 J of the maximum delivered energy of the device. These patients were compared to patients who had DSM?>?10 J.This study included 243 patients. Of these, 13 (5.3%) patients had low DSM, and 230 patients had adequate DSM. Patients with low DSM had a high prevalence of amiodarone use (69% vs 13%, p?

    View details for DOI 10.1007/s10840-011-9648-z

    View details for Web of Science ID 000303541200013

    View details for PubMedID 22391960

  • Electroanatomic localization of a slowly conducting atrioventricular (Mahaim) accessory pathway JOURNAL OF INTERVENTIONAL CARDIAC ELECTROPHYSIOLOGY Gupta, A., Hsia, H. H., Lo, R., Zei, P. C. 2011; 31 (2): 119-124

    Abstract

    We present a case of a 34-year-old female with Ebstein's anomaly and symptomatic wide complex tachyarrhythmia. Electrophysiologic evaluation demonstrated antidromic tachycardia utilizing a right-sided decremental, slowly conducting atrioventricular pathway. Distinct accessory pathway potentials along the length of the bypass tract were sequentially recorded to define the anatomic course of the pathway, as uniquely represented on a three-dimensional electroanatomic map, and to successfully guide catheter ablation.

    View details for DOI 10.1007/s10840-009-9440-5

    View details for Web of Science ID 000293026800003

    View details for PubMedID 19943099

  • Visualizing ablation gaps in vitro using a deflectable fiber optic endocardial visualization catheter JOURNAL OF INTERVENTIONAL CARDIAC ELECTROPHYSIOLOGY Irani, A. R., Lin, B., Eversull, C., Hsia, H. H., Zei, P. C., Wang, P. J., Al-Ahmad, A. 2009; 25 (2): 107-110

    Abstract

    The efficacy of pulmonary vein isolation for the treatment of atrial fibrillation may be limited by the ability to make continuous and transmural lesions utilizing an ablation catheter. Gaps often persist between ablation lesions leading to failed electrical isolation and thus failed ablation. Recently, a deflectable fiberoptic endocardial visualization catheter has been introduced for use in imaging the coronary sinus using light in the visible spectrum. We utilize this catheter to visualize the endocardial surface and examine radiofrequency ablation lesions in porcine endocardium to determine the presence of gaps between radiofrequency lesions.Videos were taken of the lesions and shown to two readers who were asked to identify the gaps ranging from less than 0.1 mm-9.8 mm.Ninety-four lesion gaps were reviewed. The readers demonstrated a combined accuracy of 98.4% at identifying gaps.Gaps between ablation lesions can be accurately identified down to less than 1 mm distances in vitro using a direct visualization catheter. Further studies are warranted to confirm these finding in vivo.

    View details for DOI 10.1007/s10840-008-9338-7

    View details for Web of Science ID 000267683500004

    View details for PubMedID 19148727

  • Direct Visualization of Cardiac Radiofrequency Ablation Lesions JOURNAL OF CARDIOVASCULAR TRANSLATIONAL RESEARCH Eversull, C. S., Lin, B., Irani, A. R., Quigley, M. L., Mourlas, N. J., Hsia, H. H., Zei, P. C., Al-Ahmad, A., Wang, P. J. 2009; 2 (2): 198-201

    Abstract

    Effective ablation of atrial fibrillation and other cardiac arrhythmias requires precise catheter navigation and controlled delivery of energy to cardiac tissue. In this study, we summarize our initial experience using a fiber optic direct visualization catheter to evaluate and guide placement of endocardial radiofrequency (RF) ablation lesions. RF lesions were created in cadaveric porcine hearts and examined in a blood-filled field using a direct visualization catheter. Direct visualization of RF lesions was repeated in vivo using an ovine model. Lesions and interlesion gaps were clearly identifiable using the direct visualization catheter. It was possible to place lesions in proximity to anatomical landmarks and in relation to one another. Catheter-generated images correlated well with lesion appearance on gross examination. Direct catheter-based visualization is a feasible technique for guiding RF lesion placement, estimating lesion size, and identifying interlesion gaps. Future work is needed to correlate surface appearance with transmurality and electrical isolation.

    View details for DOI 10.1007/s12265-009-9094-9

    View details for Web of Science ID 000284690100010

    View details for PubMedID 20559988

  • The Efficacy of Implantable Cardioverter-Defibrillators in Heart Transplant Recipients Results From a Multicenter Registry CIRCULATION-HEART FAILURE Tsai, V. W., Cooper, J., Garan, H., Natale, A., Ptaszek, L. M., Ellinor, P. T., Hickey, K., Downey, R., Zei, P., Hsia, H., Wang, P., Hunt, S., Haddad, F., Al-Ahmad, A. 2009; 2 (3): 197-201

    Abstract

    Sudden cardiac death among orthotopic heart transplant recipients is an important mechanism of death after cardiac transplantation. The role for implantable cardioverter-defibrillators (ICDs) in this population is not well established. This study sought to determine whether ICDs are effective in preventing sudden cardiac death in high-risk heart transplant recipients.We retrospectively analyzed the records of all orthotopic heart transplant patients who had ICD implantation between January 1995 and December 2005 at 5 heart transplant centers. Thirty-six patients were considered high risk for sudden cardiac death. The mean age at orthotopic heart transplant was 44+/-14 years, the majority being male (n=29). The mean age at ICD implantation was 52+/-14 years, whereas the average time from orthotopic heart transplant to ICD implant was 8 years +/-6 years. The main indications for ICD implantation were severe allograft vasculopathy (n=12), unexplained syncope (n=9), history of cardiac arrest (n=8), and severe left ventricular dysfunction (n=7). Twenty-two shocks were delivered to 10 patients (28%), of whom 8 (80%) received 12 appropriate shocks for either rapid ventricular tachycardia or ventricular fibrillation. The shocks were effective in terminating the ventricular arrhythmias in all cases. Three (8%) patients received 10 inappropriate shocks. Underlying allograft vasculopathy was present in 100% (8 of 8) of patients who received appropriate ICD therapy.Use of ICDs after heart transplantation may be appropriate in selected high-risk patients. Further studies are needed to establish an appropriate prevention strategy in this population.

    View details for DOI 10.1161/CIRCHEARTFAILURE.108.814525

    View details for Web of Science ID 000269161600007

    View details for PubMedID 19808340

  • Optimal Programming of ICDs for Prevention of Appropriate and Inappropriate Shocks. Current treatment options in cardiovascular medicine Lo, R., Al-Ahmad, A., Hsia, H., Zei, P. C., Wang, P. J. 2008; 10 (5): 408-416

    Abstract

    Expansion of indications for implantable cardioverter-defibrillators (ICDs) has led to a significant increase in the number of patients receiving ICDs and the number of lives saved because of ICD therapy. However, appropriate or inappropriate shocks are frequent and may result in a significant decrease in quality of life in patients with ICDs. Atrial fibrillation with rapid ventricular response, sinus tachycardia, atrial tachycardia or atrial flutter with rapid conduction, and other supraventricular tachycardias are the most common arrhythmias causing inappropriate therapy. Other causes include oversensing of diaphragmatic potentials or myopotentials, T-wave oversensing, double or triple counting of intracardiac signals, lead fractures or header connection problems, lead chatter or noise, and electromagnetic interference. Strategies to reduce inappropriate therapy using device programming rely on the ability to distinguish supraventricular and atrial arrhythmias from ventricular tachycardia. Avoiding therapy for nonsustained ventricular arrhythmias and increasing the role of antitachycardia pacing to terminate ventricular tachycardia are key approaches to reducing shocks for ventricular arrhythmias. Optimal programming holds great promise for decreasing the overall incidence of shock therapy and increasing ICD acceptance.

    View details for PubMedID 18814830

  • Time-resolved three-dimensional imaging of the left atrium and pulmonary veins in the interventional suite - A comparison between muttisweep gated rotational three-dimensional reconstructed fluoroscopy and multislice computed tomography HEART RHYTHM Al-Ahmad, A., Wigstroem, L., Sandner-Porkristl, D., Wang, P. J., Zei, P. C., Boese, J., Lauritsch, G., Moore, T., Chan, F., Fahrig, R. 2008; 5 (4): 513-519

    Abstract

    Cardiac computed tomography (CT) is commonly used to visualize left atrial (LA) anatomy for ablation of atrial fibrillation. We have developed a new imaging technique that allows acquisition and visualization of three-dimensional (3D) cardiac images in the catheter lab.We sought to compare LA and pulmonary vein (PV) dimensions acquired using gated multisweep rotational fluoroscopy (C-arm CT) system and multislice computed tomography (MSCT) in an in vivo porcine model.A Siemens AXIOM Artis dTA C-arm system (Siemens AG, Medical Solutions) was modified to allow acquisition of four bidirectional sweeps during synchronized acquisition of the electrocardiogram signal to allow retrospective gating. C-arm CT image volumes were then reconstructed. Gated MSCT (SOMATOM Sensation 16 and 64, Siemens AG, Medical Solutions) and C-arm CT images were acquired in six animals. The two main PV diameters were measured in orthogonal axes. LA volumes were calculated. C-arm CT measurements were compared with the MSCT measurements.The average PV diameters using the C-arm CT were 2.24 x 1.35 cm, versus 2.27 x 1.38 cm for CT. The average difference was 0.034 cm (1.9%) between the C-arm CT and standard CT. The average LA volume using MSCT was 49.1 +/- 12.7 cm(3), as compared with 51.0 +/- 8.7 cm(3) obtained by the C-arm CT. The average difference between the C-arm CT and the MSCT was 1.9 cm(3) (3.7%). There were no significant differences in either the PV or LA measurements.Visualization of 3D cardiac anatomy during ablation procedures is possible and highly accurate. The 3D cardiac reconstructions acquired during ablation procedures will be valuable for procedural planning and guidance.

    View details for DOI 10.1016/j.hrthm.2007.12.027

    View details for Web of Science ID 000254596600003

    View details for PubMedID 18362018

  • A Covariance-Based Algorithm: A Novel Technique for Rhythm Discrimination in ICDs 2008 30TH ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY, VOLS 1-8 Kamousi, B., Lin, B., Al-Ahmad, A., Hsia, H., Zei, P., Natale, A., Moss, A., Daubert, J., Zareba, W., Wang, P. 2008: 5478-5481

    Abstract

    Inappropriate shocks due to misclassification of supraventricular and ventricular arrhythmias remain a major problem in the care of patients with Implantable Cardioverter defibrillators (ICDs). In this study we have investigated the ability of a new covariance-based algorithm, to distinguish Ventricular Tachycardia from other rhythms such as Supraventricular Tachycardia. The proposed algorithm has a low computational demand and with a small adjustment is applicable on both single-chamber and dual-chamber ICDs. The results are promising and suggest that the new covariance-based algorithm may be an effective method for ICD rhythm classification and may decrease inappropriate shocks.

    View details for Web of Science ID 000262404503170

    View details for PubMedID 19163957

  • Characterization of human coronary sinus valves by direct visualization during biventricular pacemaker implantation PACE-PACING AND CLINICAL ELECTROPHYSIOLOGY Anh, D. J., Eversull, C. S., Chen, H. A., Mofrad, P., Mourlas, N. J., Mead, R. H., Zel, P. C., Hsia, H. H., Wang, P. J., Al-Ahmad, A. 2008; 31 (1): 78-82

    Abstract

    The precise reasons for failure to cannulate the coronary sinus during biventricular device implantation are unknown. Visualization of the coronary sinus ostium during electrophysiology procedures may enhance understanding of how unusual anatomy can affect successful cannulation of the coronary sinus.The aim of this study was to describe the morphology of valves at the coronary sinus ostium (CSO) visualized directly with an illuminated fiberoptic endoscope during implantation of biventricular devices.The coronary sinus anatomy of one hundred consecutive patients undergoing implantation of biventricular devices was investigated using a fiberoptic endocardial visualization catheter (EVC).The CSO was clearly visualized in 98 patients using the EVC. A Thebesian valve was seen in 54% of these. Almost all Thebesian valves were positioned at the inferior (61%) or posterior (33%) aspect of the CSO. Only six patients had Thebesian valves that covered more than 70% of the CSO, but all were successfully implanted with a transvenous left ventricular pacing lead after cannulating the coronary sinus under direct visualization.Over half of patients undergoing biventricular device implantation have identifiable Thebesian valves. Even valves covering the majority of the ostial area may be traversed using direct visualization and modern catheterization techniques.

    View details for Web of Science ID 000253373400015

    View details for PubMedID 18181913

  • Cardiac device infections complicated by erosion JOURNAL OF INTERVENTIONAL CARDIAC ELECTROPHYSIOLOGY Tsai, V., Chen, H., Hsia, H., Zei, P., Wang, P., Al-Ahmad, A. 2007; 19 (2): 133-137

    Abstract

    Implantation of pacemakers and implantable cardioverter-defibrillators (ICDs) can be complicated by infection and device erosion. It is unclear if the clinical features of patients who have device erosion differ from those without erosion.We retrospectively examined the records of all patients referred for explantation of a pacemaker or defibrillator from January 2000 to May 2005. We examined demographic variables including age, gender, and body mass index (BMI) as well as clinical variables related to erosion and procedural variables.Seventy-two patients with infected pacemakers or ICDs were identified. Of these cases, 30 (42%) developed infection complicated by erosion, of which 8/28 (29%) were related to ICDs, and 22/44 (50%) were related to pacemakers.Device erosion was significantly associated with the presence of a non-systemic infection as opposed to cases without erosion. This finding may have implications in the timing of device re-implantation.

    View details for DOI 10.1007/s10840-007-9143-8

    View details for Web of Science ID 000249009800008

    View details for PubMedID 17668305

  • Epicardial ablation of postinfarction ventricular tachycardia with an externally irrigated catheter in a patient with mechanical aortic and mitral valves HEART RHYTHM Anh, D. J., Hsia, H. H., Reitz, B., Zei, P. 2007; 4 (5): 651-654

    View details for DOI 10.1016/j.hrthm.2007.01.011

    View details for Web of Science ID 000246188800016

    View details for PubMedID 17467636

  • VF and fatal cardiac arrest following ICD therapy delivery: What is the cause? PACE-PACING AND CLINICAL ELECTROPHYSIOLOGY Mofrad, P. S., Ottoboni, L., Zei, P. C., Hsia, H. H., Wang, P. J., Amin-Al-Ahmad 2007; 30 (4): 551-553

    View details for Web of Science ID 000245642600018

    View details for PubMedID 17437582

  • Large radiofrequency ablation lesions can be created with a retractable infusion-needle catheter JOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY Sapp, J. L., Cooper, J. M., Zei, P., Stevenson, W. G. 2006; 17 (6): 657-661

    Abstract

    Radiofrequency (RF) catheter ablation of ventricular tachycardia is sometimes limited by inadequate lesion depth. We report the use of a novel retractable needle-tipped electrode catheter with intramyocardial (IM) saline infusion and IM RF energy delivery to create large myocardial ablation lesions.The left ventricle was entered via the femoral artery in 6 and 11 anesthetized goats and swine (32-90 kg) with an 8-F electrode catheter with an extendable 27-gauge needle at the tip (modified for RF ablation by making the needle electrically active). The needle was advanced 5-7 mm intramyocardially and 0.9% saline was infused 1 mL/min x 60 seconds prior to, and throughout a 120-second application of RF via the active needle, with power titrated to 12 W for 9 lesions, and 30-40 W for 37 lesions, followed by a 120-second RF application using the 4-mm-tip electrode, with power titrated to achieve a 10-Omega decrease in impedance. Needle/saline lesions were compared to 18 standard 4-mm-tip control lesions (power titrated to < or =50 W, to achieve a 10-Omega impedance decrease or limited to 60 degrees Celsius) and to 17 irrigated 3.5-mm-tip lesions (power titrated to < or =50 W, temperature limited to 50 degrees Celsius, 30 mL/min infusion rate). Lesions were identified in the excised heart, fixed, serially sectioned from the endocardium, and digitally analyzed to calculate volume.Lesions were homogeneous and had distinct borders. Compared to 4-mm-tip and irrigated-tip lesions, high-power needle/saline lesions were significantly deeper (13 +/- 2 vs 5 +/- 1 and 8 +/- 3 mm, P < 0.001), had significantly larger volumes (1,700 +/- 750 vs 240 +/- 170 and 750 +/- 650 mm(3), P < 0.001), and had larger cross-sectional area at each millimeter depth beyond the 1 mm (P < 0.01).IM saline infusion and IM RF energy delivery markedly increase RF lesion size as compared to standard RF ablation and is feasible with a percutaneous catheter. This method warrants further investigation because of its potential clinical utility.

    View details for DOI 10.1111/j.1540-8167.2006.00439.x

    View details for Web of Science ID 000237740000018

    View details for PubMedID 16836718

  • Modified temporary cardiac pacing using transvenous active fixation leads and external re-sterilized pulse generators JOURNAL OF THE AMERICAN COLLEGE OF CARDIOLOGY Zei, P. C., Eckart, R. E., Epstein, L. M. 2006; 47 (7): 1487-1489

    View details for DOI 10.1016/j.jacc.2006.01.006

    View details for Web of Science ID 000236647200027

    View details for PubMedID 16580542

  • Epicardial catheter mapping and ablation of ventricular tachycardia HEART RHYTHM Zei, P. C., Stevenson, W. G. 2006; 3 (3): 360-363

    Abstract

    Percutaneous entry into the pericardial space allows epicardial catheter mapping and ablation in the electrophysiology laboratory, opening a perspective on cardiac electrophysiology that previously was limited largely to the operating room. Scar-related reentry after myocardial infarction usually involves the subendocardium but in some patients can only be ablated from the epicardium. Epicardial, scar-related reentry also is an important cause of ventricular tachycardia in nonischemic cardiomyopathies. Rare supraventricular tachycardias and idiopathic ventricular tachycardia that cannot be defined from the endocardium sometimes can be ablated from the epicardium. With appropriate precautions the procedural risks are low. Epicardial catheter techniques expand the options for investigating cardiac electrophysiology and treating arrhythmias in humans and may lead to insights into transmural properties influencing repolarization and the genesis of arrhythmias.

    View details for DOI 10.1016/j.hrthm.2005.10.022

    View details for Web of Science ID 000235779600020

    View details for PubMedID 16500312

  • Voltage-dependent gating of single wild-type and S4 mutant KAT1 inward rectifier potassium channels JOURNAL OF GENERAL PHYSIOLOGY Zei, P. C., Aldrich, R. W. 1998; 112 (6): 679-713

    Abstract

    The voltage-dependent gating mechanism of KAT1 inward rectifier potassium channels was studied using single channel current recordings from Xenopus oocytes injected with KAT1 mRNA. The inward rectification properties of KAT1 result from an intrinsic gating mechanism in the KAT1 channel protein, not from pore block by an extrinsic cation species. KAT1 channels activate with hyperpolarizing potentials from -110 through -190 mV with a slow voltage-dependent time course. Transitions before first opening are voltage dependent and account for much of the voltage dependence of activation, while transitions after first opening are only slightly voltage dependent. Using burst analysis, transitions near the open state were analyzed in detail. A kinetic model with multiple closed states before first opening, a single open state, a single closed state after first opening, and a closed-state inactivation pathway accurately describes the single channel and macroscopic data. Two mutations neutralizing charged residues in the S4 region (R177Q and R176L) were introduced, and their effects on single channel gating properties were examined. Both mutations resulted in depolarizing shifts in the steady state conductance-voltage relationship, shortened first latencies to opening, decreased probability of terminating bursts, and increased burst durations. These effects on gating were well described by changes in the rate constants in the kinetic model describing KAT1 channel gating. All transitions before the open state were affected by the mutations, while the transitions after the open state were unaffected, implying that the S4 region contributes to the early steps in gating for KAT1 channels.

    View details for Web of Science ID 000077357400003

    View details for PubMedID 9834140

Conference Proceedings


  • A New Approach for ICD Rhythm Classification based on Support Vector Machines Kamousi, B., Tewfik, A., Lin, B., Al-Ahmad, A., Hsia, H., Zei, P., Wang, P. IEEE. 2009: 2478-2481

    Abstract

    Inappropriate shocks due to misclassification of supraventricular and ventricular arrhythmias remain a major problem in the care of patients with Implantable Cardioverter Defibrillators (ICDs). The purpose of this study was to investigate the ability of a new covariance-based support vector machine classifier, to distinguish ventricular tachycardia from other rhythms such as supraventricular tachycardia. The proposed algorithm is applicable on both single and dual chamber ICDs and has a low computational demand. The results demonstrate that suggested algorithm has considerable promise and merits further investigation.

    View details for Web of Science ID 000280543601357

    View details for PubMedID 19964965

  • Effects on ion permeation with hydrophobic substitutions at a residue in shaker S6 that interacts with a signature sequence amino acid Zei, P. C., Ogielska, E. M., Hoshi, T., Aldrich, R. W. NEW YORK ACAD SCIENCES. 1999: 458-464

    View details for Web of Science ID 000081584300046

    View details for PubMedID 10414322

Stanford Medicine Resources: