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Electrocardiography Presentation Electrocardiography 31650 Biomedical Engineering Kaj-Åge Henneberg Electrocardiography Plan Function of cardiovascular system Electrical activation of the heart Recording the ECG Arrhythmia Heart Rate detection methods Group Work The Heart as a Pump Internal View of Heart Pulmonary Circulation Arterial Circulation Venous Circulation Coronary Circulation Heart Valves Mitral valve: Left AV valve Tricuspid valve: Right AV valve Pulmonary valve Aortic valve Valve Sequence 1. Isovolumetric contraction period: Contraction of ventricles while all valves are closed. 2. Ejection period: Pulmonary and aortic valves open when the pressure in the ventricles exceed that in the lungs and aorta Inertia prolongs aortic valve open time Valve Sequence 3. Isovolumetric relaxation period: All valves are closed until the ventricular pressure drops below atrial pressure 4. Filling period: Rapid filling phase Slow filling phase (diastasis) Atrial contraction ~ 8% of filling Electrocardiography 10 min. Break Conduction System Cardiac Action Potentials Show overhead Pacemaker action potentials Propagated action potentials Ca induced plateau AP duration shortens as wave travels through the tissue types Refractory period Wave propagation Show isochrone overhead Elementary dipole source Mean dipole source = Heart Vector Autonomic Innervation Parasympathetic: Acetylcholine Right vagus nerve to SA node Left vagus nerve to AV node Sympathetic: Noradrenalin Nearly uniform innervation throughout the heart Both act simultaneously: Cutting both increases HR Transmitter actions Acetylcholine: Noradrenalin: Increased gK Reduced gK More negative Vm More positive Vm Longer prepotential Shorter prepotential Slower HR Faster HR Earlier repolarization Increased gCa Shorter AP duration Longer AP plateau Less Ca++ storage Increased CA++ Weaker contraction storage Stronger contraction Lead Vectors Left Arm Heart Vector Lead Vector Left Leg Lead Potentials VI = H*LI Right Arm Left Arm VII = H*LII VIII = H*LIII Left Leg ECG Standard Limb Leads Precordial Electrodes ECG Segments and Intervals Normal ECG Leads Electrocardiography 10 min Break Arrhythmia Abnormal ECG waveforms Atrial origin AV origin Ventricular origin Atrial Flutter Atrial Fibrillation Premature Atrial Contraction The ectopic P wave is often hidden in the ST-T wave of the preceeding beat Premature Junctional Complex Captures the atria retrograde and the ventricles antegrade Premature Ventricular Contractions Unifocal or multifocal Singles, couplets, triplets or salvos (4-6) PVC: Compensatory Pause Top: Normal Rhythm Middle: PVC Blocks next sinus impulse Next impulse arrives on time Bottom: PAC No compensating pause ”R on T” Phenomenon Vulnerable period R-on-T PVCs may be especially dangerous in an iscemic situation. Can lead to ventricular tachycardia or fibrillation Ventricular Tachycardia Ventricular Fibrillation No pumping action Fatal if not intervened by defibrillation Ischemia Reduced blood supply Elevated membrane resting potential Shorter AP Steady injury current Elevated or depressed ST-segment Concave and Convex ST segment ST Segment Depression ST Segment Sloping Wolf-Parkinson-White Syndrome Abnormal pathway for impulse conduction between atrium and ventricle Atria to ventricles Ventricles to atria Left Ventricular Hypertrophy Increased pump load Increased ventricular wall thickness Stronger electric sources Right Ventricular Hypertrophy Normal Electrical Axis 1. Find weakest lead axis 2. Find the two perpendiculars 3. Pick the one in agreement with the polarity of the other leads Axis pointing to the left 1. aVR is the weakest Perpendiculars: -60 or 120 deg. Negative leads II and III, so: -60 degree Axis pointing to the right 1. aVR is weakest Perpendiculars: -60 or 120 degrees Positive leads II and III, so 120 degrees Electrocardiography 10 min Break Monitoring Arrhythmia Two ECG leads Bandwidth: 0.03 – 150 Hz Sampling frequency: 500 Hz Point-by-point sampling Online dual-lead display Online R-wave detection Online R-R interval charting Arrhrythmia alarms R-R interval measurement 1. Bandpass filter: 5-15 Hz 2. Sum the square of lead signals 3. Lowpass filter the result ~6-8 Hz 4. Threshold the result 5. Calculate R-R intervals 6. Plot R-R intervals online 7. Calculate running average over 4-6 beats Alarm Criteria Sinus Bradycardia: RR > 1000 ms Sinus Tachycardia: RR < 600 ms Ventricular Fibril.: RR > 1500 ms Ventricular Tachycardia: < 500 ms Skipped Beat: RR(t) > 1.9 AR(t-1) AR: Average of last 4-6 RR intervals PVC Criteria 1. RR(t-1) < 0.9 AR(t-2) 2. RR(t-1) + RR(t) ~2 AR(t-2) 3. Rate > 10 per minute 4. Duration of QRS > 0.12 s ”R-on-T” Criteria 1. RR(t-1) < 0.33 AR(t-2) 2. RR(t-1) + RR(t) ~ 2 AR(t-2) 3. Duration of QRS > 0.12 s Electrocardiography Labview demo.
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