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 Weaker contraction Increased CA++ storage Stronger contraction
Lead Vectors Left Arm Heart Vector Lead Vector Left Leg
Lead Potentials Right Arm V I = H*L I Left Arm V II = H*L II V III = H*L III 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