Electrocardiography Biomedical Engineering Kaj-Åge Henneberg

Transcription

1 Electrocardiography Biomedical Engineering Kaj-Åge Henneberg

2 Electrocardiography Plan Function of cardiovascular system Electrical activation of the heart Recording the ECG Arrhythmia Heart Rate detection methods Group Work

3 The Heart as a Pump

4 Internal View of Heart

5 Pulmonary Circulation

6 Arterial Circulation

7 Venous Circulation

8 Coronary Circulation

9 Heart Valves Mitral valve: Left AV valve Tricuspid valve: Right AV valve Pulmonary valve Aortic valve

10 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

11 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

12 Electrocardiography 10 min. Break

13 Conduction System

14 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

15 Wave propagation Show isochrone overhead Elementary dipole source Mean dipole source = Heart Vector

16 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

17 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

18 Lead Vectors Left Arm Heart Vector Lead Vector Left Leg

19 Lead Potentials Right Arm V I = H*L I Left Arm V II = H*L II V III = H*L III Left Leg

20 ECG Standard Limb Leads

21 Precordial Electrodes

22 ECG Segments and Intervals

23 Normal ECG Leads

24 Electrocardiography 10 min Break

25 Arrhythmia Abnormal ECG waveforms Atrial origin AV origin Ventricular origin

26 Atrial Flutter

27 Atrial Fibrillation

28 Premature Atrial Contraction The ectopic P wave is often hidden in the ST-T wave of the preceeding beat

29 Premature Junctional Complex Captures the atria retrograde and the ventricles antegrade

30 Premature Ventricular Contractions Unifocal or multifocal Singles, couplets, triplets or salvos (4-6)

31 PVC: Compensatory Pause Top: Normal Rhythm Middle: PVC Blocks next sinus impulse Next impulse arrives on time Bottom: PAC No compensating pause

32 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

33 Ventricular Tachycardia

34 Ventricular Fibrillation No pumping action Fatal if not intervened by defibrillation

35 Ischemia Reduced blood supply Elevated membrane resting potential Shorter AP Steady injury current Elevated or depressed ST-segment

36 Concave and Convex ST segment

37 ST Segment Depression

38 ST Segment Sloping

39 Wolf-Parkinson-White Syndrome Abnormal pathway for impulse conduction between atrium and ventricle Atria to ventricles Ventricles to atria

40 Left Ventricular Hypertrophy Increased pump load Increased ventricular wall thickness Stronger electric sources

41 Right Ventricular Hypertrophy

42 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

43 Axis pointing to the left 1. avr is the weakest Perpendiculars: -60 or 120 deg. Negative leads II and III, so: -60 degree

44 Axis pointing to the right 1. avr is weakest Perpendiculars: -60 or 120 degrees Positive leads II and III, so 120 degrees

45 Electrocardiography 10 min Break

46 Monitoring Arrhythmia Two ECG leads Bandwidth: Hz Sampling frequency: 500 Hz Point-by-point sampling Online dual-lead display Online R-wave detection Online R-R interval charting Arrhrythmia alarms

47 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

48 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

49 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

50 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

51 Electrocardiography Labview demo