<<

Electrocardiography

31650 Kaj-Åge Henneberg

Plan Function of cardiovascular system Electrical activation of the Recording the ECG detection methods Group Work The Heart as a Pump Internal View of Heart Arterial Circulation Venous Circulation Heart Valves

Mitral valve: Left AV valve : Right AV 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 and 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 types Refractory period Wave propagation

Show isochrone overhead Elementary dipole source Mean dipole source = Heart Vector Autonomic Innervation

Parasympathetic: Acetylcholine Right vagus to SA node Left 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 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 ECG Segments and Intervals Normal ECG Leads Electrocardiography

10 min Break Arrhythmia

Abnormal ECG waveforms Atrial origin AV origin Ventricular origin Atrial Premature Atrial Contraction

The ectopic P wave is often hidden in the ST- 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 or fibrillation

No pumping action Fatal if not intervened by

Reduced supply Elevated membrane resting potential Shorter AP Steady current Elevated or depressed ST-segment Concave and Convex ST segment ST Segment Depression ST Segment Sloping -Parkinson-White Syndrome

Abnormal pathway for impulse conduction between and Atria to ventricles Ventricles to atria Left

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 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 : RR > 1000 ms : 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