ELECTROCARDIOGRAPHY AND RHYTHM DISORDERS Flashcards
What is a lead?
Measurement of electrical activity of the heart from a certain perspective/angle
How many electrodes, cables/wires and leads?
10 electrodes
10 cables/wires
12 leads
What does an isoelectric line represent in an ECG?
No net change in voltage - vectors are perpendicular to the lead
What does the width of the deflection denote?
The duration of the event
What does the steepness of the line in an ECG denote?
Velocity of action potential
Upward and downward deflections indicate…
Upwards indicate they are towards +ve electrode and vice versa
What does the P wave indicate?
The electrical signal which stimulates atrial systole (contraction)
What does the QRS complex indicate?
The electrical signal that stimulates ventricular systole (contraction)
What does the T wave represent?
The electrical signal that signifies ventricular relaxation
What is the rule of Ls?
Lead I = right arm to Left arm
Lead II = right arm to Left Leg
Lead III = Left arm to Left Leg
What is the rule of reading?
If the 3 leads drawn out into triangle, left to right and top to bottom the first electrode encountered of each bipolar pair in a lead is always negative
Name the 3 augmented vector leads and their paths
aVR - Right arm (+ve) to midpoint of of lead III (-ve)
aVL - Midpoint of lead II (-ve) to left arm (+ve)
aVF - Left leg (+ve) to midpoint of lead I (-ve)
Where are the chest electrodes of an ECG placed
V1 - Right sternal border, 4th intercostal space
V2 - Left sternal border, 4th intercostal space
V3 - Halfway between V2 and V4
V4 - Mid-clavicular line, 5th intercostal space
V5 - Anterior axillary line, same level as V4
V6 - Mid-axillary line at level of V4
What does each little square on an ECG represent?
0.04 secs
What does atrial fibrillation look like on an ECG?
Oscillating baseline with atria contracting asynchronously
What does atrial flutter look like on an ECG?
Regular saw-tooth pattern in baseline
Atrial to ventricular beats at a 2:1, 3:1 ratio or higher
What does a first degree heart block look like on an ECG?
Prolonged PR interval due to slower AV conduction
What does a second degree heart block (Mobitz I) look like on an ECG and what is it caused by?
Gradual prolongation of PR interval until beat skipped
Most P-waves followed by QRS but some P-waves not
Due to diseased AVN - regularly irregular
What does a second degree heart block (Mobitz II) look like on an ECG?
Not all P-waves followed by a QRS complex
No P-R elongation
Regularly irregular
Can rapidly deteriorate into 3rd degree heart block
What does a third degree heart block look like on an ECG?
No relationship between P-waves and QRS complex. Both still regular but occur anywhere in heart beat
P-waves can be hidden in bigger vectors
Non-sinus rhythm (SAN has no influence) - back up pacemaker in action
What does ventricular tachycardia look like on an ECG?
P-waves hidden causing dissociated atrial rhythm due to ventricle beating so fast. Regular rate is 100-200 bpm.
P40 notes
What are patients with ventricular tachycardia at high risk of?
Deteriorating into fibrillation (cardiac arrest)
Which heart rhythm irregularities are shockable with defibrillators?
Ventricular tachycardia
Ventricular fibrillation
What does ventricular fibrillation look like on an ECG?
Irregular heart rate and 250+ bpm (more frequent than ventricular tachycardia)
