ECG Flashcards
Electrodes
material in contact with skin connected to cables
Cables/ Wires
Connected to electrodes
Leads
Perspective of electrical activity of the heart
Vector
quantity that has both magnitude and direction
Isoelectric line?
represents no net change in voltage. i.e. vectors are perpendicular to the lead.
Width of deflection=
duration of the event
Upward deflections are towards
the cathode (+)
Each wave is composed of both
both the up- and downstrokes
Downward deflections are towards
the anode (-)
Steepness of line denotes the
‘velocity’ of action potential
P wave=
The electrical signal that stimulates contraction of the atria (atrial systole)
QRS =
The electrical signal that stimulates contraction of the ventricles (ventricular systole)
No atrial repolarisation possible because QRS hides it
T wave=
The electrical signal that signifies relaxation of the ventricles
Conduction system parts
SA node Atrial myocardium AV node Bundle of His Endocardium Myocardium Epicardium
Why is lead II most important?
the negative electrode is on the right arm and positive electrode= right leg which is how the heart is lined up so deflections are most prominent here
Conduction system mapped to ECG
(know drawing of normal wave+ relate to each part)
(slide 11, lecture 13)
- SAN= P wave
Autorhythmic myocytes
Atrial depolarisation
Not big or fast= wide dome shaped
In diagram, red arrow pointing more towards positive which is why there is a positive wave - AVN
AVN depolarisation
Isoelectric ECG- flat line
Slow signal transduction
Protective - Bundle of His
Rapid conduction- purkinje cells- cells are organised lengthways
Insulated- small bit of the flat line continued - Bundle branches
Septal depolarisation
Small negative deflection
Small and fast, just to a small bit of muscle - Purkinje fibres (1)
Ventricular depolarisation
Massive depolarisation, lots of cells+ muscle, towards +ve
Impulse works its way up myocardium walls, up the sides on both but because its more prominent on LV= that side dominates
At this point its in full systole, has ejected blood - Purkinje fibres (2)
Late ventricular depolarisation - Fully depolarised ventricles
Isoelectric ECG- flat line - Repolarisation= T wave
Ventricular repolarisation, heading towards –ve electrode (-ve+ -ve= +ve) so positive deflection, not a rapid event so its wide
12 leads
View of heart+ coronary artery its referring to
1st columb: Lateral, LCx (Left circumflex) Inferior, RCA (Right coronary artery) Inferior, RCA 2nd column: n/a, n/a Lateral, LCx Inferior, RCA 3rd column: Septal, LAD (Left Anterior Descending Artery) Septal, LAD Anterior, RCA 4th column: Anterior, RCA Lateral, LCx Lateral, LCx
ECG one big square width+ depth meaning?
One width= 0.2s (each small square= 0.04s)
One depth= 0.5mV (each small square= 0.1mV)
Lead 1=?
Lead 2=?
Lead 3=?
Electrode placement?
Lead 1= RA to LA (-ve to +ve) (one L)
Lead 2= RA to LL (-ve to +ve) (two Ls)
Lead 3= LL to LA (+ve to -ve) (3 Ls)
First electrode of each pair= always -ve (first electrode= higher up/ to the left)
V1= Right sternal border, in the 4th intercostal space V2= Left sternal border in the 4th intercostal space V3= Halfway between V2 and V4 (put after V4) V4= Mid-clavicular line In the 5th intercostal space V5= Anterior axillary line at the level of V4 V6= Mid-axillary line at the level of V4
12 leads table
(slide 14, lecture 13)
Location, Polarity, Plane, Cathode (+ve), Anode (-ve), View
Polarity= how many physical points are there in the line (most of them aren’t from one electrode to another)
PR interval
Measure from P to Q actually (sometimes you can’t see it)
How to find heart rate on ECG
60/ RR interval
Divide 300 by number of big squares
How to find QRS axis
Can’t be worked out just from one lead
If you get another lead that has another 90 degree view from the first lead you can calculate it (e.g. Lead II and aVL)
1. Find net deflection of highest and lowest part of ECG (count from highest point to 0 then 0 to lowest point and subtract down from up)
2. Therefore in Lead II direction, draw arrow of net value
3. Do the same as 1 for second lead (aVL in this case) and from the end of the arrow of the first lead, draw the arrow of the value parallell to direction of second lead (90 degrees)
4. This means that the cardiac axis (one cardiac vector) is the sum of those two arrows
5. Find the angle in the triangle by trigonometry
6. Figure out angle from the line that combines the lines you’ve drawn to the 0 line (in this case its 60- angle)
Types of arrhythmias
Supraventircular = problems that originate above AV node Junctional= junction between atria+ ventricles= AV node/ could be in bundle branches Ventricular= ventricular muscle itself
Types of abnomalities of the heart
Conduction abnormalities
Structural abnormalities, e.g. LV hypetrophy= muscle grows concentrically into ventricle= axis deviation
Perfusion abnormalities, e.g. narrowing/ blockage of arteries= ischamic tissue
Parts of heart
slide 5, lecture 14
-
Things to look for in an ECG
1) Rate+ Rhythm (RR)
2) P wave+ PR interval- shows how long the signal takes to go through Atrial myocardium + AV node (supposed to be slower)
3) QRS duration
4) QRS axis (trigonometry)
5) ST segment- focus on height
Sinus rhythm
Rate=?
Each P-wave is followed by a QRS wave (1:1)
Rate is regular (even R-R intervals) and normal (83 bpm)
Types of ECG abnormalities
Know general shapes from lecture
Supraventricular abnormalities: Sinus bradycardia Sinus tachycardia Sinus arrhythmia Atrial fibrillation Atrial flutter
Junctional arrhythmias: First degree heart block Second degree heart block (Mobitz I) Second degree heart block (Mobitz II) Third degree heart block
Ventricular arrhythmias: Ventricular tachycardia Ventricular fibrillation ST elevation ST depression
Sinus bradycardia
Rate?
Causes?
Each P-wave is followed by a QRS wave (1:1)
Rate is regular (even but long R-R intervals) and slow (56 bpm)
Can be healthy, caused by medication or vagal stimulation
Sinus tachycardia
Rate?
Cause?
Each P-wave is followed by a QRS wave (1:1)
Rate is regular (even but short R-R intervals) and fast (107 bpm)
Often a physiological response (i.e. secondary)
How to tell if heart is left-axis deviated or right axis deviated?
Look at QRS complex on Leads I and III
If Lead I is positive, Lead III is negative (both moving in opposite directions)= LEFT axis deviated
If Lead I is negative, Lead III is positive (both moving towards each other= RIGHT axis deviated
Sinus arrhythmia
Rate?
Each P-wave is followed by a QRS wave
Rate is irregular (variable R-R intervals) and normal-ish (65-100 bpm)
R-R interval varies with breathing cycle
Atrial fibrillation Baseline? Rhythm? Rate? Increase what risk? Why can you still live with it?
Oscillating baseline – atria contracting asynchronously
Rhythm can be irregular and rate may be slow
Turbulent flow pattern increases clot risk
Atria not essential for cardiac cycle
Atrial flutter
Baseline?
Atria: Ventricular beats?
Regular saw-tooth pattern in baseline (II, III, aVF)
Atrial to ventricular beats at a 2:1 ratio, 3:1 ratio or higher
Saw-tooth not always visible in all leads
First degree heart block- can usually see in rhythm strip
Interval caused by?
Rhythm?
Sign of?
Prolonged PR segment/interval caused by slower AV conduction
Regular rhythm: 1:1 ratio of P-waves to QRS complexes
Most benign heart block, but a progressive disease of ageing
Second degree heart block (Mobitz I) -can usually see in rhythm strip
Regularity?
Cause?
Also called?
Gradual prolongation of the PR interval until beat skipped
Most P-waves followed by QRS; but some P-waves are not
Regularly irregular: caused by a diseased AV node (4th signal not conducted through AV node)
Also called Wenckebach
Second degree heart block (Mobitz II)
Regularity?
Danger?
P-waves are regular, but only some are followed by QRS
No P-R prolongation but doesn’t come through sometimes
Regularly irregular: successes to failures (e.g. 2:1)
Can rapidly deteriorate into third degree heart block
Third degree heart block
P-waves are regular, QRS are regular, but no relationship (atria and ventricles have no relationship)
P waves can be hidden within bigger vectors (e.g. P waves ‘move left’ because less frequent that QRS)
A truly non-sinus rhythm SA, AV and myocardium all have their own autonomic rates (decrease as you go through) but because SA is quickest it usually controls the rest but this doesn’t happen here– back-up pacemaker in action
Ventricular tachycardia
Rate?
High risk of?
P-waves hidden – dissociated atrial rhythm
Rate is regular and fast (100-200 bpm)
Ventricular vectors= regular
At high risk of deteriorating into fibrillation (cardiac arrest) but shockable rhythm – defibrillators widely available
Ventricles= beating faster than they can fill
Ventricular fibrillation
Heart rate?
High risk of?
Heart rate irregular and 250 bpm and above
Heart unable to generate an output- brain doesn’t get blood
Not every wave looks the same
At high risk of deteriorating into fibrillation (cardiac arrest) Shockable rhythm – defibrillators widely available
ST elevation
Rhythm?
Rate?
Caused by?
P waves visible and always followed by QRS
Rhythm is regular and rate is normal (85 bpm)
ST-segment is elevated >2mm above the isoelectric line
Caused by infarction (tissue death caused by hypoperfusion)
Therefore >2mm elevation= infarction
ST depression
Rhythm?
Rate?
Caused by?
P waves visible and always followed by QRS
Rhythm is regular and rate is normal (95 bpm)
ST-segment is depressed >2mm below the isoelectric line
Caused by myocardial ischaemia (coronary insufficiency)- Coronary arteries cant provide myocardium with enough oxygen
