PQRST ECG questions Flashcards
Describe the quadrant method for determining axis deviation
Look at lead I and aVF
Examine QRS to determine if positive, isoelectric or negative
A positive QRS in lead I puts the axis in roughly the same direction as lead I
A positive in aVF aligns the axis with aVF
Combine both areas - the quadrants that overlap determine the axis
Add in lead II for greater accuracy
Describe the isoelectric method for axis determination
If the QRS is positive in any given lead the axis points in roughly the same direction
If the QRS is negative the the axis is roughly in the opposite direction
If the QRS is isoelectric then the axis is at 90 to this lead
What is the usual ECG paper speed?
25mm/s
How many seconds per small and big squares?
1mm = 0.04 secs (small square) 5mm = 0.2 secs (big square)
How do you estimate rate on an ECG - 3 methods
- 300/number of large squares R-R
- 1500/small squares R-R (useful for very fast heart rates)
- Number of complexes on rhythm strip x 6 (= average rate over 10 sec period)(useful in slow or irreg ECGs)
What is a u wave?
Small (0.5mm) deflection immediately following the T wave
- usually in the same direction as the T wave
- best seen in V2+V3
- Gets bigger with slower heart rates
Prominent or inverted U waves are abnormal
What causes prominent U waves?
Hypocalcaemia Hypomagnesaemia Hypothermia Raised ICP LVH Hypertrophic cardiomyopathy Digoxin Phenothiazines Class Ia and II antiarrythmogenics
What causes inverted U waves?
CAD HTN Valvular heart disease Cardiomyopathy Hyperthyroidism Congenital heart disease
Describe the PR interval
Time from onset of P wave to start of QRS
Reflects conduction through the AV node
Normally 120-200ms (3-5 small squares)
Describe the abnormalities of the PR interval
1st degree heart block - Prolonged PR
2nd degree heart block
- Mobitz type 1: successive prolongation until a QRS in dropped (Wenkebach)
- Mobitz type 2: intermittent non-conducted p wave (no successive prolongation)
Short PR interval occurs in pre-excitation syndromes and AV nodal (junctional) rhythms
What is the PR segment?
The flat, usually isoelectric segment between the end of the p wave and the start of the QRS
Describe the abnormalities that can occur with the PR segment
Pericarditis: PR segment depression, wide-spread ‘saddle-shaped’ ST elevation, reciprocal ST depression and PR elevation in aVR and V1
Atrial ischaemia: PR segment elevation or depression in patients with MI indicates concomitant atrial ischaemia or infarction
What is the QT interval?
The time from the start of the Q until the end of the T wave
Represents time for ventricular depolarisation and repolarisation
Inversely proportional to hr
How do you calculate QTc?
QT divided by thr square root of RR (in seconds = 60/hr)
When is QTc prolonged?
> 440ms men
460ms women
500ms is associated with an increased risk of torsades
What causes prolonged QTC?
Hypokalaemia Hypomagnesaemia Hypocalcaemia Hypothermia Myocardial ischaemia Post-cardiac arrest Raised ICP Congenital Drugs
What causes QTC < 350ms?
Hypercalcaemia
Congenital
Digoxin
What is the ST segment?
The flat, isoelectric section between the end of the s wave (j point) and the beginning of the T wave
Represents the interval between ventricular depolarisation and repolarisation
What causes ST elevation?
AMI Printzmetals angina Pericarditis Benign early repolarisation LBBB LVH Ventricular aneurysm Brugada syndrome Ventricular paced rhythm Raised ICP
Which leads are septal?
V1-2
Which leads are anterior?
V3-4
Which leads are lateral?
I, aVL, V5-6
Which leads are inferior?
II, III, aVF
Which leads are RV
V1, V4R
Which leads are posterior?
V7-9
What causes ST depression
Ischaemia NSTEMI Post MI Digoxin (reverse tick) Hypokalaemia SVT RBBB LBBB LVH Paced rhythm
What is the width of a normal QRS complex?
Normally 70-100ms
< 100ms are supraventriclaur in origin - SA, atria, AVN
>100 are either ventricualr or due to abberant conduction
What causes broad QRS complexes?
BBB (>120ms needed for diagnosis) Hyperkalaemia TCA OD WPW Paced rhythm Hypothermia
What causes QRS of altering height?
Normally due to a massive pericardial effusion
What does a T wave represent?
Ventricaular repolarisation
What are the characteristics of a normal T wave?
Upright except aVR and V1
Amplitutde < 5m in limb leads and < 15mm precordial leads
What causes T wave abnormalities
Hyperkalaemia - peaked
Hyperacute - STEMI
Inverted - MI, ischaemia, normal in kids, BBB, ventricular hypertrophy, PE, hypertrophic cardiomyopathy, raised ICP
Biphasic - myocardial ischaemia (T waves go up the down), hypokalaemia (T waves go down then up), Wellen’s syndrome
Where on the ECG axis are each of the leads?
O - I \+60 - II \+90 - aVF \+120 - III -150 - aVR -30 aVL
What is an r wave?
The first upward deflection after the P wave
It represents early ventricular depolarisation
What are the 3 key abnormalities that occur with the r wave?
- Dominant R in V1 - RVH, RBBB, post MI, WPW type A, incorrect lead placement, dextrocardia, hypertrophic cardiomyopathy, normal in kids and young adults
- Dominant R in aVR - sodium channel blocking drug toxicity, dextrocardia, incorrect lead placement, VT
- Poor R wave progression - R wvae < 3mm in V3 due to anteroseptal MI, LVH, inaccurate lead placement, may be normal
What is a Q wave?
Any negative deflection that precedes and R wave
Represents normal L-R depolarisation of the IV septum
Small septal Q waves typically seen in left sided leads
When is a Q wave pathological?
>40ms (1mm wide) > 2mm deep > 25% of depth of the QRS complex Seen in leads V1-3 May indicate current or prior MI
Describe a normal p wave?
normally smooth, monophasic, should be upright in I, II and inverted in aVR
< 120ms
amplitutde: <2,5mm in limb leads, < 1,5 in precordial leads
What happens to p waves in right atrial enlargement?
lead II - p waves taller
What happens to p waves in left atrial enlargement>?
lead II - duration > 120ms
What are the common abnormalities of p waves?
p mitrale - LAE classically due to mitral stenosis
p pulmonale - RAE usually due to pulmonary hypertension
Inverted - non-sinus in origin
Variable morphology - multifocal atrial rhythm
