Cardiology Flashcards
How to calculate heart rate on ECG?
Regular
Count the number of large squares present within one R-R interval.
Divide 300 by this number to calculate heart rate.
Irregular
Count the number of complexes on the rhythm strip (each rhythm strip is typically 10 seconds long).
Multiply the number of complexes by 6 (giving you the average number of complexes in 1 minute).
How to interpret ECG
Rate
Rhythm
Cardiac axis
P waves
PR interval
QRS complex
ST segment
Right axis deviation?
Lead III has the most positive deflection, and lead I should be negative.
Right axis deviation is associated with right ventricular hypertrophy.
Left axis deviation?
Lead I has the most positive deflection.
Leads II and III are negative.
Left axis deviation is associated with heart conduction abnormalities.
What is a normal PR interval?
120-200ms (3-5 small squares)
what is considered first degree heart block?
> 0.2 seconds
what is second degree heart block type 1?
Second-degree AV block (type 1) is also known as Mobitz type 1 AV block or Wenckebach phenomenon.
Typical ECG findings in Mobitz type 1 AV block include progressive prolongation of the PR interval until eventually the atrial impulse is not conducted and the QRS complex is dropped.
AV nodal conduction resumes with the next beat, and the sequence of progressive PR interval prolongation and the eventual dropping of a QRS complex repeats itself.
What is second degree heart block type 2?
Second-degree AV block (type 2) is also known as Mobitz type 2 AV block.
Typical ECG findings in Mobitz type 2 AV block include a consistent PR interval duration with intermittently dropped QRS complexes due to a failure of conduction.
The intermittent dropping of the QRS complexes typically follows a repeating cycle of every 3rd (3:1 block) or 4th (4:1 block) P wav
What is 3rd degree heart block?
Third-degree (complete) AV block occurs when there is no electrical communication between the atria and ventricles due to a complete failure of conduction.
Typical ECG findings include the presence of P waves and QRS complexes that have no association with each other, due to the atria and ventricles functioning independently.
Cardiac function is maintained by a junctional or ventricular pacemaker.
Narrow-complex escape rhythms (QRS complexes of <0.12 seconds duration) originate above the bifurcation of the bundle of His.
Broad-complex escape rhythms (QRS complexes >0.12 seconds duration) originate from below the bifurcation of the bundle of His.
what can cause a shortened PR interval?
Simply, the P wave originates from somewhere closer to the AV node, so the conduction takes less time (the SA node is not in a fixed place, and some people’s atria are smaller than others).
The atrial impulse is getting to the ventricle by a faster shortcut instead of conducting slowly across the atrial wall. This accessory pathway can be associated with a delta wave (see below)
what is considered a narrow and broad QRS?
Narrow < 0.12 seconds
Broad > 0.12 seconds
LBBB and RBBB
Left - W in V1 and M in V6
Right M in V1 and W in V6
what can lead to tall QRS complexes?
Tall complexes imply ventricular hypertrophy (although can be due to body habitus e.g. tall slim people). There are numerous algorithms for measuring LVH, such as the Sokolow-Lyon index or the Cornell index.
what is a delta wave?
delta wave‘ indicates that the ventricles are being activated earlier than normal from a point distant from the AV node. The early activation then spreads slowly across the myocardium, causing the QRS complex’s slurred upstroke.
The presence of a delta wave does NOT diagnose Wolff-Parkinson-White syndrome. This requires evidence of tachyarrhythmias AND a delta wave.
What is a Q wave?
Isolated Q waves can be normal.
A pathological Q wave is > 25% the size of the R wave that follows it or > 2mm in height and > 40ms in width.
A single Q wave is not a cause for concern – look for Q waves in an entire territory (e.g. anterior/inferior) for evidence of previous myocardial infarction.
what may poor r wave progression indicate?
can be sign of previous MI
What is the J point segment?
The J point is where the S wave joins the ST segment.
This point can be elevated, resulting in the ST segment that follows it being raised (this is known as “high take-off”).
High take-off (or benign early repolarisation) is a normal variant that causes a lot of angst and confusion as it LOOKS like ST elevation.
what is considered ST elevation?
ST-elevation is significant when it is greater than 1 mm (1 small square) in 2 or more contiguous limb leads or >2mm in 2 or more chest leads.
What is considered ST depression?
ST depression ≥ 0.5 mm in ≥ 2 contiguous leads indicates myocardial ischaemia.
What do t waves represent?
repolarisation of the ventricles
what is considered tall t waves and what can they be associated with?
> 5mm in the limb leads AND
10mm in the chest leads (the same criteria as ‘small’ QRS complexes)
Tall T waves can be associated with:
Hyperkalaemia (“tall tented T waves”)
Hyperacute STEMI
in which leads are t waves usually inverted?
V1
lead III
what may lead to pathological t waves?
Ischaemia
Bundle branch blocks (V4-6 in LBBB and V1-V3 in RBBB)
Pulmonary embolism
Left ventricular hypertrophy (in the lateral leads)
Hypertrophic cardiomyopathy (widespread)
General illness
what can cause biphasic t waves?
biphasic t waves have two peaks - can indicate ischaemia and hypokalaemia