ECG Flashcards Preview

Semester 2 > ECG > Flashcards

Flashcards in ECG Deck (25):

Limb leads


Directions of waves of the ECG

Depolarisation towards electrode - Positive
Repolarisation towards electrode - Negative

Depolarisation away from electrode - Negative Repolarisation away from electrode - Positive

If depolarisation is perpendicular, produces a biphasic curve

N.B. depolarisation spreads out across the wall of the ventricle, repolarisation spreads inwards


What determines wave amplitude of the signal on an ECG

Mass of myocardium being measured (larger muscles produce large signals)

Rate of depolarisation or repolarisation (depolarisation produces larger signals)


Which limb leads look at the inferior surface of the heart?

Lead II,  aVF,  (lead II)


Which limb leads look at the right side of the heart?

aVR, lead III 


Which limb leads look at the left side of the heart?

aVL, lead I, lead II


Leads that look at the right atrium

V1, V2, aVR


What characteristic should you see in the ECG from V1-V6

Progression of the R wave from prominently downward (V1) to prominently upwards (V6)


PR interval

Conduction from the atria to the ventricles (from SA node>AV node>bundle of His)



QRS interval

< 120ms

Ventricular depolarisation


QT interval

ventricular depolarisation and repolarisation

varies with heart rate


How to report an ECG


Conduction intervals

Cardiac axis

Description of QRS

Description of ST segments and T waves


First degree heart block

Prolonged PR interval

Delay in the pathway from SA node to ventricles


Second degree heart block

Failure of excitation to pass through the AV node or bundle of His

Mobitz type 2: constant PR interval with dropped QRS complex

Wenckebach: progressive lengthening of PR interval with dropped QRS

2:1 type : two pay waves per QRS, normal constant PR interval


Third degree heart block

Occurs when atrial contraction is normal but no beats are conducted to the ventricles. 

No relationship between P waves and QRS complex


 Right bundle branch block

No conduction down the right bundle branch but septum depolarised from left to right as normal. 

RSR' pattern in V1, QRS complex with deep S wave in V6

Nrmal cardiac axis


Left bundle branch block

Conduction down the left bundle branch ffails. Septum becomes depolarised from right to left. 

Broad M pattern QRS complex in V4-V6

Left axis deviation


Could be due to aortic stenosis or ischaemic disease


Which leads are used to derive the cardiac axis?

Leads I, II and III QRS complex.

Upward deflections seen in all three leads, most prominent in lead II in a normal axis.

RV hypertrophy causes right axis deviation, prominent upward deflection in lead III

LV hypertrophy causes left axis deviation. Results in negative deflection in lead II and lead III



What happens to the cardiac action potential in ischemia?

Shortened in ischemia because the compromised metabolic state opens K+ channels which cause hyperpolarisation. 

Causes current flow between ischemic and normal myocardium during systole, giving rise to a signal during QRS and T


ECG changes in exercise induced ischemia

ST depression 

Ischaemic region returns to rest during the ST interval but the non-ischaemic region is still active. 


ST elevation

Characteristic of acute MI.

Severe transmural myocardial ischemia. Ischemic region returns to rest in ST interval but unaaffected part of the heart is still depolarised. 

Current flows away from electrode in lead II. 


Regions of the heart in ECG

Anterior heart supplied by LAD artery

Anterolateral - diagonal branch of LAD

Lateral heart supplied by Left circumflex

Inferior heart supplied by right coronary


Acute posterior MI

ST depression in V1-V3 (look at anterior heart)

Tall R wave in V1 and V2


ECG changes seen with progression of STEMI

Before - normal ECG

Severe ischemia - ST elevation, Peak in T wakes, followed by T wave inversion

Infarction - Loss of R-wave progression, less ST elevation, development of pathological (wide) Q waves

Fibrosis - normal ST segment and T wave, wide W waves persist. 


ECG changes seen with NSTEMI

Before - normal ECG

Ischemia - ST depression and T wave inversion

Infarction - ST depression and T wave inversion

Fibrosis - ST returns to baseline, T wave inversion persists. 

Decks in Semester 2 Class (70):