ECG Flashcards
A patient is noted to have an abnormally shortened PR-interval on their ECG. What is the most likely cause?
Wolf Parkinson White Syndrome
A short PR-interval indicates short conduction time between the atria and ventricles. This is due to an accessory pathway known as “the bundle of kent” is present between the atria and ventricles in WPW. Most individuals are asymptomatic but there is a risk of sudden death without treatment.
The absence of P-waves and an irregular rhythm would suggest a diagnosis of…
Atria fibrillation
In atrial fibrillation the atria no longer conduct electricity from the SA in an orderly fashion. Therefore P-waves are lost. As a result, only occasional waves of depolarisation pass through to the AV node and cause ventricular activation. This causes the irregular rhythm.
What is the normal duration of a QRS complex?
0.12 seconds ( 3 small squares)
If a QRS complex lasts longer it is described as a “wide QRS” and may be due to inefficient conduction of the ventricles such as bundle branch block.
What view of the heart do leads II, III and aVF represent?
Inferior
What is a common cause of right axis deviation?
Right ventricular hypertrophy
The increased muscle mass of the right ventricle causes increased signal on the ECG. As a result the axis of the heart is shifted to the right with lead III becoming more positive and lead I and II becoming less positive.
What view of the heart do leads I, aVL, V5 and V6 represent?
Lateral view
What view of the heart do leads V3 & V4 represent?
Anterior
What would it suggest if lead I became more positive than lead II and lead III became negative?
Left axis deviation
What view of the heart do leads V1 & V2 represent?
Septal
The duration of the PR interval is noted to be increasingly prolonged. In addition QRS complexes appear to be dropped at regular intervals. What diagnosis would this suggest.
Second degree - Mobitz Type 1 - Heart Block
Heart block in the disease of the AV node.
What is the most common cause of left axis deviation?
Defect of the conduction system
LAD is rarely due to left ventricular hypertrophy and more often due to defects in the conduction system.
If ST-elevation was noted in leads II, III and aVF what would it suggest?
An inferior MI
Leads II, III and aVF all look at the heart in the inferior plane.
Which artery is most likely to be affected if ST elevation in present in leads V3 and V4?
Left anterior descending coronary artery
ST elevation in leads V3 and V4 suggests an anterior infarct. The anterior portion of the heart is supplied mainly by the left anterior descending artery
What is often the earliest ECG change seen during myocardial infarction?
Tall peaked T waves
Tall peaked T-waves can suggest a number of abnormalities. If seen in all leads then they usually suggest the individual has hyperkalaemia. However if tall T waves are seen in a particular group of leads it suggests early MI. The tall T waves are due to potassium leaking through the damaged membrane over the infarcted area.
What would it suggest if lead I became negative and lead III became more positive than lead
Right axis deviation
