Clinical Interpretation Of The ECG

4.9.06

Atrial depolarisation + contraction = P wave.
AVN depolarisation = PR interval.
Ventricular depolarisation = QRS complex.
Ventricular repolarisation = T wave.

Iso-electric line represents resting potential of heart.
Positive deflections show electricity flowing towards lead and vice versa.

Assessing ECG
• Rate.
• Rhythm.
• Axis.
• P wave.
• P-R interval.
• QRS complex.
• S-T segment.
• T wave.

• Patient's details.
• Date and time.
• Condition of patient.

• 10 second rhythm strip - usually lead II:
-rate;
-rhythm:
§P wave;
§P-R interval.

Calculating ventricular rate
Eg. 1500 small squares = 1 minute.
R-R interval = 21 small squares.
1500/21 = 71 bpm.

Eg. irregular rate.
25 large squares = 5 seconds.
8 complexes in 25 large squares x 12 = 96 bpm.

Rate
• Tachycardia >100bpm.
• Bradycardia <50bpm. block =" P-R" i =" P-R" block =" No" fibrillation =" No">25% height of accompanying P wave;
-if wider than 1 small square;
-not seen if ischaemia damage does not involve entire thickness of ventricular wall.

Narrow complex tachycardia: impulse passes through AVN.
Broad complex tachycardia: impulse does not involve AVN.

Right bundle branch block
• Right ventricle activated belatedly by wave from left ventricle.
• Can be associated with right-sided cardiac problems:
-chronic lung disease;
-cardiomyopathy;
-atrial and ventricular septal defects.

Left bundle branch block
• Activity in left ventricle delayed.
• Usually indicates underlying cardiac pathology:
-coronary artery disease;
-acute MI etc.

ST segment
• Normal <3>