ECG Basics Flashcards
Normal values
P wave
Less then 120ms, or 3 small squares.
First positive deflection on the ECG.
Represents atrial depolarisation.
QRS width
Normal width 70-100ms
Narrow complex = less than 100ms. Supraventricular (above the ventricles) in origin.
Wide complex = more than 100ms. Ventricular in origin, or due to abnormal conduction.
Represents ventricular depolarisation.
T wave
Represents ventricular repolarisation.
Positive deflection after each QRS complex
Should be upright in all leads except aVR and V1.
PR Interval
From the start of the P wave to the start of the QRS.
Normal length is between 120 - 200ms (3-5 small squares).
Longer than 200ms = first degree heart block.
Shorter than 120ms = suggests pre-excitation (conduction through an accessory pathway between the atria and the ventricles e.g. Wolff-Parkinson White).
PR segment
Flat, isoelectric segment between the end of the P wave and the start of the QRS
For patients with MI, depression or elevation in this segment indicates corresponding atrial ischemia or infarction.
Widespread depression can be indicative of pericarditis.
QT Interval
From the start of the Q wave to the end of the T wave.
Should be measured in lead II or V5/6.
Inversely proportional to heart rate.
Faster heart rate = shorter QT interval.
Slower heart rate = longer QT interval
Prolonged QT is associated with increased risk of ventricular arrhythmias, especially Torsades de Pointes.
Congenital short QT syndrome is associated with increased risk of paroxysmal atrial and ventricular fibrillation, and sudden death.
Corrected QT Interval (QTc)
Prolonged QTc for men: more than 440ms.
Prolonged QTc for women: more than 460ms.
Abnormally short QTc if less than 350ms.
Calculated from the existing rhythm strip to give the QT interval for a heart rate of 60bpm, making it easier to tell if prolonged or shortened.
J point
Junction between the end of the QRS complex and the beginning of the ST segment.
ST Segment
Flat, isoelectric segment between the end of the S wave (the J point) and the beginning of the T wave.
Represents the interval between ventricular depolarisation and repolarisation.
Can be elevated or depressed due to a number of causes.
Causes of ST segment elevation
Acute myocardial infarction Coronary vasospam (Printzmetal's angina) Pericarditis Benign early repolarisation Left bundle branch block Right bundle branch block Ventricular aneurysm Brugada syndrome Ventricular paced rhythm Raised Intracranial pressure Takotsubo cardiomyopathy
Septal ECG leads
V1 & V2
Septal wall of the left ventricle.
Often grouped together with Anterior leads.
Reciprocal leads are posterior.
Anterior ECG leads
V3 & V4
Anterior wall of the left ventricle.
Often grouped together with Septal leads.
Reciprocal leads are Posterior.
Area usually supplied by the Left anterior descending artery.
Lateral ECG leads
1, aVL, V5 & V6.
Shows the lateral wall of the left ventricle.
Reciprocal to Inferior leads.
Usually supplied by branches of the Left anterior descending artery (LAD) and the Left circumflex artery (LCx).
Inferior ECG leads
II, III & aVF.
Shows the inferior wall of the left ventricle.
Reciprocal to Lateral leads.
Normally supplied by the Right coronary artery (RCA). Some patients (18%) have a dominant Left circumflex artery (LCx) which supplies this area.
Posterior ECG leads
V7, V8 & V9.
Reciprocal to septal and anterior leads.
Usually supplied by the Posterior descending artery.
