ECG Interpretation for Primary Care Physician Aamir A. Cheema M.D.
P akistan S ociety of F amily P hysicians
Rate 300-150-100-75-60-50 300-150-100-75-60-50
What if rate is <50/min or rhythm is irregular ? Count the number of R waves in a 6 second strip and multiply by 10. For example, if there are 7 R waves in a 6 second strip, the heart rate is 70 (7x10=70).
1. Locate the P wave
If absent and rhythm is irregular, think of atrial fibrillation.
If present- check rate: If <60, bradycardia. If >100, tachycardia.
In general, if narrow-complex tachycardia is present and heart rate is
100-150, think of sinus tachycardia
150-250, think of SVT (supraventricular tachycardia)
250-350, think of atrial flutter
>350, think of atrial fibrillation
2. Establish the relationship between P wave and QRS complex
If 1:1, it is normal
If more P waves than QRS complexes, think of AV block
If more QRS complexes than P waves, think of accelerated junctional or ventricular rhythm
3. Analyze the QRS morphology
If normal duration (<120 msec), think of supraventricular origin e.g. normal sinus rhythm or supraventricular tachycardia
If wide (>120 msec), think of ventricular origin e.g. ventricular tachycardia
Intervals PR interval: <200 msec (one big box) QRS complex:<100 msec (2½ small boxes) ST segment: evaluate for elevation or depression below baseline QT segment: roughly less than half of R-R interval At high or low heart rates, calculate corrected QT interval QTc = QT interval ÷ square root of the RR interval (in sec) The normal value for the QTc is <440 msec (2½ big boxes)
Left ventricular hypertrophy criteria
Sum of S wave in V1 and R wave in V5 or V6 3.5 mV (35 mm)
R wave in aVL 1.1 mV (11 mm)
Clinically significant ST segment elevation is considered to be present if it is greater than 1 mm (0.1 mV) in at least two contiguous precordial leads or in at least two adjacent limb leads.
One or more of the precordial leads (V1-V6) and leads I and aVL suggest anterior wall ischemia or infarction Leads V4 to V6 suggest apical or lateral ischemia or infarction
Leads V1 to V3 suggest anteroseptal ischemia or infarction.
Leads II, III, and aVF suggest inferior wall ischemia or infarction
ST elevation in II, III and aVF (inferior wall MI)
T wave inversion in V4-6 (lateral wall MI)
Posterior wall MI
The ST elevations of acute posterior MI are usually associated with reciprocal ST depressions in leads V1 to V3.
Posterior inferior wall MI can be differentiated from anterior wall ischemia by the presence of ST segment elevations in the inferior (II, III, aVF). Relatively tall R waves may also appear in leads V1-V3, corresponding to the appearance of pathologic Q waves (loss of depolarization forces) in the posterior leads.
ST depression is defined by an ST segment which is depressed >1 mm below the baseline
Typically there are ST segment changes associated with T wave flattening or inversion; isolated T wave changes are not usually seen with ischemia.
New LBBB: Treat as ST Elevation MI i.e. rush to cath lab for PCI LBBB Diagnosis: Slurring of S wave in V5 and V6 and QRS duration > 100 msec (i.e more than 2½ small squares)
Abnormal Q wave
According to the new criteria, an abnormal Q wave is any Q wave in leads V1 to V3 or a Q wave 30 msec in leads I, II, aVL, aVF, or V4 to V6; the Q wave must be present in any two contiguous leads and 1 mm in depth.
(European Society of Cardiology (ESC) and American College of Cardiology (ACC) 2000)
Absent P waves
Irregulary irregular rhythm
Sinus rhythm with complete (third-degree) heart block. There is independent atrial (as shown by the P waves) and ventricular activity, with respective rates of 83 and 43 beats/min.
Mobitz type I (Wenckebach) second degree AV block
A progressively increasing PR interval until a P wave is not conducted (arrow)