What is the proper procedure for reading and interpreting an electrocardiogram (EKG)?

Systematic Approach to EKG Interpretation

Use a structured, stepwise method to interpret every EKG, systematically evaluating rate, rhythm, axis, intervals, and waveform morphology to avoid missing critical diagnoses. 1

Step 1: Calculate Heart Rate

• Count the number of QRS complexes in a 6-second strip and multiply by 10, or use the formula 300 divided by the number of large boxes between consecutive R waves 1, 2
• Normal sinus rhythm ranges from 60-100 beats per minute in adults 2
• Sinus bradycardia (<60 bpm) may be normal in athletes, while sinus tachycardia (>100 bpm) can occur during physiological stress 2

Step 2: Assess Rhythm and Regularity

• Identify the underlying rhythm by examining P wave morphology and its relationship to QRS complexes 1
• Sinus rhythm is characterized by a P wave before each QRS complex with consistent PR interval 2
• Evaluate R-R intervals for consistency to determine rhythm regularity 1
• Note any irregularities such as premature beats, pauses, or completely irregular patterns that might suggest atrial fibrillation 2

Step 3: Measure Critical Intervals

• Measure the PR interval (normal: 120-200 ms or 3-5 small squares) to assess AV conduction 1, 2
• Measure QRS duration (normal: <120 ms or <3 small squares) to evaluate ventricular conduction 1, 2
• Calculate QTc using Bazett's formula (normal: <450 ms for men, <460 ms for women) to assess repolarization 1, 2
• Identify any conduction abnormalities such as AV blocks, bundle branch blocks, or pre-excitation 2

Step 4: Determine Electrical Axis

• Examine leads I and aVF to quickly determine the axis quadrant 1
• Normal axis: -30° to +90° (positive in both leads I and aVF) 2
• Left axis deviation: -30° to -90° (positive in lead I, negative in aVF) 2
• Right axis deviation: +90° to +180° (negative in lead I, positive in aVF) 2

Step 5: Analyze Waveform Morphology

P Waves

• Examine P wave morphology (normal: upright in I, II, aVF; biphasic in V1) 1
• Evaluate P wave duration (<120 ms) and amplitude (<2.5 mm) 1
• Assess for atrial enlargement patterns 2

QRS Complexes

• Analyze QRS morphology for pathologic Q waves (>1 mm wide and >1/3 the height of the R wave or >0.04 seconds) suggesting myocardial infarction 1, 2
• Assess R wave progression across precordial leads (amplitude increases from V1 to V4, then decreases toward V6) 1
• Look for voltage criteria for left ventricular hypertrophy: S in V1 + R in V5 or V6 >3.5 mV 2

ST Segments and T Waves

• Examine ST segments for elevation (>0.1 mV in limb leads or >0.15-0.2 mV in precordial leads) or depression that may indicate ischemia or injury 1, 2
• Assess T wave morphology (normally upright in leads I, II, V3-V6; inverted in aVR; variable in III, aVL, aVF, V1, V2) 1
• Look for T-wave abnormalities including inversion, hyperacute changes, or flattening 2

Step 6: Identify Location of Abnormalities

• Note the location of ST-segment or T-wave abnormalities to determine the affected coronary territory 2
• Correlate findings with clinical presentation to assess for acute coronary syndrome 1

Critical Pitfalls to Avoid

• Never rely solely on computer interpretation without physician verification, as computer programs perform less well than expert readers and errors remain common 3, 2
• Avoid misplacement of electrodes, particularly precordial leads, which can significantly alter interpretation and lead to false diagnoses 2
• Do not interpret the EKG in isolation—always consider the patient's clinical presentation, as the same finding may have different implications depending on symptoms 2
• Always compare with previous EKGs when available to identify significant changes 2
• Be aware that inadequate filtering settings can distort waveforms and affect measurements 2

Special Considerations

• Age and gender affect normal EKG parameters—QT intervals are typically longer in women, and QRS voltage criteria decline with age 1, 2
• Certain medications (antiarrhythmics, psychotropics) can affect EKG findings 1
• T waves are often inverted in leads V1, V2, and V3 in children older than 1 month 2
• Athletes may demonstrate normal variants including sinus bradycardia (≥30 beats/min) 2

Quality Assurance

• All computer-based EKG reports require physician overreading, as computer interpretation is only an adjunct to the electrocardiographer 3
• Evaluate the quality of the EKG recording and identify any technical artifacts that may affect interpretation 2
• Consider continuing medical education through seminars or self-assessment programs to maintain current EKG interpretation skills 2