How to read an EKG
How to Properly Use and Interpret an Electrocardiogram (EKG/ECG): A Clinician’s Guide
By Shabazz Farrakhan, JD, SJD, ADN
Affiliations: Vanderbilt University School of Medicine, Northwestern Memorial Hospital & Cedars-Sinai Medical Center
Abstract
The electrocardiogram (EKG or ECG) remains an indispensable, non-invasive diagnostic tool for the assessment of cardiac electrophysiology. It is foundational in the evaluation of arrhythmias, ischemia, electrolyte imbalances, and structural heart pathology. As both a practitioner and clinical educator affiliated with three world-class institutions, I’ve witnessed first-hand how precision in EKG acquisition and interpretation often distinguishes the exceptional from the average clinician. The objective of this article is to provide a refined, systematic protocol for using an EKG effectively — not just as a diagnostic machine, but as a direct window into the myocardial narrative.
Introduction
An EKG is a graphical representation of the electrical activity of the heart captured via skin-surface electrodes. It translates ionic movements into visual waveforms across 12 standard leads, reflecting depolarization and repolarization across specific cardiac vectors. Every clinical context, from emergent care to routine outpatient screening, can benefit from a sound understanding of EKG mechanics and interpretation.
1. Proper Electrode Placement:
Preparation
Ensure clean, dry skin free of oils or hair at electrode sites. Use alcohol wipes and shave areas if necessary.
Position the patient supine with arms relaxed at their sides and legs uncrossed.
Limb Leads (RA, LA, RL, LL):
RA (right arm): just below the clavicle, right side
LA (left arm): just below the clavicle, left side
RL (right leg): just above the right hip
LL (left leg): just above the left hip
Precordial Leads (V1–V6):
V1: 4th intercostal space, right sternal border
V2: 4th intercostal space, left sternal border
V3: midway between V2 and V4
V4: 5th intercostal space, midclavicular line
V5: anterior axillary line, horizontal to V4
V6: midaxillary line, horizontal to V5
Proper placement ensures accurate waveform morphology and amplitude, especially critical in identifying myocardial infarctions and bundle branch blocks.
2. Machine Operation & Quality Control:
Input patient demographics (name, DOB, MRN) to ensure traceability.
Confirm paper speed (25 mm/s) and calibration (1 mV = 10 mm) to maintain standardized interpretation.
Instruct the patient to breathe normally but remain still during acquisition. Motion or muscle artifact can obscure key features like P waves or ST segments.
Run a baseline calibration test strip if the machine permits.
3. Interpretation: A Systematic 6-Step Approach
Step 1: Rate and Rhythm:
Use the 300 / large box method or count QRS complexes in a 6-second strip x10.
Identify regularity, P-wave morphology, and PR intervals to diagnose sinus rhythm or arrhythmias (e.g., atrial fibrillation, flutter, junctional rhythms).
Step 2: Axis:
Evaluate leads I and aVF.
Look for left axis deviation (e.g., LVH, left anterior fascicular block) or right axis deviation (e.g., PE, right ventricular strain).
Step 3: Intervals:
PR (120–200 ms), QRS (<120 ms), QTc (<440 ms men, <460 ms women)
Prolongation or shortening may indicate electrolyte abnormalities, drug effects, or congenital conditions.
Step 4: Hypertrophy and Enlargement:
P pulmonale (RAE), P mitrale (LAE), Sokolow-Lyon index for LVH
R/S ratio in V1/V6 for RVH
Step 5: Ischemia or Infarction:
ST elevations (>1 mm in 2 contiguous leads): suspect STEMI
Reciprocal changes, Q waves, and T-wave inversions: localize infarction zone (anterior, inferior, lateral, posterior)
Step 6: Miscellaneous Patterns:
U waves, Brugada patterns, WPW delta waves, prolonged QT syndromes
Always correlate clinically and consider further diagnostics (e.g., echo, troponins)
Common Clinical Pitfalls
Incorrect lead placement mimicking pathology (e.g., reversed limb leads simulating axis deviation).
Failure to repeat EKG after correcting artifacts.
Over-reliance on machine interpretation: computerized readings should never supersede clinical reasoning.
Conclusion:
Mastering the EKG is a mark of a clinician who respects both the heart’s physiology and the art of diagnostics. As physicians trained in the cross-disciplinary intersection of acute medicine, legal medical analysis, and frontline clinical response, we must view the EKG not merely as a rhythm check — but as a biomedical narrative, told in intervals, deflections, and patterns.
Author’s Note:
> “Whether at Cedars-Sinai’s cardiac cath lab, a Vanderbilt Grand Rounds, or a trauma bay at Northwestern, the EKG has saved more lives than we could ever count. It demands fluency, not familiarity.”
— Shabazz Farrakhan, JD, SJD, ADN
