Review of EKG Interpretation

Basics of Interpretation

• Limb leads

• Precordial leads

• Atrial and ventricular depolarization and contraction in relation to the EKG waveforms

Rate

• Evaluate the distance between R-R intervals.

• 1 small box = 0.04s

• 1 large box = 0.2s

• Counting based off of large boxes:

• Irregular rhythms (or very slow/fast): ​

• 6 second strip: # cycles × 10 = rate​

• 10 second strip: # cycles × 6 = rate​

• Rate > 100 = tachycardia​

• Rate < 60 = bradycardia

Rhythm

• Identify Basic Rhythm

• Evaluated for pauses, premature beats, irregularity, abnormal waves

• Always check for:

• P waves before each QRS complexes

• PR intervals to determine AV blocks

• QRS intervals to determine bundle branch blocks

• QT intervals to evaluate for risk for Torsade's and to limit / discontinue any QT prolonging medications

Axis

• Normal Sinus Rhythm

• Regular rate - 60-100bpm

• P wave before each QRS

• Normal P wave Axis

• PR interval constant

• QRS <120ms

• Sinus Bradycardia

• Sinus rhythm criteria with rate < 60 bpm​

• Sinus Tachycardia

• Sinus rhythm criteria with rate > 100 bpm

• SVT​

• Any tachycardia above bundle of His, but commonly used to describe AVNRT​

• Regular​ Rate ~140-280​

• Narrow QRS (< 120 ms) ​

• P waves can have retrograde conduction or inversion​

• Atrial Fibrillation​

• Irregularly irregular ​

• No P waves​

• Variable ventricular rate​

• QRS usually narrow, < 120 ms unless other BBB, accessory, aberrancy ​

• Fibrillatory waves

• Atrial Flutter​

• Atrial activity ~300 bpm​

• Narrow QRS < 120 ms​

• “Saw tooth” inverted flutter waves in inferior leads​.

• Ventricular rate a fraction of atrial rate

• 2:1 block = 150 bpm

• 3:1 block = 100 bpm

• 4:1 block = 75 bpm

• Ventricular Tachycardia​

• Wide and broad complex tachycardia​

• Uniform QRS complexes in each lead

• Ventricular Fibrillation​

• Chaotic irregular deflections​

• No P waves, QRS, T ​

• Amplitude rate 150-500 ​

• Amplitude decrease with duration (coarse to fine)

• AV Blocks​

• First Degree Block

• Fixed PR interval elongation (>200ms)

• Second Degree block Mobitz Type I​ (Wenckebach)

• Progressive prolongation of the PR interval until a non-conducted P wave

• Second Degree block Mobitz Type II​

• Intermittent non-conducted P waves without progression of PR interval

• Third Degree​ block

• AV dissociation​

• Independent atrial and ventricular rates

• Myocardial injury morphologies

• Ischemia

• Inverted T waves (symmetrical inversion)

• Usually in same lead that demonstrates acute infarction ​

• ST depression can represent subendocardial ischemia

• Injury

• ST elevation​

• Represents an acute process (normalizes over time)​

• Acute or recent infarct can presents with significant Q waves

• Infarct / Necrosis

• Significant Q wave​

• > 1 mm wide or 1/3 amplitude of QRS​

• Significant Q waves can remain over time (permanent)

Advanced ECG Interpretations

• sinus arrhythmia, wandering pacemaker, MAT, torsades

• Ectopy​

• Ventricular Hypertrophy​

• Atrial enlargement​

• Electrolyte abnormalities​

• Sinusoidal waves

• hyperacute T waves

• u waves

• Fascicular blocks/hemi-blocks​

• Aberrant conduction patterns​

• Brugada criteria​

• Wolf-parkinson-white

• Epsilon waves

• OMI (occlusive myocardial infarctions) vs. STEMI paradigm shift

• Sgarbossa criteria​

• Wellen's waves

• DeWinter T waves

• RV infarction

• Posterior MI

• Diffuse ST depression

• Wide based peaked T waves

• Medication effects

• TCAs

• Digoxin

References

• Cadogan, Mike. “ECG Lead Positioning.” Life in the Fast Lane • LITFL, 30 Jan. 2022, litfl.com/ecg-lead-positioning/. ​

• Cadogan, Mike. “ECG Library.” Life in the Fast Lane • LITFL, 14 Nov. 2021, litfl.com/ecg-library/. ​

• Cummins, Richard O., et al. ACLS Provider Manual. American Heart Association, 2004. ​

• Dubin, Dale. Rapid Interpretation of EKG’s: Dr Dubin’s Classic, Simplified Methodology for Understanding EKG’s. Cover Publishing, 2016.

John Coacci, DO