• Name, date, time, paperspeed (25mm/s), scale (10mm/mV)

    • Small square = 0.04 seconds (40ms)

    • Large square (5mm) = 0.2 seconds (200ms)

  • Look for Lead placement errors

    • Lead V1 and V2 at 4th ICS, V4 at 5th ICS mid-clav, V6 mid axillary line

      • Look for RS pattern in V1 changing progressively to QR pattern in V6

    • aVF (left leg = Red), aVL (left arm = black), avR (right arm = white)

      • Check aVR for flipped P, QRS, T waves

      • aVL and aVR should generally be mirror images

  • Clinical context (age, time, patient symptoms)

  • Compare with previous

Rate (60-100)

  • R-R

    • 1 large square = 300/minute (5 large squares per second)

    • 2 = 150 | 3 = 100 | 4 = 75 | 5 = 60 | 6 = 50 |7 = 40

  • Or calculate 10*QRS complexes in 15cm (= 6 seconds x 25mm/s)


  • Sinus (P followed by QRS)

  • Narrow QRS tachycardia (SVT):

    • Sinus tachycardia

    • A fib

    • A flutter (often 300/min with 2:1, 3:1, 4:1 block)

    • AVNRT (regular 180-250/min)

  • Wide complex tachychardia (QRS>120ms)

    • If VERY wide (QRS>200ms) think TOX or METABOLIC

      • Try Calcium (hyperK) and Bicarb (acidosis) first!

    • V tachycardia

    • SVT with aberrancy

    • V fib

  • Bradycardia

    • 1st degree AV block (PR>200ms)

    • 2nd degree AV block type I (Wenkebach)

      • PR prolongation until block

    • 3rd degree AV block (complete block /AV dissociation)

    • Ventricular escape rhythm (wide complex <40/min)

Conduction intervals

  • PR interval (ie. PQ) normally 120-200ms (3-4 small squares)

    • PR >200ms = AV node delay

    • PR <120ms = pre-excitation (LGL) or AV nodal (junctional) rhythm

    • PR <120ms + delta-wave = WPW (risk of AVRT)

  • QRS complex normally < 120ms (3 small squares)

  • QT interval varies with heart rate

    • Prolonged >450ms in electrolyte abnormalties (hypokalemia) or drugs

      • QTc > 500ms Risk of V fib


  • Quadrant/Three Lead Method

    • Lead 1 Positive, Lead aVF Positive = Normal Axis

    • Lead 1 Positive, Lead aVF Negative

      • Lead II equiphasic = Physiological LAD

      • Lead II Negative = Pathological LAD

        • LVH, LBBB, Inferior MI, WPW

    • Lead 1 Negative, Lead aVF Positive = RAD

      • eg. RVH. RV strain (PE), Lateral MI, WPW

    • Lead 1 Negative, Lead aVF Negative = Extreme Axis

      • eg. Ventricular rhythm, hyperkalemia, severe RVH


  • P wave (look at lead II)

    • Normally positive in I and II, bifasic in V1, similar shape in every beat

      • Otherwise, consider ectopic atrial rhythm

  • QRS

    • Pathologic Q-wave (MI, cardiomyopathy, WPW, LBBBB, COPD, PE, lead placement)

      • Q width >1mm (1 small box) OR 1/3 QRS amplitude OR any in V1-V3

    • RBBB

      • rR' or rSR' in V1

      • Large S wave in V6

    • LBBB

      • QS or RS in V1

      • Large R wave in V6

    • LAFB

      • Q1S3

    • LPFB

      • S1Q3

    • RVH

      • R>S in V1

      • S wave in V6

    • LVH

      • S in V1 + [R in V5 or V6 ] ≥35mm (7 large boxes)

      • R in aVL≥11mm

  • ST

    • Elevation

      • Ischemia, percarditis, LVH, benign

    • Depression

      • Reciprocal in ischemia, LVH strain, digoxin

    • Negative T wave (opposite QRS complex)

      • Consider subendocardial ischemia, LVH

  • U wave (small wave after T wave best seen V2-V3)

    • Prominent U wave if >1-2mm or 25% height of T wave

      • Bradycardia

      • Severe hypokalemia

      • Other electrolyte abnormalities (hypercalcemia), thyrotoxicosis, drug

    • Inverted U wave

      • Specific sign of MI

Do NOT Miss!

Need for PCI

  • STEMI (or equivalent need for urgent repurfusion)

    • ST segment elevations at J point in 2 contiguous leads

      • Men <40yo, ≥2.5 mm in V2 and V3 and 1 mm in all other leads

      • Men >40yo, ≥2 mm in leads V2 and V3 and 1 mm in all other leads

      • Women, ≥ 1.5 mm ST elevation in V2 and V3 and 1 mm in all other leads

    • Left bundle branch block and presentation consistent with ACS

      • Unstable patient (hypotensive, acute pulmonary edema, electrical instability, unwell)

      • Modified Sgarbossa criteria can help if LBBB or paced, at least one of the following

        • ≥ 1 lead with ≥1 mm of concordant ST elevation

        • ≥ 1 lead of V1-V3 with ≥ 1 mm of concordant ST depression

        • ≥ 1 lead anywhere with ≥ 1 mm STE and proportionally excessive discordant STE, as defined by ST/S ratio ≥ 25% of the depth of the preceding S-wave.

    • New Right Bundle Branch Block with Left Anterior Fascicular Block (RBBB+LAFB)

      • Look for ST elevations, but can be difficult to discern (must identify end of QRS)

    • Inferior Wall MI

      • Elevation (even < 1mm) in two contiguous leads (II, III, aVF) with any amount of ST segment depression in aVL

        • If there are well developed QS-waves, it is likely to be old MI with persistent ST elevation.

        • LV aneurysm, LVH, WPW, and LBBB all have repolarization abnormalities that produce reciprocal ST depression in aVL.

        • If these are not present, ST depression in aVL is highly sensitive and specific for acute inferior MI.

    • RV MI

      • RV MI usually has ST elevation in V1 UNLESS there is concomitant ST depression in V2 (posterior MI which attenuates the STE in V1)

      • Consider V3R and V4R elevation ≥ 0.5 mm increases specificity

    • Posterior MI

      • Precordial ST-depression ≥ 1 mm maximal in leads V1-V4.

        • Tall R and upright T

      • Consider V8 and V9 elevations ≥ 0.5 mm increases specificity, but not sensitive

    • High Lateral Wall MI

      • Any degree of ST elevation in aVL with ST depressions in lead III (with or without II and aVF)

    • de Winter ST/T-wave complex (hyperacute T-wave with depressed ST takeoff)

      • ST depression >1mm upsloping at the J-point in V1-V6

      • Tall T-waves and Normal QRS duration (consider hyperkalemia if wide QRS)

    • Diffuse ST Depressions with aVR Elevation (left-main or LAD or multivessel disease)

      • May want to avoid dual-antiplatelet therapy if expecting multivessel disease and need for CABG

      • Note: PE, aortic dissection can cause aVR elevation

  • Non-STEMI

    • ST segment depressions or deep T wave inversions without Q waves or possibly no ECG changes

  • High risk of STEMI

    • Wellens/LMCA syndrome (classically pain free, low/normal trop)

      • Pattern A is biphasic T-wave (Up and then Down)

      • Pattern B is deeply inverted T-waves

    • Transient STEMI

  • Unstable Angina

    • No EKG changes

  • FALSE positive ST elevation (eg. LVH)

Early reciprocal changes, suspect ACS

  • New tall upright T wave or biphasic T wave in V1

    • T wave V1>V6 (except in LVH, LBBB)

  • Lone T wave inversion in aVL (except in LVH, LBBB), predict inferior MI


Brugada's Syndrome

  • Common in men from Southeast Asia

  • Prominent J-wave with downsloping ST elevation in leads V1-3 (Saddle-back vs Coved appearance)

Long QT Syndrome

  • Risk of torsade de pointes and ventricular fibrillation if QTc >500ms

  • QTc = QTm / [R-R]

  • Treatment

    • Avoid QT-prolonging drugs, high-intensity sports

    • Cardiology referral

    • B-blocker as prophylaxis

Wolff-Parkinson-White (WPW) syndrome

  • PR<120ms

  • Delta wave (slurring of initial QRS)

  • QRS>110ms

  • May present in very fast atrial fibrillation with irregular QRS


  • Tall T waves, wide QRS, flat P waves

  • Bradyarrhythmia (sinus bradycardia, slow AF, AV block)

  • Sine wave (pre-terminal rhythm)

Sodium Channel Blockade (TCA, cocaine, local anesthetics, propanolol)

  • QRS >100ms (or 2.5 small squares)

  • Terminal or secondary R wave (R') in aVR >3mm

  • R'/S ratio in aVR >0.7

Digoxin Toxicity

  • Increased atrial automaticity (atrial tachycardia, ectopics, AF, flutter)

  • Increased ventricular automaticity (VEB, bigeminy, polymorphic VT)

  • AV blocks

Hypertrophic Cardiomyopathy (HCM)

  • High amplitude QRS

    • Deep, narrow (dagger) Q waves in lateral (V5-6, I, aVL) and inferior (II, III, aVF) leads

  • Suspect clinically

    • Exertional syncope/pre-syncope

    • Pulmonary congestion (orthopnea, PND)

    • Chest pain, palpitations

  • Management

    • Send for doppler echo

Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC)

  • Epsilon wave, T wave inversions, Prolonged S-wave upstroke

  • QRS widening V1-V3

  • Paroxysmal V tach with LBBB morphology