How to Read an EKGHow to Read an EKG

Jason Ryan, MDJason Ryan, MD

Intern ReportIntern Report

How to read an EKGHow to read an EKG

1.1. Rate and RhythmRate and Rhythm how fast/slowhow fast/slow regular/irregularregular/irregular wide/narrowwide/narrow

2.2. Axis and IntervalsAxis and Intervals PR, QRS, QTPR, QRS, QT

3.3. HypertrophyHypertrophy LAE/RAELAE/RAE LVH/RVHLVH/RVH

4.4. ST Changes and Q wavesST Changes and Q waves

How to read an EKGHow to read an EKG

RateRate

300150

10075

6050

40

How to read an EKGHow to read an EKG

Axis QRSAxis QRS

0o

90o

-90o

-180o

RAD

LAD

Normal Axis

Lead I (-) (+)

Lead

aV

F (

+)

(-)

How to read an EKGHow to read an EKG

IntervalsIntervals

PR0.14-0.21

QRS0.7-011

QTc<0.46

Correct QT

1. QTc=QT/(RR)1/2 (Bazett)

2. QTC=QT + 0.00175(HR-60) (Hodges)

How to Read and EKGHow to Read and EKG

Atrial Atrial EnlargementEnlargement

How to Read and EKGHow to Read and EKG

Ventricular Ventricular EnlargementEnlargement

Sinus RhythmSinus Rhythm

Rate between 60 to 100Rate between 60 to 100

P wave before every QRSP wave before every QRS– Smooth contourSmooth contour– Either all positive or all negative except V1Either all positive or all negative except V1– <0.12s and <0.2mv<0.12s and <0.2mv

Upright P waves in I, II, aVFUpright P waves in I, II, aVF

Negative P wave in aVRNegative P wave in aVR

Limb Lead ReversalLimb Lead Reversal

Right and Left arm reversedRight and Left arm reversed– P wave positive aVRP wave positive aVR– P wave negative aVL and IP wave negative aVL and I– Limb leads look normalLimb leads look normal

Right arm and Right leg reversedRight arm and Right leg reversed– P wave positive aVRP wave positive aVR– P wave negative I, LP wave negative I, L– Lead II isoelectric (almost no QRS)Lead II isoelectric (almost no QRS)

Left Bundle Branch BlockLeft Bundle Branch Block

Criteria:Criteria:– QRS > 120ms (3 small boxes)QRS > 120ms (3 small boxes)– Broad, notched, or slurred R waves in I, aVL, and V5-Broad, notched, or slurred R waves in I, aVL, and V5-

V6V6– Secondary ST-T changes in I, aVL, and V5-V6Secondary ST-T changes in I, aVL, and V5-V6– Absence of Q waves in I, V5-V6Absence of Q waves in I, V5-V6– R-wave peak time >60ms (1.5 small boxes) V5-V6R-wave peak time >60ms (1.5 small boxes) V5-V6

Separate criteria for STE AMISeparate criteria for STE AMI

Right Bundle Branch BlockRight Bundle Branch Block

Criteria:Criteria:– QRS >120ms (3 small boxes)QRS >120ms (3 small boxes)– R’ in the right precordial leads with R’>RR’ in the right precordial leads with R’>R– Secondary ST-T changes in R precordial Secondary ST-T changes in R precordial

leadsleads

Supporting findings:Supporting findings:– Slurred S wave in I, aVL, left precordial leadsSlurred S wave in I, aVL, left precordial leads

Usual criteria for STE AMI applyUsual criteria for STE AMI apply

Left Ventricular HypertrophyLeft Ventricular Hypertrophy

SSV1orV2V1orV2+ R+ RV5orV6V5orV6>35mm >35mm

– >40 if 30-40yrs old>40 if 30-40yrs old– >60 if 16-30yrs old>60 if 16-30yrs old

RRaVLaVL>11mm>11mm

RRII + S + SIIIIII >25mm >25mm

RRaVLaVL + S + SV3V3 >28mm(men) or 20mm(wmn) >28mm(men) or 20mm(wmn)

Left Ventricular HypertrophyLeft Ventricular Hypertrophy

Associated ST-T wave abnormalitiesAssociated ST-T wave abnormalities– STD and TWI in V5-V6STD and TWI in V5-V6

Leads where QRS is mainly positiveLeads where QRS is mainly positive

– Slight STE with upright T in V1-V2Slight STE with upright T in V1-V2Leas where QRS is mainly negativeLeas where QRS is mainly negative

Sinus TachycardiaSinus Tachycardia

All sinus rhythm criteriaAll sinus rhythm criteria– P before every QRSP before every QRS– Upright P in I, II, aVFUpright P in I, II, aVF– Inverted P aVRInverted P aVR

Rate >100Rate >100

T Wave InversionsT Wave Inversions

Indicative of subendocardial or evolving ischemiaIndicative of subendocardial or evolving ischemia

Can be a normal variant in several leads or in the presence of BBBCan be a normal variant in several leads or in the presence of BBB

Can be caused by several other conditionsCan be caused by several other conditions

– Hypertrophic obstructive cardiomyopathyHypertrophic obstructive cardiomyopathy

– Intracranial processes (hemorrhage)Intracranial processes (hemorrhage)

– Medications or electrolyte abnormalitiesMedications or electrolyte abnormalities

– Myocarditis/pericarditis or pulmonary embolismMyocarditis/pericarditis or pulmonary embolism

ST depressionsST depressionsHorizontal ST depressions Horizontal ST depressions are strongly suggestive of are strongly suggestive of ischemia in the appropriate ischemia in the appropriate clinical settingclinical settingDon’t necessarily localizeDon’t necessarily localize– Stress testingStress testing– Reciprocal changesReciprocal changes

Several other conditions can Several other conditions can provoke ST depressions:provoke ST depressions:– LVHLVH– Medications or Medications or

electrolyteselectrolytes– Bundle Branch BlockBundle Branch Block– Pulmonary embolismPulmonary embolism

ST ElevationsST Elevations

Localizes best of all Localizes best of all ischemic EKG changesischemic EKG changes

Usually indication of acute Usually indication of acute myocardial injury (occluded myocardial injury (occluded artery)artery)

Several conditions can also Several conditions can also cause ST elevations:cause ST elevations:– PericarditisPericarditis– Early repolarizationEarly repolarization– LBBBLBBB– LVHLVH

ST Elevation MIST Elevation MI

Evolution of EKG changesEvolution of EKG changes

Normal Acute Hours 1-2 Days 3-7 Days > 7 Days

Leads go togetherLeads go together

Anterior

Leads go togetherLeads go together

Lateral

Leads go togetherLeads go together

Inferior