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C6 Cardiology and Cardiac Surgery
Approach to ECGs Toronto Notes 2019
• leads◆ standard 12-lead ECG
◆ limb (bipolar) leads: I, II, III, aVL, aVR, aVF
◆ precordial (unipolar) leads: V1-V6 (V1-V2 septal, V3-V4 anterior, V5-V6 lateral)
■ additional leads
◆ right-sided leads: V3R-V6R (useful in RV infarction and dextrocardia)
■ leads that indicate specific regions of the heart: ◆ lateral wall = I, aVL, V5, V6
◆ inferior wall = II, III, aVF
◆ anterior wall= V1-V4
Indications
• detectmyocardialinjury,ischemia,andthepresenceofpriorinfarction
• conditionsassociatedwithpalpitationse.g.WPW,longQT,HCM,heartblock,andbradycardia,etc.
• recording of cardiac rhythm during symptoms, antiarrhythmic drug monitoring
• assessment of cardiac structure and function. Note ECG can indicate hypertrophy, and cardiomyopathy,
etc.
• non-sustainedarrhythmiasthatcanleadtoprophylacticintervention
Contraindications
• noabsolutecontraindicationsexceptpatientrefusalorelectrodelatexadhesiveallergy
Approach to ECGs
Introduction
Below, we are presenting both the Classical Approach and the newer PQRSTU Approach to provide students with different ways to view the ECG. Despite methodological differences, the rigor and final result is the same. These two approaches should help you better understand the concepts of ECG interpretation and equip you with the necessary skills to interpret ECGs in exam scenarios and clinical practice
Classical Approach to ECGs
RATE
• normal=60-100bpm(atrialrate:150-250bpm=paroxysmaltachycardia,250-350bpm=atrialflutter,
Rate Calculations
• Examples, practice
For more examples and practice visit www.ecgmadesimple.com
Classical Approach to ECG
• Rate
• Rhythm
• Axis
• Conduction abnormalities
• Hypertrophy/chamber enlargement • Ischemia/infarction
• Miscellaneous ECG changes
Differential Diagnosis for Left Axis Deviation (LAD)
• Left anterior hemiblock
• Inferior MI
• WPW
• RV pacing
• Normal variant
• Elevated diaphragm
• Lead misplacement
• Endocardial cushion defect
Differential Diagnosis for Right Axis Deviation (RAD)
• RVH
• Left posterior hemiblock
•
• •
>350 bpm = AFib, in AF atrial “rate” not discernible ) regularrhythm
■ to calculate the rate, divide 300 by number of large squares between 2 QRS complexes (there are 300 large squares in 1 min: 300 x 200 msec = 60 sec)
■ or remember 300-150-100-75-60-50-43 (rate falls in this sequence with the number of large squares between 2 QRS complexes)
irregularrhythm
■ rate = 6 x number of R-R intervals in 10 s (the “rhythm strips” are 10 sec recordings)
atrialescaperhythmIcaseofsinusnodefailure=60-80bpm;junctionalescaperhythm=40-60bpm; ventricular escape rhythm = 20-40 bpm
• Pulmonary embolism • COPD
• Lateral MI
• WPW
RHYTHM
• regular:R-Rintervalisthesameacrossthetracing
• irregular:R-Rintervalvariesacrossthetracing
• regularlyirregular:repeatingpatternofvaryingR-Rintervalse.g.AFlutter • irregularlyirregular:R-Rintervalsvaryerraticallye.g.AFib,VFib
• normal sinus rhythm (NSR)
• Dextrocardia • Septal defects
-120°
-150° ±180o
150°
120°
Lead III
Figure 7. Axial reference system
Each lead contains a (+) area displayed by the bold arrows. Impulses traveling toward the positive region of the lead results in an upward deflection in that lead. Normal QRS axis is between -30o and +90o
■ P wave precedes each QRS; QRS follows each P wave
■ P wave axis is normal (positive in 2 out of the 3 following leads I, II, aVF, positive in 1, aVL) ■ rate between 60-100 bpm
AXIS
• meanaxisindicatesthedirectionofthemeanvector
• canbedeterminedforanywaveform(P,QRS,T)
• thestandardECGreportedQRSaxisusuallyreferstothemeanaxisofthefrontalplane–itindicates
the mean direction of ventricular depolarization forces • QRSaxisinthefrontalplane
■ normal axis: -30o to 90o (i.e. positive QRS in leads I and II) ■ i.e. usually east to southeast
■ left axis deviation (LAD): axis <-30o
■ right axis deviation (RAD): axis >90o
• QRSaxisinthehorizontalplaneisnotroutinelycalculated ■ transition from negative to positive is usually in lead V3
aVR
aVL
0° LeadI
-90°
90°
aVF
-60°
30° 60°
Lead II
-30°