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    ECG Glossary

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    Features of Normal ECGs
    P wave
    • Duration: 80-110ms
    • Morphology: Upright in I, II; upright or inverted in aVF; inverted or biphasic in III, aVL, V1, V2.
    • Amplitude: <2.5mm
    • In lead V1, positive deflection <1.5mm and negative deflection <1mm
    PR interval
    • Duration 120-200ms
    QRS complex
    • Duration 60-100ms
    • Axis: -30&deg to +90&deg
    • Normal Q waves: small (<40ms in duration and <2mm in height, in most leads)
    ST segment
    • Usually isoelectric (flat) but may vary by approximately 1mm above or below.
    T wave
    • Morphology: Upright in I, II, V3-V6. Inverted in aVR and V1. Maybe be upright, flat, or biphasic in other leads.
    • Amplitude: Usually <6mm (limb leads) or <10mm (precordial leads)
    QT interval
    • Corrected QT interval (QTc) duration: 300-460ms
    • To calculate QTc: QTc = QT/sqrt(RR interval)

    Atrial Rhythms
    Sinus rhythm
    • Normal P wave morphology and axis
    • Every P wave is followed by a QRS complex, and vice-versa
    • Atrial rate is 60-100 bpm and regular
    Sinus arrythmia
    • Normal P wave morphology and axis
    • Gradual change in PP interval
    • Longest and shortest PP intervals vary by >160ms or 10%
    Sinus bradycardia
    • Normal P wave
    • Rate <60 bpm
    Sinus tachycardia
    • Normal P wave
    • Rate >100 bpm
    Atrial premature complexes (APC)
    • Conducted: Abnormal P wave that is premature relative to normal PP interval, and QRS complex is similar in morphology to QRS complex present during sinus rhythm.
    • Non-conducted: Premature and abnormal P wave that is not followed by a QRS complex.
    • With aberrant intraventricular conduction: Premature P wave followed by a QRS with abnormal morphology.
    Atrial tachycardia
    • P wave axis or morphology different from sinus node
    • Three or more beats in succession at a rate of 100-180 bpm (up to 240)
    • Regular rhythm
    • Normal QRS follows each P wave
    Supraventricular tachycardia (SVT)
    • Regular rhythm, rate >100 bpm
    • P wave not easily identified
    Atrial flutter
    • Rapid regular atrial undulations at 240-340 per minute
    • Typical atrial flutter morphology usually present in the inferior leads II, III, and aVF (”sawtooth” appearance)
    • QRS complex may be normal or aberrant
    Atrial fibrillation
    • P waves absent
    • Atrial activity is totally irregular, causing random oscillation of the baseline.
    • Ventricular rhythm is irregular.

    Ventricular Rhythms
    Ventricular premature complexes (PVC)
    • Uniform: A wide QRS complex that is premature relative to the normal RR interval and not preceded by a P wave; morphology of VPC’s is the same.
    • Multiform: VPC’s with >1 morphology
    Ventricular tachycardia
    • Succession of 3 or more premature ventricular beats at a rate of >100 per minute.
    • RR interval is usually regular but may be slightly irregular at its initiation.
    Ventricular fibrillation
    • Rapid, irregular, and chaotic ventricular rhythm with undulating baseline and no distinct QRS complexes.

    P wave abnormalities
    Left atrial enlargement
    • In lead V1, biphasic P wave with a large and wide terminal portion (1 box wide and 1 box deep).
    • In lead II, a humped P wave with >40ms between the first and second atrial components (humps).
    Right atrial enlargement
    • Biphasic P wave in lead V1, with the first (positive) component larger than the second (negative), or
    • P wave height larger than 2.5mm in any limb lead

    AV Conduction Abnormalities
    AV block, 1st degree (1&deg)
    • PR interval >200ms (may be as long as 800ms)
    • Each P wave followed by a QRS complex.
    AV block, 2nd degree (2°) - Mobitz type I (Wenckebach)
    • Progressive prolongation of the PR interval and shortening of the RR interval until a P wave is blocked (i.e. not followed by a QRS complex)
    AV block, 2nd degree (2°)- Mobitz type II
    • Regular sinus or atrial rhythm with intermittent nonconducted P waves
    • PR intervals in the conducted beats are constant.
    AV block, 2:1
    • Regular sinus or atrial rhythm with two P waves for each QRS complex (i.e. every otehr P wave is nonconducted)
    • Note: Can be Mobitz type I or II 2nd degree AV block.
    AV block, 3rd degree (3&deg)
    • Atrial and ventricular rhythms are independent of each other.
    • Atrial rate is usually faster than the ventricular rate.

    Intraventricular conduction defects
    Left bundle branch block (LBBB)
    • Prolonged QRS duration (>120 ms)
    • Broad R waves in leads V5 and V6 that are usually notched or
    • Dominant S wave (either rS or QS) in V1 and/or V2
    • Note:
      • LBBB interferes with determination of QRS axis and ECG diagnoses of ventricular hypertrophy and acute MI.
    Right bundle branch block (RBBB)
    • Prolonged QRS duration (>120 ms)
    • Secondary R wave (R’) in leads V1 and V2, with R’ usually taller than the initial R wave.
    • Wide S wave in lead 1
    • Note:
    • RBBB does not interfere with the ECG diagnosis of ventricular hypertrophy of acute MI.
    • In RBBB, mean QRS axis is determined by the initial unblocked 60-80ms of the QRS, and it should be normal unless left fascicular blocks are present.

    Abnormalities of QRS voltage
    Low voltage
    • Limb leads only: Amplitude of the entire QRS complex (R+S) <5mm in all limb leads.
    • Limb and precordial leads: Amplitude of the entire QRS complex (R+S)<5mm in all limb leads and <10mm in all precordial leads.
    • Possible causes include: chronic lung disease, pericardial effusion, obesity, pleural effusion, restrictive cardiomyopathies, etc.

    Abnormalities of QRS axis
    Left axis deviation
    • Mean QRS axis is >-30°
    • Possible causes include: LBBB, LVH, inferior wall MI, etc.
    Right axis deviation
    • Mean QRS axis is >90°
    • Possible causes include: RVH, dextrocardia, lead reversal, etc.

    Ventricular hypertrophy
    Left ventricular hypertrophy (LVH), by voltage criteria
    • Cornell criteria: R wave in aVL + S wave in V3
      • >24mm in males
      • >20mm in females.
    • Precordial leads: R V5 or V6 + S V1 > 35mm
    • R aVL
      • > 11mm in males
      • > 9mm in females
    Repolarization abnormalities in LVH
    • T wave abnormalities (flipped/inverted), usually seen in leads I, aVL, V5, and V6
    Right ventricular hypertrophy (RVH)
    • Right axis deviation (mean QRS axis >90&deg) or
    • R wave > S wave in lead V1 or
    • R wave > 7mm in lead V1
    Repolarization abnormalities in RVH
    • T wave abnormalities (flipped/inverted) in V1-V3

    Myocardial infarction (MI)
    MI — General considerations
    • Abnormal Q waves
    • Duration >30ms for most leads (>40ms in leads III, aVL, aVF, and V1)
    • Indicates necrosis
  • ST segment elevation (acute myocardial injury)
    • >1-2mm elevation in two more more contiguous leads
    • Usually upwardly convex
    • Can last 48 hours to 4 weeks after MI
  • T wave inversions
    • Indicates ischemia
    • May persist indefinitely
  • Determining age of infarct from ECG:
    • Acute MI: Abnormal Q waves, ST elevation.
    • Recent MI: Abnormal Q waves, isoelectric ST segments, inverted T waves.
    • Old MI: Abnormal Q waves, isoelectric ST segments, normal T waves.
  • Myocardial infarction vs. ischemia
    • Infarction: Abnormal Q waves; ST segment elevation or depression; T waves inverted, normal, or upright.
    • Ischemia: ST segment depression; T wave inversion; Q waves absent.
    Anterolateral infarction, recent or acute
    • ST segment elevation in leads V1-V6
    • Abnormal Q waves (occur approximately 1 hour after onset)
    Anterior infarction, recent or acute
    • ST segment elevation in leads V1-V4
    • Abnormal Q waves (occur approximately 1 hour after onset)
    Anteroseptal infarction, recent or acute
    • ST segment elevation in leads V1-V3
    • Abnormal Q waves (occur approximately 1 hour after onset)
    Lateral infarction, recent or acute
    • ST segment elevation in leads I and aVL
    • Abnormal Q waves (occur approximately 1 hour after onset)
    Inferior infarction, recent or acute
    • ST segment elevation in at least two of leads II, III, aVF.
    • Abnormal Q waves (occur approximately 1 hour after onset)
    Posterior infarction, recent or acute
    • R wave in V1 and V2 (Q waves from the opposite side)
    • R wave > S wave
    • ST segment depression in V1 and V2
    Anterolateral infarction, age undetermined or old
    • Same as recent/acute, but no ST segment elevation.
    Anterior infarction, age undetermined or old
    • Same as recent/acute, but no ST segment elevation.
    Anteroseptal infarction, age undetermined or old
    • Same as recent/acute, but no ST segment elevation.
    Lateral infarction, age undetermined or old
    • Same as recent/acute, but no ST segment elevation.
    Inferior infarction, age undetermined or old
    • Same as recent/acute, but no ST segment elevation.
    Posterior infarction, age undetermined or old
    • Same as recent/acute, but no ST segment elevation is characteristic of acute posterior injury.

    QT interval abnormalities
    Long QT interval
    • Corrected QT interval (QTc) >420-460ms.
    • (QTc = QT divided by the square root of the preceding RR interval)
    Long QT syndrome
    • QT interval more than half of the cardiac cycle.

    Clinical disorders
    Digitalis effect
    • Sagging ST segment depression with upward concavity (”scooped out” ST)
    Digitalis toxicity
    • Can cause almost any type of cardiac arrhythmia, except bundle branch blocks.
    • Typical abnormalities include: atrial and junctional premature beats, atrial fibrillation with complete heart block, 2nd or 3rd degree AV block, supraventricular tachycardia, etc.
    Hyperkalemia
    • Moderate (K+ = 5.5-7.5 mEq/L):
    • Tall, peaked T waves
    • Wide, flattened P waves
    • QRS widening
  • Extreme (K+ > 7.5 mEq/L):
    • Disappearance of P waves
    • Markedly widened QRS
    Hypokalemia
    • Prominent U waves
    • Flattened T waves
    • ST segment depression
    Hypercalcemia
    • QT shortening
    Hypocalcemia
    • Prolonged QT segment
    Sick sinus syndrome (SSS)
    • Can include one or more of the following:
    • Marked sinus bradycardia
    • Bradycardia alternating with tachycardia
    • Atrial fibrillation
    • Others…