Basic ECG

Components of an ECG Tracing

P

Q S

R

T UJ

PR interval

QRS interval

ST segment

QT interval

Normal Values

P wave <0.12 sec<0.25 mV<0.1 mV terminal negative deflection in V1

PR interval 0.12-0.20 secQRS complex <0.11-0.12 secT wave 5-10 mmQTc = QT/RR

<0.48 sec <0.47 sec

Mnemonic

RRAHIMRate Rhythm Axis Hypertrophy Ischemia Miscellaneous

Rate• “Rule of 300”

• Formula1500 300

# of small boxes # of big boxes

RR interval 1 2 3 4 5 6Heart rate 300 150 100 75 60 50

Rate• 10-second rhythm strip (if the

rhythm is irregular)

# of RR intervals x 6

Rhythm• Sinus P wave?–Upright in leads I and II– Followed by a QRS complex– Inverted in aVR, biphasic in V1

Rhythm• Atrial fibrillation (AF)

• Atrial flutter

Rhythm• Supraventricular tachycardia

(SVT)

Rhythm• Multifocal atrial tachycardia

(MAT)

Rhythm• Ventricular tachycardia

Rhythm• PR interval?– Shortened in WPW and LGL syndromes– Prolonged in 1° or 2° AV block

Rhythm• 1° AV block– Prolonged PR interval

Rhythm• 2° AV block– Type I (Wenckebach)• Progressively lengthening PR interval• (+) Dropped QRS complexes

X X

Rhythm• 2° AV block– Type II• Constant PR interval• (+) Dropped QRS complexes

Rhythm• 3° AV block– Independent atrial and ventricular rates

(AV dissociation)

Axis

Lateral

AnteriorSeptal

Inferior

Axis

I aVFNormal + +Left axis + -

Right axis - +Indeterminate - -

Axis• Formula

90 (aVF)|I| + |aVF|

*If I is negative, add 90.

Normal value (PGH): -30 to 100Normal value (Harrison’s): -30 to 110

Hypertrophy

• Left atrial abnormality (LAA)– P wave ≥3 mm in II OR– Terminal segment of P wave >1 small

box in V1

Hypertrophy

Hypertrophy

• Right atrial abnormality (RAA)– P wave >2.5 mm in II, III or aVF

Hypertrophy

• Biatrial abnormality

Hypertrophy

• Left ventricular hypertrophy (LVH)– S in V1 + R in V5 or V6 >35 mm OR– aVL >11 mm OR

– S in V3 + R in aVL ≥20 mm or ≥28

mm *LV strain: PLUS significant asymmetric ST segment depression w/ broad inverted T wave LVH w/ strain cannot r/o concomitant ischemia

Hypertrophy

Hypertrophy

• Right ventricular hypertrophy (RVH)– RAD + R/S ratio >1 in V1 + R/S ratio

<1 in V6

Hypertrophy

• Biventricular hypertrophy

Ischemia• Myocardial infarction– Significant ST elevation ≥1 mm in limb

leads and ≥2 mm in chest leads OR >0.08 sec

– Significant Q waves ≥25% of QRS complex OR ≥0.04 sec

– Reciprocal leads:• Anterior/anterolateral inferior• Inferior lateral• Lateral anteroseptal

Ischemia• Myocardial infarction

Ischemia• Ischemia– T wave inversion ≥5 mm t/c

ischemia– ST segment depression ≥1 mm in ≥2

contiguous leads ischemia

Miscellaneous• Non-specific ST-T wave changes

– T wave inversion <5 mm– ST segment depression <1 mm– Flattening of ST segment w/o U waves

• Low-voltage QRS complexes– <5 mm in limb leads OR– <10 mm in chest leads

• Poor R wave progression– R wave <3 mm in V1-V3 AND normal R wave in

V4-V6– Exceptions: LVH, LBBB, WPW, anteroseptal wall

MI (absence of R wave in V1-V3), low-voltage QRS

Miscellaneous• Prominent U wave + normal T wave prominent

U wave• Prominent U wave + flattened T wave t/c

hypokalemia• ST segment depression + U wave + normal T wave

cannot r/o ischemia, prominent U wave• Flattened T wave + normal QRS NSSTTWCs• Peaked T waves ≥10 mm in ≥2 contiguous leads

peaked T waves, t/c hyperkalemia• Prolonged QT: type 1A anti-arrhythmics,

hypokalemia, hypocalcemia, hypomagnesemia• NSSTTWCs, prob. digitalis effect: shortened

QT, scooping of ST segment

Miscellaneous

Miscellaneous

• Right bundle branch block (RBBB)– rsR’ pattern in V1 (R wave >15 mm)– Slurred S wave in I and V6

Miscellaneous

• Left bundle branch block (LBBB)– Absent small initial Q waves in LV leads– Positive R wave in LV leads w/ large

secondary R wave–Negative QRS in V1

Miscellaneous

• IVCD: wide QRS not typical of RBBB/LBBB

Miscellaneous

• Early repolarization changes

Miscellaneous

• Premature complexes

Miscellaneous

• Pericarditis

Miscellaneous

• QT interval

QT√RR

*Compute only if the rate is abnormal.

Miscellaneous

• Left anterior hemiblock (LAHB)– LAD– qR complex in I, aVL– rS pattern in II, III, aVF

Miscellaneous

• Left posterior hemiblock (LPHB)– RAD– rS complex in I, aVL– qR complex in II, III, aVF

Thank you!

mer

edith