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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
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