EKG stuff

QT (corrected)

Rate:

• HR
  • 60 / average RR (in seconds)
  • 1500 / average RR (in mm, or #small boxes)
  • Count from R wave: 300, 150,100, 75, 60, 50
• standard paper speed 25 mm/s
• small square 0.04 s
• large square 0.20 s
• amplitude standard = 10 mm (1 mV)

Rhythm:

• Every P wave is followed by a QRS
• Every QRS is preceded by a P wave
• The P wave axis is between 0 deg and 90 deg
• Up in I,II,AVF, Down in AVR
• The P wave morphology is constant

Axis

• P wave axis
• QRS axis
• T wave axis
• Look in Leads I and aVF
• Left Axis Deviation: TA, AV canal

Intervals

• PR interval: <0.12-0.2 sec (beginning of P to peak of R)
• QRS interval: <0.07-0.1 sec 
• QT interval (QTc): </= 0.44 sec

P-wave (3x3)

• < 0.10 s (less than 3 small boxes)
• < 0.08 s in infants (less than 2 small boxes)
• less than 3 boxes tall, <30 mV (nl standardization)

Atrial Enlargement

• Right: Look at leads II and V1
  • Peaked P (>3mm) if under 6 months
  • Peaked P (>2.5 mm) if over 6 months
• Left: Look at lead II
  • Wide P or notched (“L”umpy), P >0.1 sec

R-wave progression

• from V1-V6: increasing R, decreasing S (representing dominance of L ventricular forces)
• look for dominant S in right precordial leads (V1, V2)
• look for dominant R in left precordial leads (V5, V6)
• Note: infants and newborns have normal dominance of the R ventricle

Q-waves

• less than 1 box (<0.04 s, <1 mm) in duration
• less than 1/4 of total QRS amplitude
• If less than 3 y/o:
  • L precordial leads and AV-F: < 5 mm deep
  • III: <= 8 mm

ST segment

• Myocardial injury indicated by ST segment elevation or depression...
  • Limb leads: more than 1 mm
  • Precordial leads: more than 2 mm
  • IF ST is upsloping, that's called J-depression and it's normal
  • downsloping or parallel: abnormal

T-wave

• peaked in hyperkalemia
• flat or low in hypokalemia, hypothyroid, normal newborn, myocardial/pericardial ischemia/inflammation
• the normal newborn has an upright T-wave in V1, which inverts by 1 week of age. A persistent upright T-wave in an infant signifies R ventricular hypertension (not hypertrophy). The T-wave normally goes back upright in V1 by age 4-6 y/o. Persistence of the inverted T can occur rarely, known as persistence of the juvenile pattern. Since this is rare, an adult with inverted T should have the differential diagnosis worked up, with persistent juvenile pattern a diagnosis of exclusion.
• T-wave axis progression:
  • Newborn: all upright
  • 1 week: V1-V4 downward, V5-V6 remain upright
  • 1 month: V4 flips upright
  • 1 year: V3 flips upright
  • 8 year: V2 flips upright
  • 18 years: V1 flips upright
  • some adults will have downward T wave in V1normally

Hypertrophy

• Atrial: >3 mm tall, more than 0.10 s (3 boxes) wide - in this case you might see a double hump or sine wave.
• RVH: need at least one of the following
  • Increased R and anterior QRS voltage
    • V1: R is >98%ile for age
    • V6: S is >98%ile for age
  • V1: upright T (3 days of age to adolescence)
  • V1: q wave present (qR pattern)
  • Right axis deviation (for patient's age)
  • RV strain (V1 has inverted T and tall R)
  • Also look for: Increased R/S ratio in V1, Decreased in V6
• LVH
  • R wave > 98th percentile in V6 (and I and aVL)
  • S wave > 98th percentile in V1
  • Increased R/S in V6 or decreased in V1
  • Q wave > 5mm in V6 with peaked T wave (septal hypertrophy)
  • Flat/inverted T waves in I or V6 with LVH suggests strain pattern
  • LAD for pt’s age

Repolarization

• ST segment: elevation or depression >1mm in limb leads and >2mm in precordial leads consistent with myocardial injury
• T-wave: (always upright in II, III, aVF and I, V5, and V6)
  • inverted on day 3-5 until adolescence/teenage years (in precordial leads)

Harriet Lane 16th Ed.
CHLA Board Review 2005