ECG Basics

General

• 1 small box = 1mm = 0.04 sec = 40 miliseconds
• 5 small boxes = 1 big box = 5mm = 0.2 sec = 200 miliseconds
• Entire ECG strip is ~10 seconds

Intervals

Interval	Time (s)	Boxes
PR	0.12 - 0.20	3-5
QRS	.06 - 0.10	1.5-2.5
QTc	<0.44	N/A

Axis

• Cannot be measured if BBBs are present
• If up in leads 1 and AVF then normal axis

Q waves

• Significant if >1 box wide or if is 1/3 of entire QRS amplitude
• Early Repolarization:
  • ST elevation most prominent in lat precord leads (V4-6) but no reciprocal changs
  • T waves usually broad, tall (>5mm) & upright
  • Limb leads may also have ST elevation, rarely >2 mm

T waves

• Normally upright in 1, 2, V3-V6
• Negative in AVR
• If is greater than 2/3 height of R wave then is abnormal
• Deep symmetrical inverted T waves:

1. Left ventricle apical hypertrophy
2. Raised ICP (e.g.SAH)
3. Wellen's (MI)
4. Paced rhythm
5. BBB's or WPW
6. Idiopathic

RAE

• Rarely isolated finding (usually RVH/RAD also)
• P amplitude >2.5mm in II
• Large biphasic p wave in V1
• Right atrial hyper.-initial component is larger in V1 than V6

1. p-mitrale-m notched p wave in leads 1 and 2. Greater than .12 seconds.

RAE

LAE

• Biphasic P in V1 w/ wide, deep terminal component, >1mm depth & wide

1. Left atrial hyper.-terminal component is larger than .04 sec.

LVH

1. Sum of S in V1 or V2 & R in V5 or V6 is >35mm
2. Sum of highest R & deepest S in precord is >45mm
3. R wave in V6 > 18mm
4. R in AVL of >12mm
5. L precordial leads may show ST depression & TWI = LV strain pattern
6. LAD-with slightly wide QRS. Or r in avl greater than 11mm, r in 1 is greater than 12mm, or R in AVf is greater than 20mm

RVH

1. Dominant R in V1 >7mm (also seen in WPW, RBBB, post MI, & nml var)
2. RSR in V1 w/ QRS < 0.12
3. This dx usu also w/ RAE or strain (ST dep w/ twi in V1-V3).
4. Less sens. & spec. than LVH, usu nl ecg
5. RVH-R wave greater than S in V1, but gets progressively smaller from V1 to V6. S wave persists in V5 and V6. RAD with slightly wide QRS.
6. (note: R :S ratio greater than 1 also in: 1.RBBB 2.WPW type A. 3. Post. Wall MI. 4.kids.)

RBBB

1. QRS > 0.12 in limb leads
2. Triphasic QRS (rSR'), often w/ ST depression & TWI in V1-V3
   1. V1 must have a positive complex
3. Slurred S in 1 and V6

LBBB

1. ST depression and TWI are common
2. QRS > 0.12 in limb leads
3. Leads
   1. Large and wide R waves — leads I, aVL, V5, and V6
   2. Small R wave followed by deep S wave —leads II, III, aVF, V1–V3

LAFB

1. Left axis deviation (-45 or more) w/QRS <0.10s
2. Deep S in II, III, and AVF

LPFB

1. Usually means disease
2. Right axis deviation (>110) w/QRS < 0.10s
3. Tall R in II, III, AVF
4. Exclude other causes (COPD, RVH, Lat MI)

Source

9/09 DONALDSON (adapted from Niemann, Lampe, Pani)

Journal of Electrocardiology. Vol 43 (2010). 40-42.