ECG Basics

General

• 1 small box = 1mm = 0.04 sec = 40 miliseconds
• 5 small boxes = 1 big box = 5mm = 0.2 sec = 200 miliseconds

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

1. Anterior hemiblock-left axis deviationgreater than-45 to -60. and small q in 1 and avl. RS in 2,3, avf. Intrinsicoid deflection in avl greater than .045.
2. posterior hemiblock-right axis deviation and S1Q3.
3. Find isoelectric lead. Axis is perpendicular.
4. Horizontal axis-find isoeletric chest lead. If shifted to V1 or V2 then counterclockwise rotation. If shifted to V5 or V6 then clockwise rotation.

Q waves

1. sig Q waves are @ least 1 mm (1 box) wide or @ least 1/3 of the entire QRS amplitude.
2. Early Repolarization:
   1. STE most prominent in lat precord leads (V4-6) but no reciprocal chngs. T waves here usu broad, tall (usu > 5mm) & upright.
   2. limb leads may also have ste, rarely >2 mm

T waves

1. T waves are normally upright in 1,2,V3 to V6. Negative in AVR.
   1. if T wave is greater than 2/3 height of R wave it is abnormal.

RAE

1. P amplitude >2.5 mm in II.
2. Rarely isolated finding (usu rvh/rad too).
3. large diphasic p wave in V1. Right atrial hyper.-initial component is larger in V1 than V6 :tall p wave, bigger than 2.5 boxes in limb leads.
4. p-mitrale-m notched p wave in leads 1 and 2. Greater than .12 seconds.

LAE

1. Biphasic P in V1 w/ wide, deep terminal component, >1mm depth & wide.
2. 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. LVH-s wave in V1 or V2 (biggest) plus R in V5 or V6 (biggest) is greater than 35mm. 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 (all qrs intervals should be measured in limb leads)
2. triphasic QRS (RSR') in ant precord leads (V1-V3), often w/ st dep & twi in these leads
3. assoc w/ org heart dz (cant cause rad on own)

1. QRS greater than .12.
2. slurred s in 1 and V6.
3. RSR' in V1 with R' taller than R.
4. V1 must have a positive complex.

LBBB

1. QRS > 0.12 in limb leads, w/ lg, broad , notched or slurred R waves in lat precord leads (V5-V6) & lead I & avL, the st seg is usu depressed & twi in these leads!
2. can cause lad, ste seen in ant leads but can call ant mi in rbb!

1. duration equals .12sec
2. broad monomorphic R waves in 1 and V6 without Q waves.
3. broad monomorphic S waves in V1, may have a small r wave.

LASH

(caused by CAD, valv. dis., cong. dis., cardiomyop., myocard.)

1. Axis < -45 (L axis) w/QRS <0.10s
2. deep S in II, III, and AVF
3. exclude other cause of L axis (habitus, Inf. MI, hyperK, Vent. pre-excitation)

L Post Inf Hemiblock

(USU. organic heart dis.)

1. R axis (>110) w/ QRS < 0.10s
2. R waves in II, III, AVF.
3. Exclude other causes (COPD, RVH, Lat MI)
4. (-w/ combined blocks cons. pacing only if sxs w/ bradyarrhythmias)

Source

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