ECG Basics
General
1 small box = 1mm = 0.04 sec = 40 mili-seconds
5 small boxes = 1 big box = 5mm = 0.2 sec = 200 mili-seconds
- varries with HR
Intervals
ECG Seconds mm (sm boxes)
P 0.10 2.5
PR 0.12-0.20 3-5
QRS 0.06-0.10 1.5-2.5
Q <0.04 1
- QT 0.33-0.42 8.25-10.5
QTc <0.44 NA
Axis
axis and ventricular hypertrophy
cannot be measured correctly in presence of BBBs....
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.
posterior hemiblock-right axis deviation and S1Q3.
Axis-check lead 1 and AVF..If both are positive then axis is normal .
Find isoelectric lead. Axis is perpendicular.
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
-sig Q waves are @ least 1 mm (1 box) wide or @ least 1/3 of the entire QRS amplitude.
Early Repolarization:
-STE most prominent in lat precord leads (V4-6) but no reciprocal chngs. T waves here usu broad, tall (usu > 5mm) & upright.
-limb leads may also have ste, rarely >2 mm
T waves
T waves are normally upright in 1,2,V3 to V6. Negative in AVR.
-if T wave is greater than 2/3 height of R wave it is abnormal.
RAE
-P amplitude >2.5 mm in II.
-Rarely isolated finding (usu rvh/rad too).
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.
p-mitrale-m notched p wave in leads 1 and 2. Greater than .12 seconds.
LAE
-Biphasic P in V1 w/ wide, deep terminal component, >1mm depth & wide.
Left atrial hyper.-terminal component is larger than .04 sec.
LVH
-Sum of S in V1 or V2 & R in V5 or V6 is >35mm.
-Sum of highest R & deepest S in precord is >45mm
-R wave in V6 > 18mm
-R in AVL of >12mm
-L precordial leads may show ST depression & twi= LV strain pattern
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
-Dominant R in V1 >7mm (also seen in WPW, RBBB, post MI, & nml var.)
-RSR in V1 w/ QRS < 0.12
-This dx usu also w/ RAE or strain (ST dep w/ twi in V1-V3).
-Less sens. & spec. than LVH, usu nl ecg
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.
(note: R :S ratio greater than 1 also in: 1.RBBB 2.WPW type A. 3. Post. Wall MI. 4.kids.)
RBBB
-QRS > 0.12 in limb leads (all qrs intervals should be measured in limb leads)
-triphasic QRS (RSR') in ant precord leads (V1-V3), often w/ st dep & twi in these leads
-assoc w/ org heart dz (cant cause rad on own)
RBBB-
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.
LBB
-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!
-can cause lad, ste seen in ant leads but can call ant mi in rbb!
LBBB-
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.)
-Axis < -45 (L axis) w/QRS <0.10s
-deep S in II, III, and AVF
-exclude other cause of L axis (habitus, Inf. MI, hyperK, Vent. pre-excitation)
L Post Inf Hemiblock
(USU. organic heart dis.)
-R axis (>110) w/ QRS < 0.10s
-R waves in II, III, AVF.
-Exclude other causes (COPD, RVH, Lat MI)
(-w/ combined blocks cons. pacing only if sxs w/ bradyarrhythmias)
Source
9/09 DONALDSON (adapted from Niemann, Lampe, Pani)