Be systematic and always compare to old EKG:
- Rate, rhythm.
- Machine rate usually accurate. Caution: tall t waves in hyperkalemia, and tall p waves (e.g., bad COPD) can be read by computer as QRS complexes.
- Look at rhythm strip to eval for arrhythmias.
- Intervals, axis.
- Chamber size.
- p waves for atrial abnormalities.
- QRS for LVH.
- Ischemia: see ACS sections.
Rhythm
- Sinus rhythm: normal p wave before each QRS. Normal p wave axis (upright in I, II, aVF, down in aVR).
- Supraventricular tachycardia or narrow complex tachycardia:
- Regular: sinus tachycardia, atrial tachycardia, AVNRT, AVRT, junctional tachycardia, atrial flutter).
- Irregular: atrial fibrillation, MAT (multifocal atrial tachycardia), atrial flutter with variable conduction (atrial rate >240 and usually ~300).
- Wide complex tachycardia (VT, SVT with LBBB): see section Diagnosis of Wide-Complex Tachycardia.
- Polymorphic VT or Torsades de Pointes.
- Ventricular fibrillation.
Differential Diagnosis of Axis Deviations (in order of likelihood).
Right Axis |
Left Axis |
---|---|
1. RVH or Strain |
1. Left anterior fascicular block |
2. Lateral or anterolateral MI |
2. Inferior MI |
3. WPW with left freewall pathway |
3. WPW with posteroseptal pathway |
4. Left posterior fascicular block |
4. LVH |
Right atrial abnormality (only 1 criteria needed)
lead II P > 0.25 mV or > 25% QRS amplitude
lead V1 P > 0.15 mV
Left atrial abnormality (only 1 criteria needed)
lead II P > 120 msec with notches separated by at least 1 small box
lead V1 P wave has a negative terminal deflection that is 40 msec by 0.1 mV
Left ventricular hypertrophy
There are numerous criteria; three useful ones below. All are specific but all are insensitive, so fulfillment of one set is sufficient for LVH (applies to > 35 y.o.)
R in aVL >11 mm (men), >9 mm (women)
Rin aVL + S in V3 >20 mm (women) and >25 mm (men)
Sin V1 + (R in V5 or R in V6) >35 mm
Right ventricular hypertrophy
The following findings suggest RVH; there are several others.
Right axis deviation
R in V1 + S in V6 > 11 mm
R:S ratio > 1 in V1 (in absence of RBBB or posterior MI)
RBBB (Right Bundle Branch Block)
QRS > 120 msec
Wide S wave in I, V5, V6
Secondary R wave (R’) in right precordial leads with R’ greater than initial R (rsR’ or rSR’).
LBBB (Left Bundle Branch Block)
QRS > 120 msec, broad R in I and V6, broad S in V1 and normal axis or
QRS > 120 msec, broad R wave in I, broad S in V1, RS in V6, and left axis deviation.
LAFB(Left Anterior Fascicular Block)
There are several sets of criteria for LAFB
Axis is more negative than –45 degrees
Q in aVL, and time from onset of QRS to peak of R wave is >0.05 s.
Also helpful is QI, SIII pattern
LPFB (Left Posterior Fascicular Block; must rule out anterolateral MI, RVH, RBBB)
Axis >100 and QIII, SI pattern
Q Waves
Use the following screening mantra, courtesy of Tom Evans, M.D. V1, V2, V3: "any, any, any"; V4, V5, V6: "20, 30, 30"; I, II, aVL, aVF: "30, 30, 30, 30"; V1, V2: "R > 40, R > 50". Numbers refer to width of Q wave in milliseconds.