12-LEAD ECG's - A "Web Brain" for Easy Interpretation

Electrolyte Disturbances

Hyperkalemia

An ECG should be obtained when electrolyte disturbance is suspected, especially for hyperkalemia (in which a fairly good correlation does exist between ECG findings and the serum potassium [K+] level).

A
normal

B
shows peaking of the T wave, which is the earliest change (K+ about 6-7 mEq/L)

C
The T wave becomes taller and  more peaked (K+ about 7-8 mEq/L); it almost looks like the Empire State building (tall, peaked, with a narrow base). Contrast with the T wave that is sometimes seen in healthy individuals as a normal variant (shaded box) in which the T wave is rounded, its sides are not symmetric, and it has a broad base.

D
P wave amplitude decreases, the PR interval lengthens, and the QRS widens (K+ >8 mEq/L).

E
P waves disappear (sino- ventricular rhythm) and the QRS becomes sinusoid (K+ >10 mEq/L). V Fib usually follows.

Hypokalemia

Although the ECG is a fairly good indicator of hyperkalemia, it is not reliable for detecting hypokalemia.  However, when ECG changes are seen they tend to be those that are shown in this figure.

A
normal

B
shows flattening of the T wave, which is the earliest change

C and D
A "U wave" then develops, associated with ST-T wave flattening and sometimes slight ST depression. A "pseudo P-pulmonale" pattern may be seen.

E and F
ST depression is more  noticeable and the U wave increases in amplitude until ultimately the U wave overtakes the T wave.  At this point distinguishing between the T wave and U wave may be almost impossible ("Q-U" prolongation).

Note - The ECG changes of hypomagnesemia are identical to those of hypokalemia. Hypomagnesemia is often seen in association with other electrolyte abnormalities (low sodium, potassium, calcium, or phosphorus); acute MI; cardiac arrest; digoxin or diuretic therapy; alcohol abuse, renal impairment.

	12-LEAD ECG's - A "Web Brain" for Easy Interpretation