460
SECTION III: Abnormal Rhythms
Second-degree AV block may have any ratio of P waves to QRS complexes (Fig. 22.5).
In Figure 22.5A, there are the commonly appearing 3:2 and 4:3 AV conduction ratios.
However, in Figure 22.5B the sinus rate is in the tachycardia range, and the more rapid
“bombardment” of the AV node causes the 2:1 ratio to be intermittently increased to 3:1.
I
II
III
A
I
II
III
B
F I G U R E 2 2 . 5 .
Leads I, II, and III rhythm strips from a patient with chronic bronchitis and
cor pulmonale
(A)
and a 79-year-old woman with acute pulmonary edema
(B)
, both of whom were
receiving long-term digitalis therapy for heart failure.
Arrows
indicate P waves that completely fail
to conduct to the ventricles.
