Wagner_Marriot's Practical Electrocardiography, 12e

I

II

III

A

I

II

III

B F I G U R E 2 2 . 4 .

Leads I, II, and III rhythm strips from a patient with chronic pulmonary disease and receiving digitalis therapy (A) and a woman with hypertension and receiving both -adrenergic and calcium antagonist therapy (B) . Arrows indicate failure of AV conduction and therefore the pres- ence of second-degree AV block.

A second-degree AV block may be intermittent (Fig. 22.4A) or continuous (see Fig. 22.4B). Note that in Figure 22.4A, the second-degree block occurs only after a sequence of six con- ducted beats, of which the first shows no AV block and the latter five show first-degree block (7:6 block). In Figure 22.4B, there is continually alternating first- and second-degree AV block with a 2:1 AV ratio. This is termed 2:1 (AV) block.

459

CHAPTER 22: Atrioventricular Block