Wagner_Marriot's Practical Electrocardiography, 12e

Step 1

QRS duration normal

QRS duration prolonged

Block in AV node

Step 2

No conducted beats present

Conducted beats present

Location not indicated

Step 3

Variation in conduction time (PR interval) (Type I)

No variation in conduction time (PR interval)

Block in AV node

F I G U R E 2 2 . 1 8 . The four-step algorithm for iden- tifying the location of AV block from an ECG recording. Step 1: Consider the duration of the QRS complex. Step 2: Consider whether conducted beats are present. Step 3: Consider whether there is variation in the conduc- tion times. Step 4: Consider whether there are constant PR intervals with changing RP intervals. Situations that indicate an end point in the algorithm are indicated by boxes with accentuated borders .

Step 4

Constant PR intervals only occuring with constant RR intervals

Constant PR intervals with variable RP

intervals (Type II)

Location not indicated

Block in bundle branches

A stepwise method for determining the location of AV block is illustrated in Figure 22.18. This algorithm does not consider the localization of AV block within the common bundle because of the rarity of AV block in this location. (Such a location should be considered only when a QRS complex of normal duration [step 1] is accompanied by a pattern char- acteristic of type II block [step 4].) Note that both steps 2 and 4 may lead to situations in which it is impossible to determine the location of a block from a particular ECG record- ing. In this case, additional recordings should be obtained. If these are also nondiagnostic, the patient should be managed as though the block were located in the bundle branches because such a location has the most serious clinical consequences. This usually requires insertion of a temporary pacemaker, which provides time for further studies to determine the location of the AV block. His-bundle electrograms can be obtained via intracardiac re- cordings. A prolonged atrial-to-His interval (from the onset of the atrial signal to the time of the His-bundle signal), or the absence of a signal from the His bundle, indicates block in an AV nodal location, whereas a prolonged His-to-ventricle interval (from the His-bundle signal to the onset of the ventricular signal), or absence of a signal from the ventricles after a His signal, indicates block in a bilateral bundle branch location (see Fig. 14.11).

473

CHAPTER 22: Atrioventricular Block