The location of atrioventricular (AV) block can sometimes be determined using an algorithm with a series of steps.
Step 1: QRS duration
(1a) prolonged (>= 0.12 seconds): proceed to step 2
(1b) normal (< 0.12 seconds): block in AV node
Step 2: presence of conducted beats
(2a) present: proceed to step 3
(2b) none present: location not indicated
Step 3: variation in PR interval (conduction time)
(3a) no variation (constant PR interval): proceed to step 4
(3b) variation (Type I): block in AV node
(4a) variable RP intervals (Type II): block in bundle branches
(4b) constant RR intervals: location not indicated
• The RP interval is the time between a conducted QRS complex and the next conducted P wave.
Exception: AV block may rarely arise in the common bundle. Consider if: normal QRS interval + variable RP intervals (Type II).
Failure to Localize
If the location of the block cannot be identified, then the patient should be managed as if the block were located in the bundle branches since this has more serious clinical consequences.
(1) A temporary pacemaker should be inserted.
(2) His bundle electrograms with an intracardiac recording should be performed.
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