Heart Education

2° AV Block Type I




These blocks typically arise from the HIS- Purkinje system and therefore pose more of a problem for the patient.
The typical pattern for this type of block, as seen on EKG, is a PR prolongation leading to a dropped beat.
“A type I block manifesting with atypical electrocardiographic findings that result in a misdiagnosis of type II block is not uncommon. During very long sequences (typically >6:5), PR interval prolongation may be minimal until the last beat of the cycle, when it prolongs abruptly, or the AV interval may shorten and then lengthen in the middle of the sequence. Postblock PR interval shortening remains the cornerstone of the diagnosis of type I block, regardless of whether the periodicity has typical or atypical features.” (17)

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