The Wenkebach phenomenon is characterised by the progressive lengthening of the PR interval with successive heart beats, culminating in a non-conducted atrial depolarisation. The next beat has a short PR interval and so the cycle continues.
The level of the block is generally at the level of the atrioventricular node, the QRS complexes are of normal duration and junctional automaticity, in general, is unimpaired.
In patients with myocardial infarction this particular type of heart block is usually benign.
In the healthy individual the Wenkebach phenomenon is often due to increased vagal tone and is abolished by exercise and atropine.
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