Severe hyperpotassemia is a rare cause of complete AV block, although PR prolongation is fairly common. When high grade or complete block complete does occur, the rate of the escape pacemaker is usually very slow. This represents an acute medical emergency since any further increase in the serum potassium concentration will likely result in asystole.
This tracing is from a 73 year old male with a prior myocardial infarction hypertension and chronic renal insufficiency. His presenting complaint was dizziness. P waves (arrows) are difficult to appreciate because they are broad and of low amplitude. Their rate is 83 (PP interval = 0.72 seconds). There is complete AV block with AV dissociation and a wide complex escape rhythm with a rate of 26 (the RR interval is 2.3 seconds). The QRS complex is diffusely widened with a duration of 0.18 seconds. At the time of this tracing, the serum potassium level was 8.6 mm/l.