Trigeminal Tachycardia: Alternate Cycle Interpolation
Report:
Sinus rhythm 85/min
VEBs, interpolated in alternate cycles
Trigeminy
Comment:
The P waves are regular throughout, but the PR intervals alternate, due to interpolation of the VEBs. The LBBB pattern of the VEBs has a characteristically slurred downstroke of right ventricular VEBs.
There is an overall tachycardia which is, as it were, 1/3 ventricular in origin! Interpolation in alternate cycles is a relatively common pattern, resulting in trigeminy. This is most lucidly explained by Schamroth40. Just imagine the concealed retrograde conduction, prolonging the post-VEB PR intervals, replaced by complete block for the P waves concerned: this would become a common or garden bigeminy. Trigeminy in alternate cycles is thus bigeminy manqué.
I saw this patient again 20 years later, in 1996; both he and his wife recalled the car accident and the propranolol-induced equanimity when asked, amazed at my memory. Of course, I did not remember them â but I had been using his ECG for teaching ever since!
41. Irritable heart in a 61 year old woman with hæmorrhagic pancreatitis. There was no other evidence of heart disease. The electrolytes were normalised.
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