Analysis of variations in cycle length and the mechanism of atrial flutter studied in patients

In a study group of 12 patients with common atrial flutter, atrial electrograms were recorded from an intra-oesophageal lead together with a surface lead (V1). Upon the onset of the QRS complex, atrial flutter intervals increased after a latency of 100-150 ms to maximal values of 450-500 ms after the QRS complex and subsequently decreased to reach minimal values 400-450 ms later. The hypothesis was formulated that these periodic variations in atrial flutter intervals following a ventricular contraction were caused by the influence of stretch of the atrial myocardium on the conduction properties of a circulation impulse in the atrium. This hypothesis was tested in a simulation study which revealed that the alternation in intervals as found in patients could only be reproduced if the excitable gap in the circus movement was partially excitable.