P loops during common and uncommon atrial flutter in man.

Atrial flutter has never been satisfactorily defined. The 'common' pattern of flutter was originally described by Lewis in 1913. Less frequently observed forms of flutter are termed 'uncommon'. Sixteen cases of the 'common' and 6 of the 'uncommon' type have been studied using isolated P loop vectorcardiography. All patients had some degree of atrioventricular block but none had evidence of digitalis excess. The atrial rates were regular and were in a range between 250 and 330/minute. Vagal manoeuvres increased AV block in each instance. All those with the 'common' type of flutter had P loops with a caudad-cephalad orientation and fifteen of the sixteen had forces which descended over the right atrium and ascended over the left atrium. The 6 cases of the uncommon type of flutter had rates which ranged between 250 and 300/minute and did not fulfil both of the criteria for 'common' flutter; namely continuous baselineu ndulation and prominent negative P deflections in the inferior leads. The cases with the 'uncommon' type of flutter had a variety of loop patterns. The most frequent type was oriented inferior slightly to the right and anterior. One patient satisfied criteria for left atrial flutter. In another the loop was oriented inferior leftward and anterior. The vectorcardiogram provides a rich source of descriptive data but does not identify the underlying mechanism(s) of flutter.