Latent Heart Block.

I have used the term "Latent Heart Block" to indicate a prolonged P-R interval without any manifest degree of block, such as dropped beats or 2 :1 block. This paper is a clinical study of a series of such cases, mainly from the point of view of the xtiology and significance of the condition. One might guess that latent heart block would be found in the same cases as, but at an earlier stage than, higher grades of heart block; and that a patient would progress from latent to dropped beats, next to 2: 1, and finally to complete heart block. But such a regular sequence is not common. Shortly, one can say that latent heart block is found in any type of heart disease at any age without much tendency to progress, and that there is a complete contrast with the wellrecognized xtiology of complete heart block, which is atherosclerosis and high blood pressure in elderly patients. As might perhaps be expected, latent block is more often transient than is the case with complete block, but it is often persistent at a fairly steady level for long periods. It is also seen-sometimes to an unusual degree-in hearts that appear to be normal otherwise; here it may be an extreme instance of vagal activity (Fig. 1). ........__........... ...,,= .. ...... .. titrA__________ __ iiiii~~~~~.... PO