Interpolated Extra-Systoles. 



7 



averages about 60. It may go as low as 50 during rest. The 

 extra-systoles average about 35 per minute during rest and 45 

 after vigorous exercise. The ectopic beat follows the normal 

 contraction by a period averaging Yl second. The pause following 

 the extra-systole is variable; occasionally it is fully compensatory. 

 The dominant rhythm is but slightly disturbed, as a rule. Often 

 it is strikingly constant, and it is seldom more variable than the 

 rhythm of many normal hearts. This is remarkable in view of the 

 fact that in the tracings there is good evidence of retrograde 

 contractions of the auricle which beats prematurely in response to 

 the heterogenetic stimulus. Evidence for the retrogression is 

 found in the absence of the "a" wave at certain cycles. In place 

 of the "a" wave there is often seen a wave which precedes the 

 normal auricular systole by 3/30 to 5/30 of a second. This prema- 

 ture wave is also preceded by a wave practically synchronous with 

 the extra-systole of the ventricle. 



The interpretation of the curves has been uncertain because 

 of the unusual character of the phlebograms and cardiograms 

 and because of the difficulty in establishing proper time relations. 

 While several explanations may be offered for the type of irreg- 

 ularity exhibited, the evidence points to the one given as plausible, 

 but not altogether satisfactory. 



Physiologically this heart is interesting because of the following 

 characters : 



1. It very rarely has periods in which its action is absolutely 

 normal. These periods are of short duration. 



2. The normal sinus rate is slow. 



3. Functionally the heart meets all ordinary demands made 

 upon it. 



4. There is a bathmotropic disturbance which causes persistent 

 interpolated extra-systoles. 



5. The number of extra-systoles is not decreased, except 

 slightly in a few tracings, by an increase in the heart rate due to 

 exercise. The tendency is for the number to rise with acceleration 

 of the normal beat. 



6. The pause following the extra-systole is variable. Occa- 

 sionally it is compensatory. 



7. There is strong evidence that the extra-systole of the 



