CLINICAL APPLICATIONS OF ELECTROCARDIOGRAPHS 281 



levocardiogram are seen (Figs. 87 and 88). Any one or several of the general 

 types of extrasystole may occur in the same patient. Fig. 88 shows 

 an extrasystole originating from the left ventricle. 



Paroxysmal Tachycardia. Electrocardiographic records taken in the 

 interval between the paroxysms may appear normal. During the tachy- 

 cardia the records normally show only two deflections, R and a combina- 

 tion of T and the succeeding P (Fig. 89). If the paroxysm is of auric- 

 ular origin, the P deflection may be inverted, indicating that the new 

 focus of impulse production is located at some other site than the sino- 

 auricular node. 



Auricular Fibrillation. The electrocardiogram in auricular fibrilla- 

 tion shows three distinctive features: 

 l^. Absence of the P deflections typical of auricular contractions. 



2. The ventricular complexes (Q-R-S-T waves) occur in irregular se- 

 /quence and may vary in height. 



3. The presence of small irregular oscillations best seen, between the 

 ventricular complexes. A typical tracing of this condition is shown in 

 Fig. 90. 



The dependence of the P-wave upon auricular contraction has been 

 indicated (page 272). Its absence in auricular fibrillation is accounted 

 for by the fact that the individual muscle fibers of the auricles contract 

 independently of one another, so that some fibers are in a state of con- 

 traction while others are relaxed. This renders impossible a coordinate 

 contraction of the auricle as a whole. 



The multiple impulses from the fibrillating auricles reach the ventri- 

 cles and evoke a contraction provided the ventricle is not already in a 

 state of contraction (refractory period, page 178). These irregular 

 ventricular responses will of course produce unequal spacing of the 

 ventricular complexes in the electrocardiogram. The variations in the 

 height of the R deflections is thought to be due to the distortion caused 

 by the superimposition of the small waves representing auricular ac- 

 tivity. 



Auricular Flutter. Auricular flutter was discovered by the electro- 

 cardiograph, and it is practically impossible to make a diagnosis of this 

 condition without the use of the string galvanometer. The auricular 

 deflections are usually rhythmic and in the average case vary in rate 

 from 20QJ&J350 per minute. The initial deflection of P may be di- 

 rected either upwards or downwards, depending on the site of the 

 origin of the auricular impulse (when arising from some other source 

 than the S-A node the impulse is said to be ectopic). Usually a regular 

 succession of P deflections can be traced throughout the record (Fig. 91). 



