Electrocardiogram 



Since the electrocardiogram is easily obtainable and 

 serves as an important diagnostic tool, considerable 

 efforts have been made by theoretical and clinical 

 scientists to correlate timewise electrical and mechani- 

 cal events of cardiac contraction. Nearly half the 

 large volume of the Physiology of the Heart, by Schiitz 

 (144), is devoted to this subject and should be referred 

 to for detailed information. 



From the standpoint of cardiac pumping, the 

 electrocardiogram is principally of interest insofar as 

 it may furnish a convenient method of determining 

 precisely the course of mechanical events without 

 resorting to surgical interventions, cannulations, etc. 

 Present attempts along these lines are still inadequate. 

 They are also theoretically limited for the following 

 reasons: a) although the electrical event always 

 precedes the mechanical event, it is not known 

 whether the time intervals between depolarization 

 and beginning of contraction are identical in all 

 heart muscle fibers, b) There may be differences in 

 the rates of impulse propagation along various fibers 

 resulting in varying rates of contraction once de- 

 polarization has started at one point, c) As repeatedly 

 emphasized by Rushmer (139) and Scher (142), 

 there is considerable mechanical asynchronicity in 

 the contraction of cardiac muscle fibers, which cannot 

 be completely unraveled by recording the over-all 

 electrical changes from a large mass of tissues such as 

 the heart, d) There are possibly time differences 

 between the right and left heart depolarizations and 

 contractions, but these differences are inconstant 

 and change with various factors. 



An example of the difficulties encountered in 

 attempting to establish empirical time correlations in 

 the cardiac cycle is shown in figure 18. Using normal 

 anesthetized dogs, Gribbe et al. (57) studied the 

 volume changes in the cardiac chambers with 

 cineradiography and timed the events with the 

 conventional electrocardiogram. Comparison of the 

 time relations in figure 19 with those shown in 

 figures 14 and 18 reveals considerable discrepancies. 



Vibrocardiogram (Apex Cardiogram) 



The intracardiac pressures are not easier to corre- 

 late with the electrocardiogram than with a number 

 of other mechanical events [e.g., Harrison et al. 

 (65)]. For instance, the classical mechanocardio- 

 gram or apex cardiogram, now often referred to as 

 precordial vibrocardiogram, offers a good example of 

 the present limitations in the description of the 



FUNCTIONAL ANATOMY OF CARDIAC PUMPING 777 

 I 2 3 4 5 



RIGHT 



-v 



LEFT 



.,...,..,.,. .. ... 1 ,, j.. 



■ I I I II ! I I I 



10 



+4- 



fig. 18. Schematic presentation of the relationship between 

 electrical and mechanical events. Heart rate 120 beats/min. 

 The markings in lower part of the figure indicate the picture 

 frequency at an exposure rate of 48 frames/sec. 1 , Onset of 

 right atrial contraction; 2, onset of right ventricular contrac- 

 tion; 3, onset of right ventricular ejection; 4, end of right 

 ventricular ejection; 5, onset of right ventricular filling; 6, 

 onset of left atrial contraction, 7, onset of left ventricular con- 

 traction; 8, onset of left ventricular ejection; g, end of left 

 ventricular ejection; 10, onset of left ventricular filling. The 

 striped areas represent the phase of ventricular isovolumetric 

 contraction. The stippled areas represent the phase of ventricu- 

 lar ejection. [From Gribbe el al. (57).] 



cardiac cycle. Figure 1 9 shows a composite chart made 

 up of superimposed schematized tracings as they are 

 observed in normal man. The chart has been con- 

 structed by Agress et al. (2) from the most appropriate 

 tracings which they could find in the recent literature. 

 The authors state: "Although this is a composite 

 graph, an accuracy of 0.005 second per scale division 

 was made possible by using a simultaneouslv in- 

 scribed electrocardiogram as the time base." It is 

 evident that claims for an accuracy of 5 msec can be 

 only referred to the electrocardiogram, since the 

 time definition of intracardiac pressure recording 

 through long catheters is usually poorer than 0.005 

 sec. This fact is not pointed out in criticism of the 

 well-deserving attempts to correlate the various 

 events of the cardiac cycle in man, but only for the 

 purpose of cautioning against hasty conclusions. 



Agress et al. (2) divide the cardiac cycle into 

 phases, which differ slightly from those customarily 

 accepted in the past. The curves (fig. 19) are inter- 

 sected by vertical lines based on the time relation of 

 left atrial and left ventricular pressures, as indicated 

 by the upper margin band, /., of the graph and the 

 small heart schemes above it. The phases are labeled 



