The ornamental design for an electrocardiograph, as shown and described.
FIG. 1 is a perspective view of an electrocardiograph, showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a bottom view thereof; and,
FIG. 8 is an enlarged view of the encircled portion 8 as shown in FIG. 1.
The short dash-dash broken line in the figures represents unclaimed portions of the electrocardiograph and the dot-dot-dash broken line in FIGS. 1 and 8 encircling a portion of the claimed design are for illustrating the enlargement; the broken lines form no part of the claimed design.