Heart block is a condition in which the electrical impulses that coordinate the heartbeat are delayed or completely blocked as they travel from the atria to the ventricles. It is classified into first degree, where conduction is slowed; second degree, where some beats are blocked; and third degree, or complete heart block, where no impulses reach the ventricles and they beat independently. On echocardiography, heart block affects the timing relationship between atrial and ventricular contractions visible on M-mode and Doppler tracings. In fetal ultrasound, complete heart block presents as a persistently slow fetal heart rate and can be evaluated by simultaneously recording atrial and ventricular wall motion with M-mode.
Sonography Term