Atrial flutter with inapparent flutter waves on the surface electrocardiogram.

A case with inapparent flutter waves on surface electrocardiogram are described. Typical atrial flutter activity could be seen on right atrial monophasic action potential recordings, His bundle electrograms and echocardiograms. During long pauses induced by carotid sinus massage the atrial activity on endocavitary tracings and echocardiograms was unchanged while isoelectric lines were recorded on the twelve surface electrocardiographic leads.