abnormal heart right atrium morphology abnormal sinoatrial node morphology MP:0004115 MPheno.ontology abnormal SA node abnormal pacemaker abnormal sinu-atrial node abnormal sinuatrial node abnormal sinus node any structural anomaly of the small mass of modified cardiac muscle fibers located at the junction of the superior vena cava and the right atrium that is the source of contraction impulses for the heart abnormal impulse conducting system morphology