Glossary | Page 22 of 24 | Executive Electrocardiogram Education

THIRD DEGREE SINOATRIAL (SA) EXIT BLOCK

THIRD DEGREE SINOATRIAL (SA) EXIT BLOCK: A disorder of the sinus node in which no SA nodal action potentials are able to leave the SA node (no P waves seen). Appears as sinus arrest and can actually only be diagnosed with a sinus node electrode during an electrophysiology study.

TORSADES DE POINTES

TORSADES DE POINTES: Polymorphic ventricular tachycardia associated with a prolonged QT interval.

TRANSITION

TRANSITION: A measure of the axis of the heart in the transverse (horizontal) plane (that is, from the view of the precordial or chest leads). •Normal Transition. •QRS complex is isoelectric in lead V3 or V4. See: Early transition; and Late transition.

TRIGEMINY

TRIGEMINY: Abnormal heart beats occurring every third beat (e.g. atrial trigeminy – premature atrial complexes (PACs) occurring every third beat; ventricular trigeminy – premature ventricular complexes (PVCs) occurring every third beat).

TRIPHASIC

TRIPHASIC: The trend of the deflection of an ECG signal to go in three directions (e.g. the signal begins at baseline, goes up [positive], then goes down [negative], then goes up [positive] again, and then back to baseline).

TRIPLET

TRIPLET: Three abnormal beats in a row (e.g. atrial triplet – Three premature atrial complexes in a row; ventricular triplet – Three premature ventricular complexes in a row).

U WAVE

U WAVE: Deflection on the ECG that can occur after the T waves.

UNIPOLAR LEADS

UNIPOLAR LEADS: Leads which use one electrode as a positive pole and Wilson’s Central Terminal (WCT) as the negative pole.

UNIPOLAR PACING

UNIPOLAR PACING: A cardiac pacing system in which the cathode (positive pole of the pacemaker circuit) is at the tip of the pacemaker wire and the anode (negative pole of the pacemaker circuit) is the pacemaker generator.

UPPER RATE TRACKING LIMIT

UPPER RATE TRACKING LIMIT: The fastest ventricular rate that the pacemaker is allowed to pace in response to atrial activity (used in dual chamber pacemakers).