Ecg: Reading The Waves

ECG: Reading the Waves An electrocardiogram (ECG), seen on the right, represents movement of electrical current (depicted in green) through the heart during a heartbeat. The first wave of the ECG, designated P, represents initiation of the heartbeat in the upper chambers of the heart (atria); the QRS complex represents movement of the electrical current through the lower chambers of the heart (ventricles); and the T wave represents the recovery phase, in which the electrical current spreads back over the ventricles in the opposite direction. The heart, seen on the left, is beating in time with the ECG. Oxygen-depleted (blue) blood is pumped from the heart to the lungs, which supply oxygen; oxygen-enriched (red) blood returns from the lungs to the heart and is pumped throughout the body.

ECG Waves and Intervals

P

wave: the sequential activation (depolarization) of the right and left atria

QRS complex: right and left ventricular depolarization (normally the ventricles are activated simultaneously) ST-T wave: ventricular re polarization U wave: origin for this wave is not clear - but probably represents "after depolarizations" in the ventricles PR interval: time interval from onset of atrial depolarization (P wave) to onset of ventricular depolarization (QRS complex)

QRS duration: duration of ventricular muscle depolarization QT interval: duration of ventricular depolarization and repolarization RR interval: duration of ventricular cardiac cycle (an indicator of ventricular rate) PP interval: duration of atrial cycle (an indicator or atrial rate)

Conduction Analysis "Normal"

conduction implies normal sino-atrial (SA), atrio-ventricular (AV), and intraventricular (IV) conduction.

The following conduction abnormalities are to be identified if present:

• SA block: 2nd degree (type I vs. type II) • AV block:1st, 2nd (type I vs. type II), and 3rd degree • IV blocks: bundle branch, fascicular, and nonspecific blocks • Exit blocks: blocks just distal to ectopic pacemaker site

Wave form Description Carefully analyze the 12-lead ECG for abnormalities in each of the waveforms in the order in which they appear: P-waves, QRS complexes, ST segments, T waves, and... Don't forget the U waves. • P waves: are they too wide, too tall, look funny (i.e., are they ectopic), etc.? • QRS complexes: look for pathologic Q waves, abnormal voltage, etc. • ST segments: look for abnormal ST elevation and/or depression. • T waves: look for abnormally inverted T waves. • U waves: look for prominent or inverted U waves.