Defining the QRS Complex

 

 

 

 

 

 

The Wave Form

P wave- the arch preceding the QRS complex.

Q wave- the first negative (downward) deflection of the complex. In some leads, it will not be present. In some cases, the complex begins with an R wave.

R wave- the first positive (upward) deflection of the QRS complex. It will sometimes be preceded by a Q wave.

S wave- any negative (downward) deflection following an R wave.

T wave- the arch following the QRS complex.

 

The Electrical and Mechanical Equivalents

P wave- this represents atrial depolarization. It is followed by an isoelectric segment, which is due to a conduction delay at the AV node.

QRS- the complex represents the depolarization of the ventricles. This is followed by an isoelectric segment.

T wave- this represents ventricular repolarization.

Atrial Contraction- the atria mechanically contract starting at the beginning of the P wave, until the beginning of the QRS complex.

Ventricular Contraction- the ventricles mechanically contract from the start of the QRS complex until the end of the T wave.

The EKG Paper

The EKG paper is divided into large boxes, which are further divided into smaller boxes. Each large box is demarcated by thick black lines. Within the borders of one large box lie five smaller boxes. On the horizontal axis, one large box represents 0.2 seconds (see figure directly above). On the horizontal axis, each small box represents 0.04 seconds. On the vertical axis, each small box represents 1 millimeter.

References:

Dubin D. Rapid Interpretation of EKG’s. 6 th Ed. Tampa: Cover Publishing, 2000.

Grauer K. 12-Lead ECG’s: A “Pocket Brain” for Easy Interpretation. 2 nd Ed. Gainesville: KG/EKG Press, 2001.

Lilly LS. Pathophysiology of Heart Disease: a Collaborative Project of Medical Students and Faculty. 3 rd Ed. Baltimore: Lippincott Williams & Wilkins, 2003.

Podrid PJ. ECG tutorial: Approach to Interpretation. www.uptodate.com, 2005.