What is the QRS Complex?

Maria Overstreet

The QRS complex is a specific sequence of deflections seen on the printout of an ECG, representing the depolarization of the right and left ventricles of the heart. An ECG printout shows five deflections, or waves, that are arbitrarily named P, Q, R, S and T. Q waves are displayed as small downward deflections following the P wave, and the R wave is shown as a large upward deflection, or spike. The S wave is the small downward deflection following the R wave.

Narrow QRS complexes are often seen in patients with tachycardia.
Narrow QRS complexes are often seen in patients with tachycardia.

The time intervals between the QRS complex determine the ventricular rate. A normal one lasts 80 to 120 milliseconds. Wide QRS complexes, or those lasting longer than the normal rate, indicate ventricle impairment such as bundle branch blocks. Often with bundle branch blocks, a second upward deflection occurs within the complex. Other causes for a wide QRS complex include ectopic foci or abnormal pacemaker sites that slow conduction within the heart and increase the time for depolarization of the heart muscle.

Tachycardia is defined as having a heart rate that exceeds 100 beats per minute.
Tachycardia is defined as having a heart rate that exceeds 100 beats per minute.

Narrow QRS complexes are often seen in children and in patients with tachycardia. These indicate an arrhythmia within or above the atrioventricular node. Sinus tachycardia, atrial fibrillation, atrial flutter, and supraventricular tachycardia cause this condition. Cardiologists and other medical professionals find the QRS complex useful in diagnosing a variety of disorders. Cardiac arrhythmias, ventricular hypertrophy, myocardial infarction, conduction abnormalities and electrolyte imbalances can all be diagnosed by analyzing the QRS complex on an ECG.

The QRS complex is a specific sequence of deflections seen on the printout of an ECG, representing the depolarization of the right and left ventricles of the heart.
The QRS complex is a specific sequence of deflections seen on the printout of an ECG, representing the depolarization of the right and left ventricles of the heart.

Most supraventricular tachycardia (SVT) are not life-threatening. Some SVT indicated by wide or narrow QRS complexes, however, might require treatment. Physical maneuvers activating the parasympathetic nervous system, also called vagal maneuvers, increase intrathoracic pressure and affect the pressure sensors within the aorta’s arch.

Cardiac arrhythmias can be diagnosed by analyzing the QRS complex on an ECG.
Cardiac arrhythmias can be diagnosed by analyzing the QRS complex on an ECG.
Nausea may occur as a result of atrial flutter.
Nausea may occur as a result of atrial flutter.
High blood pressure may cause left ventricular hypertrophy, which can be diagnosed by analyzing the QRS complex on an ECG.
High blood pressure may cause left ventricular hypertrophy, which can be diagnosed by analyzing the QRS complex on an ECG.
An EKG is often used to continuously monitor the heart rate and rhythm of a critically ill patient in order to catch abnormalities quickly.
An EKG is often used to continuously monitor the heart rate and rhythm of a critically ill patient in order to catch abnormalities quickly.
An ECG printout shows five deflections or waves.
An ECG printout shows five deflections or waves.

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