The QRS complex on an ECG represents ventricular depolarization, with wide or narrow complexes indicating various heart conditions. It is useful in diagnosing arrhythmias, ventricular hypertrophy, myocardial infarction, and electrolyte imbalances. Some supraventricular tachycardias may require treatment.
The QRS complex is a specific sequence of deviations seen on a printout of an ECG, representing depolarization of the right and left ventricles of the heart. An ECG printout shows five deflections, or waves, arbitrarily labeled 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 large downward deflections. the top, or tip. The S wave is the small downward deflection that follows the R wave.
The time intervals between the QRS complex determine the ventricular rate. A normal one lasts 80 to 120 milliseconds. Wide QRS complexes, or those that last longer than normal, indicate impairment of the ventricle such as bundle branch blocks. Often with bundle branch blocks, a second upward deflection occurs within the complex. Other causes of a large QRS complex include ectopic foci or abnormal pacemaker sites that slow conduction within the heart and increase the time for the heart muscle to depolarize.
Narrow QRS complexes are often observed in children and patients with tachycardia. These indicate an arrhythmia in or above the AV 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 ailments. Cardiac arrhythmias, ventricular hypertrophy, myocardial infarction, conduction abnormalities, and electrolyte imbalances can be diagnosed by analyzing the QRS complex on an ECG.
Most supraventricular tachycardias (SVT) are not life-threatening. Some SVTs indicated by wide or narrow QRS complexes, however, may require treatment. Physical maneuvers that activate the parasympathetic nervous system, also called vagal maneuvers, increase intrathoracic pressure and affect the pressure sensors within the arch of the aorta.
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