QRS complex

The QRS complex is the combination of three of the graphical deflections seen on a typical electrocardiogram (ECG or EKG).

It corresponds to the depolarization of the right and left ventricles of the heart and contraction of the large ventricular muscles.

The Q, R, and S waves occur in rapid succession, do not all appear in all leads, and reflect a single event and thus are usually considered together.

The duration, amplitude, and morphology of the QRS complex are useful in diagnosing cardiac arrhythmias, conduction abnormalities, ventricular hypertrophy, myocardial infarction, electrolyte derangements, and other disease states.

High frequency analysis of the QRS complex may be useful for detection of coronary artery disease during an exercise stress test.

[2] Duration longer than 45 ms might indicate left posterior fascicular block, LVH or LBBB.

Pathologic Q waves occur when the electrical signal passes through stunned or scarred heart muscle; as such, they are usually markers of previous myocardial infarctions, with subsequent fibrosis.

The J-point is easy to identify when the ST segment is horizontal and forms a sharp angle with the last part of the QRS complex.

However, when the ST segment is sloped or the QRS complex is wide, the two features do not form a sharp angle and the location of the J-point is less clear.

If both complexes were labeled RS, it would be impossible to appreciate this distinction without viewing the actual ECG.

[25] In recent research, heart beat detection methods based on visibility graphs have been introduced, enabling fast and sample-precise R-peak annotation even in noisy ECG.