Trystan Casey
The Q wave is a component of the QRS complex, which is the combination of three graphical deflections seen on a typical electrocardiogram (ECG). The Q wave is a small negative deflection that precedes the R wave, which is an upward deflection. The Q wave represents the rapid depolarization of the thin septal wall between the two ventricles, and it is referred to as a septal Q wave. In normal circumstances, the Q wave should be no larger than 25% of the associated R wave, and its presence can indicate the loss of positive electrical voltages due to localized necrosis of heart muscle, often associated with myocardial infarction.
| Characteristics | Values |
|---|---|
| Definition | Initial negative deflection of the QRS complex in an electrocardiogram |
| Indication | Loss of positive electrical voltages due to localized necrosis of heart muscle |
| Occurrence | Within the first day following myocardial infarction |
| Pathological Q waves | Consequence of myocardial infarction; wider and deeper than normal Q waves |
| Normal Q waves | Represent depolarization of the thin septal wall between the two ventricles |
| R wave | First upward deflection in the QRS complex |
| R wave progression | Increase in amplitude and duration from leads V1 through V4 |
| Loss of normal R wave progression | Indicative of loss of left ventricular muscle mass |
| S wave | Downward deflection that follows the R wave; reflects ventricular mass |
| QRS complex | Represents ventricular depolarization; normal duration of 0.07 to 0.10 seconds |
| Wide QRS | Indicates abnormal conduction within the ventricles or ventricular origin of an impulse |
| QRS amplitude | Wide normal limits ranging from 5mm to 30mm |
| Causes of large QRS amplitude | Physical fitness and ventricular hypertrophy |
| Causes of low QRS amplitude | Chronic obstructive pulmonary disease, hypothyroidism, and cardiac tamponade |
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What You'll Learn
Q waves are the initial negative deflection of the QRS complex
The Q wave is defined as the initial negative deflection of the QRS complex in an electrocardiogram. The QRS complex is the combination of three of the graphical deflections seen on a typical electrocardiogram (ECG or EKG). It is usually the most visually obvious part of the tracing. The Q wave is a small negative deflection that precedes the R wave.
The QRS complex corresponds to the depolarization of the right and left ventricles of the heart and the contraction of the large ventricular muscles. The ventricular septum receives Purkinje fibres from the left bundle branch, and therefore depolarization proceeds from its left side towards its right side. The vector is directed forward and to the right. The ventricular septum is relatively small, which is why V1 displays a small positive wave (the R-wave) and V5 displays a small negative wave (the Q-wave). Thus, it is the same electrical vector that results in an R-wave in V1 and a Q-wave in V5.
The Q wave results from the depolarization of the interventricular septum, which under normal circumstances occurs from the left ventricle to the right ventricle. Generally, the Q wave should be no larger than 25% of the associated R wave. Normal Q waves, when present, represent depolarization of the interventricular septum. For this reason, they are referred to as septal Q waves and can be seen in the lateral leads I, aVL, V5 and V6.
Pathological Q waves, often a consequence of myocardial infarction, are generally wider and deeper than normal Q waves. Following myocardial infarction with significant loss of myocardium, electrically inactive tissue fails to produce an R wave in the overlying leads; depolarization of the opposite wall in the opposite direction then gets recorded negatively (Q wave). A QR wave denotes a Q wave followed by a substantial R wave.
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They indicate loss of positive electrical voltages
Q waves are defined as the initial negative deflection of the QRS complex in an electrocardiogram. They indicate a loss of positive electrical voltages due to localized necrosis of the heart muscle, which is often associated with myocardial infarction. This infarction can be thought of as an electrical 'hole' as the scar tissue is electrically dead, resulting in pathologic Q waves.
The QRS complex is the combination of three of the graphical deflections observed on a typical electrocardiogram. It is usually the central and most visually obvious part of the tracing. The Q, R, and S waves occur in rapid succession, reflecting a single event, and are thus considered together. The Q wave is any downward deflection immediately following the P wave, while the R wave follows as an upward deflection, and the S wave is any downward deflection after the R wave.
The Q wave results from the depolarization of the interventricular septum, which under normal circumstances occurs from the left ventricle to the right ventricle. Generally, the Q wave should be no larger than 25% of the associated R wave. A normal Q wave may be found in most leads and is a sign of the rapid depolarization of the thin septal wall between the two ventricles. This initial negative deflection of the QRS complex is of short duration and low amplitude.
Pathological Q waves, on the other hand, are often a consequence of myocardial infarction (MI). They are generally wider and deeper than normal Q waves. Following an MI with significant myocardium loss, electrically inactive tissue fails to produce an R wave in the overlying leads. This loss of normal progression is indicative of a loss of left ventricular muscle mass. The depolarization of the opposite wall in the opposite direction is then recorded negatively as a Q wave.
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Q waves are associated with myocardial infarction
Q waves are defined as the initial negative deflection of the QRS complex in an electrocardiogram, indicating a loss of positive electrical voltages due to localized necrosis of the heart muscle. This localized necrosis is often associated with myocardial infarction.
The Q wave results from the depolarization of the interventricular septum, which, under normal circumstances, occurs from the left ventricle to the right ventricle. The QRS complex represents ventricular depolarization and has a normal duration of 0.07 to 0.10 seconds. A wider QRS complex, ranging from 0.07 to 0.10 seconds, indicates abnormal conduction within the ventricles or a ventricular origin of an impulse.
Pathological Q waves are a sign of previous myocardial infarction. They are the result of the absence of electrical activity, creating an electrical "hole" due to electrically dead scar tissue. These Q waves typically take several hours to days to develop and, once present, rarely disappear. However, if the myocardial infarction is reperfused early, the stunned myocardial tissue can recover, and the pathologic Q waves may disappear.
The presence of pathological Q waves is a significant indicator of myocardial infarction, and they are often used to localize the infarct area. These Q waves are wider and deeper than normal Q waves and are referred to as pathological Q waves or Q-wave infarctions. They are typically associated with transmural infarction (STEMI) but may also be caused by extensive subendocardial ischemia (NSTEMI). Establishing a diagnosis of Q-wave infarction requires the presence of pathological Q waves in at least two anatomically contiguous leads.
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They are a sign of ventricular depolarization
The Q wave is a representation of the initial negative deflection of the QRS complex in an electrocardiogram. The QRS complex is a combination of three graphical deflections—the Q, R, and S waves—that occur in rapid succession on an ECG. The Q wave is any downward deflection immediately following the P wave.
The QRS complex represents ventricular depolarization. The depolarization of the ventricles generates three large vectors, which explains why the QRS complex is composed of three waves. The Q wave specifically results from the depolarization of the interventricular septum, which occurs from the left ventricle to the right ventricle. This process is referred to as ventricular septum depolarization.
The Q wave is a normal finding in most leads, representing the rapid depolarization of the thin septal wall between the two ventricles. However, pathological Q waves are often a consequence of myocardial infarction (MI). These waves are generally wider and deeper than normal Q waves and are markers of previous MIs, with subsequent fibrosis.
The presence of Q waves in specific leads can also provide important clinical insights. For example, Q waves in leads V1 to V4 with ST elevation can indicate acute MI, while the presence of Q waves in leads V1 to V3 can be indicative of a rare condition called congenitally corrected transposition of the great arteries.
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Pathologic Q waves occur when the electrical signal passes through scarred heart muscle
The Q wave is the initial negative deflection of the QRS complex in an electrocardiogram, which indicates a loss of positive electrical voltages due to localized necrosis of the heart muscle. This localized necrosis is often associated with myocardial infarction.
The QRS complex is the combination of three of the graphical deflections seen on a typical electrocardiogram. It is usually the central and most visually obvious part of the tracing. It corresponds to the depolarization of the right and left ventricles of the heart and the contraction of the large ventricular muscles. In adults, the QRS complex normally lasts 80 to 100 ms, while in children it may be shorter.
The Q wave specifically results from the depolarization of the interventricular septum, which under normal circumstances occurs from the left ventricle to the right ventricle. Generally, the Q wave should be no larger than 25% of the associated R wave. However, a pathologic Q wave is defined as having a deflection amplitude of 25% or more of the subsequent R wave, or being more than 0.04 seconds (40 milliseconds) in width and more than 2 millimetres in amplitude.
Pathologic Q waves occur when the electrical signal passes through stunned or scarred heart muscle. They are a sign of previous myocardial infarction and are the result of the absence of electrical activity. A myocardial infarction can be thought of as an electrical "hole" as scar tissue is electrically dead and therefore results in pathologic Q waves. These pathologic Q waves are not an early sign of myocardial infarction but generally take several hours to days to develop. Once they have developed, they rarely go away.
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Frequently asked questions
The Q wave represents the initial negative deflection of the QRS complex in an electrocardiogram, indicating a loss of positive electrical voltages due to localized necrosis of the heart muscle.
The QRS complex is the combination of three of the graphical deflections seen on a typical electrocardiogram. It is usually the central and most visually obvious part of the tracing. It corresponds to the depolarization of the right and left ventricles of the heart and the contraction of the large ventricular muscles.
A normal Q wave represents the rapid depolarization of the thin septal wall between the two ventricles and may be found in most leads. Pathological Q waves are a sign of previous myocardial infarction and are the result of the absence of electrical activity.
The Q wave is a small negative deflection that precedes the R wave. The R wave is the first upward deflection that appears in the QRS complex.
