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Q Wave

Q wave

Limb Leads and Q Wave

• Limb leads (I, II, III, aVF, aVR, aVL)
• View the heart in the frontal plane
• The ventricles are activated in the following order:
1. Interventricular septum (V_S - septal vector)
2. Left and right ventricles (V_M - main vector)
3. Apex of the left ventricle (V_T - terminal vector)
• Interventricular septum vector (V_S)
• Points away from leads aVL, I (sometimes also from lead II)
• And creates a Q wave
• Main cardiac vector (V_M)
• Points away from leads aVR and III (partially from III)
• Thus, a Q wave can sometimes be seen in aVR and III
• This Q wave occurs with left axis deviation
• V_M vector rotates towards lead I
• In obese individuals, the heart (V_M) changes position with breathing
• And creates a position-related Q wave

ECG and Q Wave

• Width < 0.03s (< 1 small square)
• Depth < 3mm (< 3 small squares)
• Only in aVR and III may exceed 3mm
• This is a normal variant (related to the main ventricular vector)
• Does not exceed 1/4 of the R wave in the given lead
• Common in lateral leads (aVL, I, V5, V6)
• Should not be present in leads V1-V3

Variants of the Q Wave

Nomenclature of the QRS Complex

• Uppercase letters (Q, R, S) denote the dominant deflections of the QRS complex (QRS complex nomenclature)
• Lowercase letters (q, r, s) denote deflections smaller than 1/2 of the dominant QRS complex deflection
• Q Wave is the first negative deflection of the QRS complex
• QS Complex is a completely negative QRS complex

Physiological Q Wave and Sinus Rhythm

• The EKG shows a sinus rhythm
• Q wave is present in (II, III, aVF, V4-V6)
• Width < 0.03 s
• Depth < 3 mm
• Q wave in aVR lead may have pathological dimensions
  • The main cardiac vector (V_M) points directly away from lead aVR (partially from lead III)
  • A large negative Q wave appears in aVR (sometimes in lead III)
  • However, in this aVR lead, there is an rS configuration
    • Before the deep S wave, there is a small r wave - which results from depolarization of the ventricular septum: V_S vector

Positional Q Wave

• If a patient has a high diaphragm (obesity, when lying down, during exhalation)
• The main cardiac vector (V_M) is rotated upward and to the left and points away from lead III
• A pathological Q wave can occur in lead III
• Width > 0.03 s
• Depth > 3 mm
• Q wave may also appear in adjacent leads (II, aVF)
• but in these leads, it does not usually have pathological parameters
  
  
• Positional Q waves can appear in patients who take deep breaths during EKG recording (changing the cardiac axis)
• It appears during exhalation
• It disappears during inhalation
• If the patient has had a lower infarction, then pathological Q waves (II, III, aVF) are present regardless of breathing
  
  
• If pathological Q waves disappear with deep inhalation from lead III
• then it is physiological Q (a variant of normal)

Positional (Respiratory) Q Wave

• Deep exhalation
• The diaphragm rises and the apex of the heart rotates upward and to the left
• The main cardiac vector also rotates upward and to the left thus pointing away from lead III
• Q wave appears in lead III
• Deep inhalation
• The diaphragm descends, and the apex of the heart rotates downward and to the right
• The main cardiac vector also rotates downward and to the right thus starting to point toward lead III
• R wave increases
• and Q wave disappears
• This cycle repeats with deep breathing, meaning the Q wave in lead III appears and disappears
• This is a positional (respiratory) Q wave