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Dr. Ajith Kumar J MD
Dept. of Emergency Medicne
Travancore Medicity, Kollam
India
editor
Delayed depolarisation of ventricular myocardium in patients with LBBB with following
QRS complex >0.12s
broad QS or rS pattern in the right precordial leads (V1,V2,V3)
Monophasic R wave in lateral lead , absence of q wave in lateral leads.
Pathophysiology
In LBBB the ventricles are activated from right to left leading to absence of r wave in V1 & q wave in V6 .This results in negative QRS in right chest leads and a positive wave in left chest leads with wide QRS.
With LBBB, the QS wave in lead V1 sometimes shows a small notch at its point, producing W shape. Similarly, the broad R wave in lead V6 may show a notching at its peak, giving it a distinctive M shape.
Clinical Significance
Advanced coronary artery disease
Valvular heart disease
Hypertensive heart disease
Cardiomyopathy
Note that ECG shows QS pattern in right chest leads with discordance.
LBBB & MI
Characteristically in,LBBB the affected leads also feature discordance of the ST segment /T wave complex . When major QRS vector is directed downward the ST segment will be elevated & T wave will be prominently positive. Similarly, if major QRS vector is directed upwards, ST segment will be depressed & T wave will be inverted. Lose of this pattern is a clue to Acute MI.
Sgarbossa's criteria for STEMI in the presence of LBBB
ST segment elevation ≥1mm concordant with QRS complex (score 5)
ST segment depression ≥1mm in leads V1,V2 or V3(Score 3)
ST segment elevation ≥5mm discordant to QRS complex (Score 2)
Score of ≥3 points established the diagnosis of acute MI with 90% specificity.
Normal Ventricular Activation
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RBBB
RBBB in ECG is characterized by
Lead V1 shows an rSR' pattern with a wide R' wave.
Lead V6 shows a qRS pattern with a wide S wave.
It can be either complete (QRS >0.12 sec)or incomplete (<0.12 sec)
RBBB: ECG shows rSR' pattern over the right side chest leads.
Pathophysiology
The interventricular septum is activated first . The left side is stimulated first . On a normal ECG it represented as r wave in V1 & a small septal q wave in V6.
The second phase of ventricular stimulation is the simultaneous depolarisation of the left and right ventricles. This results in a deep S wave in V1 & tall R wave in V6 . In RBBB there is increased time for stimulation of right ventricle resulting in widening of QRS complex.
The third phase is due to delayed depolarisation of the right ventricle. The electrical voltages in third phase are directed to right leading to a positive wide deflection R'. the rightward spread produces a negative wave in V6.
Clinical Significance
ASD with right to left shunt
COPD
Pulmonary artery hypertension
Pulmonary stenosis
Pulmonary Embolism
Updated on 8/9/2015
Reference : Goldberger's Clinical ECG
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emmedonline
Dr. Ajith Kumar J MD
Dept. of Emergency Medicne
Travancore Medicity, Kollam
India
editor