The ECG strip below shows normal sinus rhythm, then atrial fibrillation with a rapid ventricular response develops. With the faster heart rate, the QRS complex morphology changes to that of a LBBB. As sinus rhythm restores, and the ventricular rate slows, the QRS morphology returns to normal.
What causes a LBBB?
A left bundle branch block usually is a sign of an underlying heart disease, including dilated cardiomyopathy, hypertrophic cardiomyopathy, high blood pressure, aortic valve disease, coronary artery disease and other heart conditions. While left bundle branch block can appear in healthy people, it most often does not.
What causes intermittent left bundle branch block?
Intermittent left bundle branch block (LBBB) has been reported in the literature following certain conditions such as cardiac blunt trauma, myocardial infarction (MI) or exercise induced LBBB. In the majority of cases, the patients usually have underlying coronary arteries disease.
Is LBBB always pathological?
Clinical implications of left bundle branch block (LBBB) Left bundle branch block is always pathological. It affects left ventricular contractility and pumping function.
Can LBBB cause chest pain?
Background: Intermittent left bundle branch block (LBBB) has been linked to chest pain, and causes cardiac memory electrocardiographic (ECG) changes mimicking ischemia.
What is the meaning LBBB?
Introduction. Left bundle branch block (LBBB) is a common electrocardiographic (ECG) abnormality seen in patients whose normal cardiac conduction down both anterior and posterior left fascicles of the His-Purkinje system is compromised.
Does LBBB cause shortness of breath?
For others, however, a delay in the arrival of electrical impulses to the heart’s left ventricle can cause syncope (fainting), due to unusual heart rhythms that affect blood pressure. Some people might also experience something called presyncope.
Why are septal Q waves absent in LBBB?
Because left ventricular activation is delayed in LBBB and the initial septal activation is from right to left (opposite of the normal situation), septal Q waves indicative of an MI are absent. Additionally, secondary ST-T wave abnormalities that occur in LBBB obscure the recognition of injury currents in ischemia and infarction.
What is the direction of septal depolarization in LBBB?
Normally the septum is activated from left to right, producing small Q waves in the lateral leads. In LBBB, the normal direction of septal depolarization is reversed (becomes right to left), as the impulse spreads first to the RV via the right bundle branch and then to the left ventricle via the septum.
What is the normal direction of QRS in LBBB?
In LBBB, the normal direction of septal depolarization is reversed (becomes right to left), as the impulse spreads first to the RV via the right bundle branch and then to the left ventricle via the septum. This sequence of activation prolongs the QRS duration to ≥120 ms and eliminates the normal septal Q waves in the lateral leads.
What causes QRS to be prolonged in left ventricles?
Because the left bundle branch is dysfunctional, the impulse will spread (through the left ventricle) partly or entirely outside of the conduction system; such impulse conduction is slow and therefore the QRS duration becomes prolonged.
