In CRT candidates, which QRS pattern is commonly observed?

• A. Left bundle branch block (LBBB)
• B. Atrial fibrillation
• C. Right bundle branch block (RBBB)
• D. Normal conduction

Answer: (A)

Left bundle branch block is the pattern most often seen in CRT candidates because CRT is specifically designed to correct the dyssynchrony caused by delayed left ventricular activation in LBBB. In LBBB, the left ventricle contracts later than the right ventricle, especially delaying the lateral wall, which reduces stroke volume and overall cardiac efficiency. By pacing both ventricles, CRT restores a coordinated contraction pattern, improving hemodynamics and symptoms. Other patterns, like right bundle branch block or normal conduction, don’t produce the same LV dyssynchrony that CRT targets, and atrial fibrillation is an arrhythmia rather than a QRS pattern, though CRT can be used in AF if overall criteria are met.