What is the QRS duration threshold used in CRT criteria?

• A. >200 ms
• B. <80 ms
• C. >120 ms
• D. >160 ms

Answer: (C)

The key concept is ventricular dyssynchrony shown by a widened QRS. QRS duration reflects how long it takes for ventricles to depolarize; a normal range is typically under about 100 ms. When the QRS is 120 ms or longer, it indicates significant conduction delay and often mechanical dyssynchrony, which CRT is designed to correct by pacing both ventricles to re-synchronize contraction. Therefore, the QRS duration threshold used to consider CRT is greater than 120 milliseconds. While very wide QRS (like >200 ms) signals severe conduction disease, the standard eligibility cut-off used in guidelines is 120 ms. A QRS narrower than 80 ms would not indicate the dyssynchrony CRT aims to fix.