We suggest that CRT might be considered for patients with new-onset high-degree AV block requiring chronic RV pacing, signs and/or symptoms of HF, and LVEF ≤ 45%.
(Conditional Recommendation, Moderate-Quality Evidence).

Values and preferences: This recommendation places value on the knowledge that CRT might provide more benefit than RV apical pacing, even though the strength of evidence is moderate and the available data result in a conditional rating.

Practical tip: Most patients in BLOCK HF had reduced LV systolic function (LVEF ≤ 45%) and symptomatic (NYHA class II/III) HF. Further, BLOCK HF enrolled patients with de novo implants and the same considerations might not apply in patients who are chronically RV-paced. (See Supplemental Tables S3 for further details.) There are limited randomized clinical trial (RCT) data with respect to CRT upgrade and potential benefits must be balanced with the significantly higher risk with CRT vs generator replacement alone.