Prognostic implication of Doppler echocardiographic derived coronary flow reserve in patients with left bundle branch block.

Aims: Myocardial ischaemia during pharmacological stress echocardiography is a strong prognostic predictor in patients with a left bundle branch block (LBBB). However, the additive value of Doppler-derived coronary flow reserve (CFR) during pharmacological stress testing remains to be investigated in this subset of patients.
Methods and Results: The study group consisted of 324 LBBB patients (187 men; age 68 ± 10 years) with known (n = 74) or suspected (n = 250) coronary artery disease who had undergone dipyridamole (up to 0.84 mg/kg over 6') stress echocardiography with CFR assessment of left anterior descending (LAD) by Doppler. A value of CFR ≤ 2.0 was considered abnormal. The median duration of follow-up was 15 months (first to third quartile: 8-34 months). Of the 324 patients, 52 (16%) had ischaemia at stress echo by wall motion criteria, and 139 (43%) had a CFR ≤ 2. During follow-up, 51 (16%) events occurred: 37 deaths and 14 myocardial infarctions (MIs). Age (HR: 1.09, 95% CI: 1.04-1.15, P < 0.0001), resting wall motion score index (HR: 5.29, 95% CI: 2.36-11.89, P < 0.0001), smoking habit (HR: 4.38, 95% CI: 1.93-9.91, P < 0.0001), and CFR ≤ 2 (4.69, 95% CI: 1.96-11.19, P = 0.001) were independently correlated with mortality, while CFR ≤ 2 (HR: 3.91, 95% CI: 1.90-8.04, P < 0.0001), age (HR: 1.06, 95% CI: 1.02-1.10, P = 0.001), smoking habit (HR: 2.25, 95% CI: 1.18-4.30, P = 0.01), ischaemia at stress echo (HR: 2.30, 95% CI: 1.11-4.77, P = 0.02), and resting wall motion score index (HR: 2.17, 95% CI: 1.11-4.25, P = 0.02) were independently correlated with death or MI. Four-year mortality and 4-year hard event rate were markedly higher in patients with CFR ≤ 2 than in those with CFR >2 (49 vs. 6% and 56 vs. 8%, respectively; P < 0.0001 for both). A CFR of ≤ 2 was associated with a significantly higher annual hard event rate independently of age, sex, ejection fraction, history of coronary artery disease, diabetes, and hypertension. Moreover, it was correlated with an increased (P < 0.0001) yearly mortality and event rate in patients with non-ischaemic stress echo conducted on therapy. At incremental analysis, a CFR of ≤ 2 added prognostic value to clinical findings, resting wall motion score index, ongoing anti-ischaemic therapy, and ischaemia at stress echo when both death and death or MI were the clinical endpoints.
Conclusions: Abnormal CFR on LAD is a strong and independent indicator of mortality and death or MI in patients with LBBB, and is associated with markedly increased risk also in the subset of patients with stress echo negative for ischaemia on therapy.