Prognostic value of QKD interval corrected by QRS duration in hypertensive patients

Objectives: the QKD interval is measured between the onset of QRS on the ECG and detection of last Korotkoff sound by a microphone placed on the brachial artery while measuring BP. It is the sum of preejection time and pulse transmission time and thus is correlated to pulse wave velocity (PWV). This interval is automatically monitored with BP and HR every 15 minutes during 24 h with an ambulatory blood pressure monitoring device (Diasys integra, Novacor, France). The 96 measurements obtained allow to automatically calculate the QKD(100-60), QKD value for 100 mmHg SBP and 60 bpm HR. This indice of arterial stiffness has been shown to be linked to future cardiovascular (CV) events, independently of 24 h BP. However this interval may be abnormally prolonged in case of left bundle branch blocks (LBBB). Methods: we tested the effects of simply removing QRS duration from QKD(100-60) value on the prediction of CV events in a population of 412 hypertensives (247 males; age = 53 +/- 14 years; office BP = 158 +/- 19/97 +/- 11 mmHg; 24 h BP = 133 +/- 17/86 +/- 11 mmHg) followed prospectively. Results: mean follow up was 65 months, 32 pts were lost, 49 CV events occurred including 11 deaths. Cox model showed that baseline QKD(100-60) (m=202 +/- 19; 142-254 ms) was significantly (p < 0.05) associated to events independently of age, 24h SBP and other traditional risk factors. Removing QRS duration (m=85 +/- 10; 61-158 ms) improves the relation to events (monovariate khi(2)=38 vs 30). Conclusion: removing QRS duration from QKD(100-60) improves its predictive value of future CV events and allows using this method in patients with LBBB.