Background: The QKD interval is the time between the QRS wave on the electrocardiogram (ECG) and the detection of the last Korotkoff sound during BP measurement. Measurement of the QKD interval during ambulatory blood pressure (BP) monitoring provides an automatic evaluation of arterial stiffness. The objective of this longitudinal study was to examine the relationship between arterial stiffness assessed by this method and the occurrence of cardiovascular complications in a cohort of initially untreated hypertensive patients.
Methods: The initially untreated hypertensive patients were included in the cohort of hypertensives recruited to our center between January 1992 and December 1999. All benefited from ambulatory measurement of the QKD interval and BP over 24 h. Most of these patients were given antihypertensive treatment and were followed up by their family physicians, who were unaware of the QKD results. Their outcome was evaluated in 2003 by inquiring of the patients themselves or of their family physicians.
Results: The initial population comprised 412 patients. At the end point, 33 had been lost to follow-up. We recorded 49 cardiovascular events in this population with an average follow up of 65 +/- 36 months. In a Cox model, the arterial stiffness assessed by the QKD(100-60) as a percentage of the height-predicted normal value was significantly associated with the occurrence of cardiovascular complications, independent of age and mean 24-h BP.
Conclusions: This study using ambulatory measurement of the QKD interval showed that an increase in arterial stiffness was a marker of cardiovascular risk. We show for the first time that its value persists after taking account of the mean systolic pressure over 24 h.