Ambulatory measurement of the Qkd interval normalized to heart rate and systolic blood pressure to assess arterial distensibility – value of Qkd 100–60

Background Reduced distensibility of large arteries plays an important role in cardiovascular risk. Determination of the QKD interval during the ambulatory measurement of blood pressure enables calculation of an index of arterial distensibility. This index, the QKD 100–60 , is the theoretical value of QKD at systolic blood pressure of 100 mmHg and heart rate of 60 bpm obtained from the linear bivariate relationship linking QKD, systolic blood pressure and heart rate on a hundred successive values measured over 24 h. This study was designed to examine the relationship between QKD and QKD 100–60 on heart rate and systolic function of the left ventricle, the two parameters governing the pre-ejection time which is part of the QKD interval. Methods and results In a population of 203 untreated hypertensive patients having benefited from an ambulatory measurement of blood pressure over 24 h with QKD monitoring and an M-mode echocardiographic recording of the left ventricle, we found that although mean QKD was linked to heart rate and systolic function of the left ventricle, QKD 100–60 was not. It fell significantly with age, and to a greater extent in the sustained hypertensives than in white-coat hypertensives. Conclusion QKD 100–60 constitutes an index of arterial distensibility independent of the pre-ejection time. As an adjunct to the ambulatory measurement of blood pressure, its determination is simple and completely automatic, thus eliminating observer bias.