The influence of heart rate on augmentation index and central arterial pressure in humans

1. Arterial stiffness is an important determinant of cardiovascular risk. A ugmentation index (AIx) is a measure of systemic arterial stiffness derived from the ascending aortic pressure waveform. The aim of the present study was to assess the effect of heart rate on AIx. We elected to use cardiac pa cing rather than chronotropic drugs to minimize confounding effects on the systemic circulation and myocardial contractility. 2. Twenty-two subjects (13 male) with a mean age of 63 years and permanent cardiac pacemakers in situ were studied. Pulse wave analysis was used to de termine central arterial pressure waveforms, non-invasively, during increme ntal pacing (from 60 to 110 beats: min(-1)), from which AIx and central blo od pressure were calculated. Peripheral blood pressure was recorded non-inv asively from the brachial artery 3. There was a significant, inverse, linear relationship between AIx and he art rate (r = -0.76; P < 0.001). For a 10 beats min(-1) increment, AIx fell by around 4%. Ejection duration and heart rate were also inversely related (r = -0.51; P < 0.001). 4. Peripheral systolic, diastolic and mean arterial pressure increased sign ificantly during incremental pacing. Although central diastolic pressure in creased significantly with pacing, central systolic pressure did not. There was a significant increase in the ratio of peripheral to central pulse pre ssure (P < 0.001), which was accounted for by the observed change in centra l pressure augmentation. 5. These results demonstrate an inverse, linear relationship between AIx an d heart rate. This is likely to be due to alterations in the timing of the reflected pressure wave, produced by changes in the absolute duration of sy stole. Consideration of nave reflection and aortic pressure augmentation ma y explain the lack of rise in central systolic pressure during incremental pacing despite an increase in peripheral pressure.