Pathophysiological aspects of carotid sinus massage

Abstract

Aims: We studied the blood pressure (BP) decrease after carotid sinus massage to study cardioinhibition (CI) and arterial vasodepression (aVD), whether CI and aVD occur independent of one another, and how the BP decrease ends.

Methods and results: We measured BP, heart rate (HR), stroke volume, and total peripheral resistance (TPR) retrospectively in carotid sinus massage cohorts in two Dutch syncope centres. Cardioinhibition and aVD were defined as HR and TPR decreasing below 3 SD under pre-massage baseline means. We used the logratio method to analyse changes relative to baseline and tested whether CI and aVD occurred together more often than through chance and whether the responses depended on massage duration and on corrective BP increases. Cardioinhibition occurred in 48% and aVD in 30% of 244 massages of 90 persons. Cardioinhibition and aVD did not occur together more often than randomly. Compared with aVD, CI occurred more often, earlier, faster, and shorter with a larger maximal but similar overall BP-decreasing effect. Longer massage duration yielded a larger BP decrease through stronger aVD. The BP decrease evoked corrective increases of HR and TPR.

Conclusion: Cardioinhibition appears as a phasic response to the onset of massage, independent of aVD, which is a more latent response sensitive to ongoing massage. Blood pressure corrections probably depend on the contralateral carotid sinus and aortic baroreceptors. The BP decrease after sinus massage may in part depend on the efficacy of corrective responses.

Keywords: Baroreflex; Cardioinhibition; Carotid sinus massage; Syncope; Vasodepression.

Graphical Abstract

Figure 1

Analysis scheme. Example HR data are shown for two individual massages, in red (the one with the large decrease) and blue. The top panel shows HR in beats per minute, and the bottom panel shows corresponding logratio values. The top panel shows the 45-s pre-massage period used to calculate the mean and SD of individual HR data. The figure shows a 3 SD zone above and below mean HR. The 45 s after onset of massage form the ‘early period’, in which points of minimum HR were identified. The amplitude of HR at the minima was expressed as the difference from baseline divided by SD, i.e. a Z-score. Z-scores larger than −3 were regarded as ‘obscure’ peaks (example in blue), and Z-scores < −3 were considered ‘overt’ (example in red). The bottom panel shows logratio values. The mean of all valid samples in the early period was the ‘sustained magnitude’ of the early period; here, only some samples are indicated by vertical lines. The sustained amplitude of the late period (45–90 s after onset of massage) was calculated similarly. HR, heat rate.

Figure 2

Overall logratio effects of responses to carotid sinus massage. Logratio values are shown for all massages (left) and for massages with at least one overt HR or TPR response (right). In these logratio diagrams, mean MAP_LR (black lines) represents the sum of the means of HR_LR (red area), SV_LR (blue area), and TPR_LR (green area). Likewise, the logratio of mean cardiac output (CO_LR; purple dotted line) is the sum of HR_LR and SV_LR. Top panels show cumulative areas of HR, SV, and TPR, meaning all BP-increasing effects for any point in time are stacked upwards starting at the horizontal zero line; likewise, BP-decreasing effects are shown stacked downwards. Parameters were stacked away from baseline in the following order: HR_LR, TPR_LR, and SV_LR. Bottom panels show overlaid means for the same data. CO_LR and MAP_LR are shown as overlaid lines in all graphs. Note that the negative BP-decreasing HR_LR peak occurs earlier than the TPR_LR peak and that minimum BP occurs between the HR and aVD peaks.

Figure 3

Logratio effects of massage duration. Massages shorter than the median duration are shown at the left and longer ones at the right. The presentation is similar to previous figures. Only the early analysis period is shown. The number of ongoing massages is shown as ‘duration’, with the axis indicated at the right-hand side. Note that HR responses show no appreciable differences between shorter and longer massages, while TPR responses to longer massages were more negative (i.e. decreased more) and lasted longer, together producing stronger aVD. HR, heart rate; TPR, total peripheral resistance; SV, stroke volume.

Figure 4

Groups divided by CI and aVD. Four groups were formed by whether responses showed CI and aVD or not. The top panels show logratios of HR (red), SV (blue), and TPR (green) as cumulative areas as in Figure 3. The bottom panels show overlaid logratio means. The purple dotted line shows CO as the sum of logratios of HR and SV. The dotted vertical line at 45 s after onset of massage divides the early and late periods of analysis. Results are interpreted in the main text. The green arrow in the pure CI panel shows where mean TPR first becomes positive as proof of a corrective effect, ∼30 s after onset of massage. The red arrow in the pure aVD panel shows when HR first became positive as proof of a corrective BP-increasing effect, ∼15 s after onset of massage. aVD, arterial vasodepression; CI, cardioinhibition.