Paradoxical vasodilation during lower body negative pressure in patients with vasodepressor carotid sinus syndrome

Cardiac Iodine-123-Meta-Iodo-Benzylguanidine Uptake in Carotid Sinus Hypersensitivity

Background

Carotid sinus syndrome is the association of carotid sinus hypersensitivity with syncope, unexplained falls and drop attacks in generally older people. We evaluated cardiac sympathetic innervation in this disorder in individuals with carotid sinus syndrome, asymptomatic carotid sinus hypersensitivity and controls without carotid sinus hypersensitivity.

Methods

Consecutive patients diagnosed with carotid sinus syndrome at a specialist falls and syncope unit were recruited. Asymptomatic carotid sinus hypersensitivity and non-carotid sinus hypersensitivity control participants recruited from a community-dwelling cohort. Cardiac sympathetic innervation was determined using Iodine-123-metaiodobenzylguanidine (123-I-MIBG) scanning. Heart to mediastinal uptake ratio (H:M) were determined for early and late uptake on planar scintigraphy at 20 minutes and 3 hours following intravenous injection of 123-I-MIBG.

Results

Forty-two subjects: carotid sinus syndrome (n = 21), asymptomatic carotid sinus hypersensitivity (n = 12) and no carotid sinus hypersensitivity (n = 9) were included. Compared to the non- carotid sinus hypersensitivity control group, the carotid sinus syndrome group had significantly higher early H:M (estimated mean difference, B = 0.40; 95% confidence interval, CI = 0.13 to 0.67, p = 0.005) and late H:M (B = 0.32; 95%CI = 0.03 to 0.62, p = 0.032). There was, however, no significant difference in early H:M (p = 0.326) or late H:M (p = 0.351) between the asymptomatic carotid sinus hypersensitivity group and non- carotid sinus hypersensitivity controls.

Conclusions

Cardiac sympathetic neuronal activity is increased relative to age-matched controls in individuals with carotid sinus syndrome but not those with asymptomatic carotid sinus hypersensitivity. Blood pressure and heart rate measurements alone may therefore represent an over simplification in the assessment for carotid sinus syndrome and the relative increase in cardiac sympathetic innervation provides additional clues to understanding the mechanisms behind the symptomatic presentation of carotid sinus hypersensitivity.

Symptomatic presentation of carotid sinus hypersensitivity is associated with impaired cerebral autoregulation

Background

Carotid sinus hypersensitivity (CSH) is associated with syncope, unexplained falls, and drop attacks in older people but occurs asymptomatically in 35% of community‐dwelling elders. We hypothesized that impaired cerebral autoregulation is associated with the conversion of asymptomatic CSH to symptomatic CSH. We therefore conducted a case–control study evaluating individuals with CSH with and without the symptoms of syncope or unexplained falls, as well as non‐CSH controls, to determine whether the blood pressure and heart rate changes associated with CSH are associated with symptoms only when cerebral autoregulation is altered.

Methods and Results

Bilateral middle cerebral artery blood flow velocities (BFV) were measured in consecutive patients with symptomatic CSH (n=22) and asymptomatic controls with (n=18) and without CSH (n=14) using transcranial Doppler ultrasonography during lower body negative pressure‐induced systemic hypotension. Within‐group comparisons revealed significantly lower cerebrovascular resistance index (CVR_i) at nadir for the asymptomatic CSH group (right, mean [95% CI]: 2.2 [1.8, 2.8] versus 2.6 [2.2, 3.0]; P=0.005; left: 2.8 [2.4, 3.3] versus 3.1 [2.7, 3.8]; P=0.016). Between‐group comparisons showed higher mean BFV (right: estimated mean difference, B=5.49 [1.98, 8.80], P=0.003; left: 4.82 [1.52, 8.11], P=0.005) and lower CVR_i (right: B=0.08 [0.03, 0.12], P=0.003, left: B=0.07 [0.02, 0.12], P=0.006) in asymptomatic CSH versus symptomatic CSH groups. There were no significant differences in bilateral mean BFV or right CVR_i between the non‐CSH and symptomatic CSH groups but differences were present for left CVR_i (B=0.07 [0.02, 0.013], P=0.015).

Conclusion

Cerebral autoregulation is altered in symptomatic CSH and therefore appears to be associated with the development of hypotension‐related symptoms in individuals with CSH.

Results of carotid sinus massage in a tertiary referral unit--is carotid sinus syndrome still relevant?

BACKGROUND

carotid sinus hypersensitivity (CSH) is associated with syncope, drop attacks and unexplained falls in older people. However, a recent study has also reported a prevalence of 35% in asymptomatic community-dwelling older people.

OBJECTIVE

we conducted a retrospective observational study to investigate the haemodynamic and symptom responses of a large cohort of patients undergoing carotid sinus massage (CSM).

METHODS

the electronically stored haemodynamic data of 302 consecutive patients, aged 71 +/- 11 years, investigated with CSM for unexplained falls and syncope was analysed. Bilateral sequential CSM was performed in the supine and upright positions with continuous electrocardiogram (ECG) and non-invasive beat-to-beat blood pressure monitoring (Taskforce, CN Systems, Austria). CSH (CSH) was defined by maximal R-R interval > or =3 s (cardioinhibitory) and/or a systolic blood pressure drop of > or =50 mmHg (vasodepressor).

RESULTS

a total of 74/302 (25%) subjects had CSH, 37 (50%) of which were cardioinhibitory (CI) and 37 (50%) were vasodepressor (VD) subtypes. Subjects with positive CSM were significantly older (75.2 vs 70.2 years, P < 0.001), and more likely to be male (32% vs 19%, P < 0.01). CSH was diagnosed with right-sided CSM alone in 45 (61%) subjects and erect CSM only in 36 (49%) subjects. Symptom reproduction was more likely with the CI than the VD subtypes (82% vs 28%; P < 0.001).

CONCLUSION

CSH was diagnosed in 25% of patients investigated with CSM at our specialist unit, lower than the prevalence of 39% reported for community-dwelling older individuals. This discrepancy may be explained by selection bias and demographic differences, but raises the possibility of CSH being an age-related epiphenomenon rather than a causal mechanism for syncope, drop attacks and unexplained falls. Our observations have important implications for clinical practice and the development of future research strategies.

Treatment of vasodepressor carotid sinus syndrome with midodrine: a randomized, controlled pilot study

OBJECTIVES

To evaluate the efficacy of treatment of the vasodepressor form of carotid sinus hypersensitivity (carotid sinus syndrome (CSS)) with midodrine.

DESIGN

A prospective, double-blind, randomized, controlled trial of crossover design.

SETTING

A dedicated outpatient facility with access to tilt-table, digital arterial photoplethysmography, and 24-hour ambulatory blood pressure (BP) monitoring equipment.

PARTICIPANTS

Ten older adults (4 male, 6 female, mean age 75, range 66-86 years) with a history of unexplained syncope who displayed an asymptomatic decrease in systolic BP (SBP) of more than 50 mmHg or a symptomatic decrease of more than 30 mmHg within 30 seconds of carotid sinus massage (CSM).

MEASUREMENTS

Symptom reproduction and BP and heart rate changes were evaluated after CSM in supine and semierect positions on the right and then left sides. These measurements were performed on the final day of placebo and active-treatment phases. Ambulatory 24-hour BP monitoring took place on the penultimate and final days of each treatment phase.

RESULTS

Eight patients were symptomatic after their initial CSM. The mean+/-standard deviation SBP decrease after initial CSM was 54+/-22 mmHg. Initial mean 24-hour ambulatory BP was 127/70+/-7/5 mmHg. Eight patients reported symptoms after CSM at the end of the placebo phase. The mean SBP decrease at the end of the placebo phase was 49+/-12 mmHg. The mean 24-hour ambulatory BP was 127/69+/-9/7 mmHg. One patient reported symptoms after CSM at the end of the active-treatment phase. The mean SBP decrease at the end of the active-treatment phase was 36+/-9 mmHg. The mean 24-hour ambulatory BP at the end of the treatment phase was 133/75+/-7/6 mmHg. The differences in symptom reporting and mean SBP decrease after CSM were both significant (P<.01 and P=.03, respectively).

CONCLUSION

The results of this pilot study suggest that treatment of vasodepressor CSS with midodrine significantly reduced the rate of symptom reporting and attenuated SBP decreases after CSM but increased mean 24-hour ambulatory BP.