Neurally mediated syncope and cardiac beta-adrenergic receptor function

Syncopes and clinical outcome in heart failure: results from prospective clinical study data in Germany

AIMS

Whereas syncopal episodes are a frequent complication of cardiovascular disorders, including heart failure (HF), little is known whether syncopes impact the prognosis of patients with HF. We aimed to assess the impact of a history of syncope (HoS) on overall and hospitalization-free survival of these patients.

METHODS AND RESULTS

We pooled the data of prospective, nationwide, multicentre studies conducted within the framework of the German Competence Network for Heart Failure including 11 335 subjects. Excluding studies with follow-up periods <10 years, we assessed 5318 subjects. We excluded a study focusing on cardiac changes in patients with an HIV infection because of possible confounding factors and 849 patients due to either missing key parameters or missing follow-up data, resulting in 3594 eligible subjects, including 2130 patients with HF [1564 patients with heart failure with reduced ejection fraction (HFrEF), 314 patients with heart failure with mid-range ejection fraction, and 252 patients with heart failure with preserved ejection fraction (HFpEF)] and 1464 subjects without HF considered as controls. HoS was more frequent in the overall cohort of patients with HF compared with controls (P < 0.001)-mainly driven by the HFpEF subgroup (HFpEF vs. controls: 25.0% vs. 12.8%, P < 0.001). Of all the subjects, 14.6% reported a HoS. Patients with HFrEF in our pooled cohort showed more often syncopes than subjects without HF (15.0% vs. 12.8%, P = 0.082). Subjects with HoS showed worse overall survival [42.4% vs. 37.9%, hazard ratio (HR) = 1.21, 99% confidence interval (0.99, 1.46), P = 0.04] and less days alive out of hospital [HR = 1.39, 99% confidence interval (1.18, 1.64), P < 0.001] compared with all subjects without HoS. Patients with HFrEF with HoS died earlier [30.3% vs. 41.6%, HR = 1.40, 99% confidence interval (1.12, 1.74), P < 0.001] and lived fewer days out of hospital than those without HoS. We could not find these changes in mortality and hospital-free survival in the heart failure with mid-range ejection fraction and HFpEF cohorts. HoS represented a clinically high-risk profile within the HFrEF group-combining different risk factors. Further analyses showed that among patients with HFrEF with HoS, known cardiovascular risk factors (e.g. age, male sex, diabetes mellitus, and anaemia) were more prevalent. These constellations of the risk factors explained the effect of HoS in a multivariable Cox regression models.

CONCLUSIONS

In a large cohort of patients with HF, HoS was found to be a clinically and easily accessible predictor of both overall and hospitalization-free survival in patients with HFrEF and should thus routinely be assessed.

Cardiac autonomic dysfunction in patients with head-up tilt test-induced vasovagal syncope

BACKGROUND

Vasovagal syncope (VVS) is the result of an autonomic reflex that has a final effect of reducing sympathetic drive and increasing vagal activity. However, whether syncopal symptoms are associated with pathological cardiac autonomic modulation is not fully known. We tested the hypothesis that cardiac autonomic function is impaired in patients with VVS.

METHODS

Eighty-four consecutive patients (59 males; 48.8 ± 20.9 years) with recurrent unexplained syncope were enrolled. The head-up tilt test (HUTT) was positive in 38 patients and negative in 46 patients. Cardiac autonomic function was assessed by baroreflex sensitivity (BRS), heart rate variability, plasma concentrations of norepinephrine, and (123) I-metaiodobenzylguanidine (MIBG) scintigraphy.

RESULTS

BRS indices were significantly lower in the HUTT-positive group than in the HUTT-negative group (6.1 ± 5.5 mm Hg/s vs 9.8 ± 7.6 mm Hg/s, P = 0.02). With regard to cardiac (123) I-MIBG scintigraphy, the mean heart-to-mediastinum ratio at the delayed phase tended to be lower in HUTT-positive than in HUTT-negative individuals, but this difference was not significant (2.75 ± 0.55 vs 3.02 ± 0.49, P = 0.08).The percent washout rate of (123) I-MIBG was significantly higher in the positive group compared with the negative group (40.7 ± 13.1% vs 31.5 ± 13.3%, P = 0.02). Multivariate logistic analysis revealed that the appearance of HUTT-induced VVS was predicted independently by a high percent washout rate of (123) I-MIBG (odds ratio, 0.954; 95% confidence interval, 0.903-0.998; P = 0.048).

CONCLUSIONS

Our results suggest that pathological autonomic cardiac modulation may play a role in the appearance of syncope in VVS patients.

Basic autonomic nervous function in patients with neurocardiogenic syncope

Basic autonomic nervous function was evaluated in patients with neurocardiogenic syncope (NCS). Atropine, isoproterenol, propranolol, phenylephrine, and phentolamine were administered successively, and parasympathetic nerve activity and beta- (and alpha-) activity, sensitivity, and secretion of the sympathetic nerve were determined in patients with NCS and control subjects. In patients with NCS, beta- and alpha- sensitivity were higher and beta-activity and beta- and alpha-secretion lower than in control subjects. In patients with NCS, the increased basic beta-sensitivity may contribute to induce strong cardiac contractions and augment ventricular mechanoreceptor response, and a compensatory state against diminished neuronal sympathetic activity is suggested by the increased alpha-sensitivity.

Increased expression of adenosine A2A receptors in patients with spontaneous and head-up-tilt-induced syncope

BACKGROUND

Adenosine may play a role in the triggering of neurocardiogenic syncope, but no information on adenosine receptors is available at the present time.

OBJECTIVE

The purpose of this study was to investigate whether adenosine A2A receptors expression is altered in patients with neurocardiogenic syncope.

METHODS

Adenosine plasma levels (APLs), the expression of A2A receptors, were measured (mean +/- standard error of the mean) during tilt testing. Expression of receptors was assessed on mononuclear cells using a selective receptor ligand.

RESULTS

At baseline, the APLs of 16 patients with a positive test were higher than those of 17 patients with a negative test and of those of a control group (2.10 +/- 0.30 vs. 0.40 +/- 0.05 and 0.41 +/- 0.06 muM, respectively; P <.0001). The number of receptors was higher in patients tested positive than in patients tested negative or in the control group (122 +/- 10 vs. 38 +/- 4 and 44 +/- 4 fmol/g of proteins, respectively; P <.0001). No difference was found in the affinity or synthesis among the three groups.

CONCLUSION

This study showed an increased number and an up-regulation of adenosine A2A receptors in patients with spontaneous syncope and a positive head-up tilt, which in the context of high APLs may play a role in the recurrence of syncopal episodes.

Drug treatment of orthostatic hypotension and vasovagal syncope

Orthostatic hypotension is a common problem, estimated to occur in 5 out of every 1000 individuals and in as many as 7% to 17% of patients in an acute care setting. Moreover, orthostatic hypotension may be more prominent in elderly patients due to the increased intake of vasoactive medications and concomitant decrease in physiologic function, such as baroreceptor sensitivity, often seen with aging. Orthostatic hypotension is a fall in blood pressure on assuming an upright position. Absolute cutoffs for the drop in blood pressure are often difficult to determine because different patients exhibit varying degrees of tolerance to falls in blood pressure. Therefore, strict numerical criteria may lead to underdiagnosis and improper intervention. A thorough review of patient symptomatology combined with appropriate clinical tests should be employed to narrow the vast differential diagnosis and pinpoint the etiology. The fall in blood pressure seen in orthostatic hypotension results from the inability of the autonomic nervous system to adequately compensate for the 500 mL blood that is estimated to pool in the lower extremities on assuming an upright posture. The decrease in venous return results in a concomitant decrease in cardiac output and thus hypoperfusion of the cerebral circulation, possibly resulting in syncope or various other symptoms. A complete investigation should consider hypovolemia, removal of offending medications, primary autonomic disorders, secondary autonomic disorders and, of course, vasovagal syncope, the most common cause of syncope. Although further research is still necessary to rectify the disease process responsible for orthostatic hypotension, patients suffering from this disorder can effectively be treated through a combination of nonpharmacologic treatment, pharmacologic treatment and patient education. Agents such as fludrocortisone, midodrine and erythropoietin show promising results as therapeutic adjuncts. Treatment for recurrent vasovagal syncope includes increased salt intake, and various drug treatments, most of which are still under investigation.