Methods
We studied consecutive patients with vasovagal syncope seen at the Syncope Unit of the National Cardiology Institute of Mexico between June 2009 and June 2012. The age limit of the studied population was arbitrarily set from 15 to 50 years in an effort to exclude younger children that could possibly convey unreliable history as well as older adults that could have additional causes for their fainting spells.
Vasovagal syncope was defined as a transient loss of consciousness characterized by a rapid onset, short duration, and spontaneous complete recovery. All potential cases underwent a medical examination that ruled out other causes of fainting spells such as structural heart disease, arrhythmias, disorders in the electrical conduction of the heart, cerebrovascular disease, epilepsy, thyroid abnormalities, head trauma, or the use of illegal drugs. None of the participants were taking any medication that could affect autonomic nervous system performance.
Informed consent was obtained from all participants. In case of minors, consent was also obtained from a parent. The study was approved by the Ethics and Research Committee of the National Institute of Cardiology in Mexico.
Methods
As part of their routine diagnostic workup, all cases underwent a head-up tilt test. Type of syncope was classified according to VASIS criteria as follows: (a) classic vasovagal syncope pattern defined as an abrupt fall in blood pressure suggesting sympathetic withdrawal, accompanied by decrease in heart rate, which coincides with, or follows shortly after, the decrease in blood pressure; (b) orthostatic intolerance pattern characterized by a slow but progressive fall in blood pressure, which begins immediately after assumption of the upright position and lasts until the end of the test. In the orthostatic intolerance response, there is no clear vasovagal reaction or a decrease in heart rate. Systolic pressure decreases to values less than 80 mm Hg, and therefore, symptoms of hypotension such as dizziness, blurring of vision, lightheadedness, and sweating occur, which persist for several minutes until the end of the test, but complete loss of consciousness does not occur for at least 5 minutes from the onset of the symptoms, at which time the test is interrupted. These 2 responses were observed under basal conditions or after pharmacological challenge with 5 mg of sublingual isosorbide if required.
All participants filled out a brief questionnaire about the age at the first syncopal episode, the number of fainting spells, and the date of the last episode. In addition, all participants filled out a validated Spanish version of the Fibromyalgia Impact Questionnaire (FIQ) and the Composite Autonomic Symptoms and Signs (COMPASS) questionnaire. Fibromyalgia Impact Questionnaire is an instrument designed to estimate the overall impact of FM over many dimensions (e.g., function, pain level, fatigue, sleep disturbance, and psychological distress). It is scored from 0 to 100, with the latter number being the worst case. The average score for patients seen in tertiary care settings is about 50. The COMPASS questionnaire explores symptoms related to 9 different autonomic function domains: orthostatic, secretomotor, male sexual dysfunction, urinary, gastrointestinal, pupillomotor, vasomotor, syncope, and sleep function. The worst possible overall count for women is 170. Healthy individuals have mean COMPASS scores in the order of 10.
A rheumatologist examined all cases to assess the presence of FM following the American College of Rheumatology 1990 criteria. According to these guidelines, a person can be classified as having FM if he/she has widespread pain for more than 3 months' duration and widespread allodynia manifested by pain elicitation when applying pressure on 11 or more points on specific anatomical sites.
The presence of allodynia was also assessed with a sphygmomanometer following the previously published protocol. Blood pressure cuff is inflated at the rate of 10 mm Hg per second up to 180 mm Hg. The following question is asked to the patient: "Tell me if the cuff's pressure brings forth pain." In a previous study, pain generation during blood pressure testing was associated with the diagnosis of FM and with the FIQ. If no pain was elicited at 180–mm Hg pressure, the maneuver was classified as "negative."
Statistical Analysis
Exploratory analysis showed that numerical data had a distribution different from normal (Shapiro-Wilks normality test P > 0.05). Therefore, data are presented as median and 25th to 75th percentile and were compared among studied groups with Mann-Whitney U test. Spearman coefficients were used to correlate age and blood pressure (systolic and diastolic) with total FIQ scores and COMPASS scores. Nominal or categorical variables were tabulated to estimate its frequencies and proportions and were compared with χ or Fisher exact tests as required. Statistical significance was set at P ≤ 0.05.