Value of sublingual isosorbide dinitrate before isoproterenol tilt test for diagnosis of neurally mediated syncope

Isoprenaline versus nitroglycerine in head-up tilt test

BACKGROUND

HUTT test is used in evaluation of syncope. Isoprenaline and isosorbide dinitrate are used to increase the sensitivity of the test. These drugs act by different mechanisms. We aimed to compare the results of isoprenaline with isosorbide dinitrate.

METHODS AND RESULTS

We studied 198 subjects referred for HUTT to our institute; those above the age of 35 years were not included in our study, because isoprenaline was not used commonly above this age; thus, only 90 subjects were analyzed. We found that isosorbide dinitrate resulted in more HUTT-positive results than isoprenaline by absolute risk difference of 26%; relative risk for positive isoprenaline was 60%, confidence interval 0.38-0.93, and P value of 0.03. There was no difference in frequency of types of responses, i.e. Type 1, Type 2, and Type 3 between passive testing, isosorbide dinitrate, and isoprenaline, confidence interval 1.53-2.02, and P value 0.71. Time to get positive response was highest for passive testing followed by ISO and ISDN; the mean was 16.85±7.00min, 9.85±5.84min, and 7.00±3.35min, respectively. Statistically, ISDN versus ISO time to get positive response was not significant; P value was 0.074 and 95% confidence interval was -0.28 to 5.98.

CONCLUSIONS

Isosorbide dinitrate yields more positive HUTT than isoprenaline. The frequencies of type of responses are not different between passive testing, isosorbide dinitrate, and isoprenaline. There is no difference in time taken for positive response between isosorbide dinitrate and isoprenaline. In comparison to isosorbide dinitrate and isoprenaline, passive testing showed longest time for positive response.

Head-up tilt testing for diagnosing vasovagal syncope: a meta-analysis

BACKGROUND

A systematic evaluation focused on sensitivity and specificity of head-up tilt testing (HUT) for diagnosing vasovagal syncope has not been previously performed. We conducted a meta-analysis of studies comparing HUT outcome between patients with syncope of unknown origin and control subjects without previous syncope.

METHODS

We searched Pubmed and Embase databases for all English-only articles concerning case-control studies estimating the diagnostic yield of HUT, and selected 55 articles, published before March 2012, including 4361 patients and 1791 controls. The influence of age, test duration, tilt angle, and nitroglycerine or isoproterenol stimulation on tilt testing outcome was analyzed.

RESULTS

Head-up tilt testing demonstrated to have a good overall ability to discriminate between symptomatic patients and asymptomatic controls with an area under the summary receiver-operating characteristics curve of 0.84 and an adjusted diagnostic odds ratio of 12.15 (p<0.001). A significant inverse relationship between sensitivity and specificity of tilt testing for each study was observed (p<0.001). At multivariate analysis, advancing age and a 60° tilt angle showed a significant effect in reducing sensitivity and increasing specificity of the test. Nitroglycerine significantly raised tilt testing sensitivity by maintaining a similar specificity in comparison to isoproterenol.

CONCLUSIONS

The results from this meta-analysis show the high overall performance of HUT for diagnosing vasovagal syncope. Our findings provide useful information for evaluating clinical and instrumental parameters together with pharmacological stressors influencing HUT accuracy. This could allow the drawing of tilt testing protocols tailored on the diagnostic needs of each patient with unexplained syncope.

Blood pressure oscillations during tilt testing as a predictive marker of vasovagal syncope

AIMS

During head-up tilt (HUT) testing, a period of haemodynamic instability, marked by oscillations in blood pressure, often precedes vasovagal syncope. We hypothesized that the presence of oscillations in blood pressure during HUT testing predicts a positive diagnosis for vasovagal syncope.

METHODS AND RESULTS

The haemodynamic profiles of 42 consecutive patients non-responsive to passive HUT and glyceryl trinitrate (GTN) provocation ('non-responders') and, contemporaneously, 41 consecutive patients responsive to passive HUT and GTN provocation ('responders') were assigned oscillation-positive or oscillation-negative depending on the presence or absence of a characteristic oscillation in systolic blood pressure which varied by > or =30 mmHg (peak-to-trough). All the non-responders proceeded to an isoprenaline (Iso) challenge test. Of the 42 non-responders, 27 patients were Iso tilt-positive; all of these patients were assigned oscillation-positive. The other 15 non-responders were Iso tilt-negative; of these 9 were assigned oscillation-positive and 6 were assigned oscillation-negative. Of the 41 responder patients, 33 were assigned oscillation-positive, whereas 8 were assigned oscillation-negative. Overall, the presence of oscillations as a diagnostic predictor for vasovagal syncope had a sensitivity of 88% (positive predictive value of 87%) and a specificity of 40% (negative predictive value of 43%).

CONCLUSION

In patients non-responsive to passive HUT and GTN provocation, the presence of an oscillating systolic blood pressure varying > or =30 mmHg may still indicate a diagnosis of vasovagal syncope, possibly obviating the need for Iso testing.

Pathophysiology, diagnosis, and treatment of orthostatic hypotension and vasovagal syncope

Orthostatic hypotension (OH) occurs in 0.5% of individuals and as many as 7-17% of patients in acute care settings. Moreover, OH may be more prevalent in the elderly due to the increased use of vasoactive medications and the concomitant decrease in physiologic function, such as baroreceptor sensitivity. OH may result in the genesis of a presyncopal state or result in syncope. OH is defined as a reduction of systolic blood pressure (SBP) of at least 20 mm Hg or diastolic blood pressure (DBP) of at least 10 mm Hg within 3 minutes of standing. A review of symptoms, and measurement of supine and standing BP with appropriate clinical tests should narrow the differential diagnosis and the cause of OH. The fall in BP seen in OH results from the inability of the autonomic nervous system (ANS) to achieve adequate venous return and appropriate vasoconstriction sufficient to maintain BP. An evaluation of patients with OH should consider hypovolemia, removal of offending medications, primary autonomic disorders, secondary autonomic disorders, and vasovagal syncope, the most common cause of syncope. Although further research is necessary to rectify the disease process responsible for OH, patients suffering from this disorder can effectively be treated with a combination of nonpharmacologic treatment, pharmacologic treatment, and patient education. Agents such as fludrocortisone, midodrine, and selective serotonin reuptake inhibitors have shown promising results. Treatment for recurrent vasovagal syncope includes increased salt and water intake and various drug treatments, most of which are still under investigation.

[Sensitization of tilt-table testing for syncope of unknown etiology: which drug to use?]

OBJECTIVE

The sensitivity of tilt-table testing in the diagnosis of vasovagal syncope is between 30% and 50% only. The most common method currently used to improve the sensitivity of the test is the administration of isoproterenol i.v. However, this method is difficult to perform and time consuming. The objective of our study was to compare sublingual trinitrin administration to i.v. isoproterenol during tilt-table testing.

METHODS

We analyzed the results of 257 consecutive patients referred for tilt testing. Patients who had a negative test received either a ten minutes infusion of i.v. isoproterenol at the dose of 4 mcg/kg/min, or 0.4 mg of trinitrin given sublingually.

RESULTS

Two hundred (and) fifty-seven patients underwent tilt-table testing. In the first group (isoproterenol group), 42 patients (39%) had a spontaneous positive tilt test, compared to 45 patients (31%) in the trinitrin group (P = NS). After sensitization, 24 additional patients (22%) had a positive test in the isoproterenol group vs 55 patients (37%) in the trinitrin group (P = NS). The total number of positive tests was 66 (61%) in the isoproterenol group compared to 100 (68%) in the trinitrin group (P = NS).

CONCLUSION

Sublingual trinitrin is at least as good as IV isoproterenol during tilt-table testing. Because trinitrin is simpler to use and because its administration is much faster than isoproterenol, it should be recommended as the drug of choice to improve the sensitivity of tilt-table testing.

Diagnostic yield of external electrocardiographic loop recorders in patients with recurrent syncope and negative tilt table test

External electrocardiographic loop recording permits extended cardiac rhythm monitoring and ECG storage before and after device activation. The purpose of the study was to assess the diagnostic yield of external loop recorders in patients with more than two syncopal events within the last 6 months and a negative tilt table test. Twenty-four consecutive patients (51 +/- 14 years, male n = 9) were enrolled with 3 +/- 4 recurrent syncopal events within the last 6 months and no overt structural heart disease. The loop recorder CardioCall continuously records a two-channel ECG via skin electrodes. When activated, up to 4.5 minutes of the ECG preceding activation is stored. The time between tilt table testing and monitoring was 5 +/- 4 weeks. The average monitoring period covered 50 +/- 22 days. Recording was either unsuccessful or terminated prematurely in 5 patients. The reasons were skin irritation secondary to the electrodes in two patients, cable damage in one patient, and two patients inadvertently erased the stored data when replacing the batteries. Fourteen patients activated the loop recorder at least once. Symptoms leading to device activation were syncope (n = 1), dizziness (n = 11), feeling unwell (n = 7), palpitations (n = 5), headaches (n = 1), and chest pain (n = 1). The loop recorder documented sinus tachycardia during the syncopal event. Sinus tachycardia was also observed in 7 other patients, and atrial flutter in two patients. Eight patients had recurrent syncope with two patients experiencing syncope prior to the monitoring period, one syncope occurred in a patient who inadvertently erased the stored data, one event coincided with sinus tachycardia, and 4 (17%) patients had syncope during 15 +/- 10 months after termination of loop monitoring. The external loop recorder was not very useful for arrhythmia detection in patients with syncopal events, no overt heart disease, and a negative tilt table test because the cardiac rhythm was stored in only 1 of 8 (13%) patients with recurrent syncope. Reasons for the low diagnostic yield of external loop recorders were infrequent syncopal events after the baseline evaluation, with rare events during the limited monitoring period in particular, and premature termination or unsuccessful recording in 21% of patients.

Simplified tilt table test protocol with continuous upright position during medication administration and no hydration

Recommendations for head-up tilt testing (HUT) often include the prolonged abstaining from food and water consumption (nothing by mouth [NPO]) and intravenous fluids administration before HUT. After the baseline test, supine equilibration periods are recommended before and between each dose of medication. The aim of this study was to determine if similar results are obtainable with a simpler protocol. After 2-3 hours NPO, 1,540 HUTs were performed at 70 degrees for 30 minutes unless predetermined endpoints were reached. Then, with the patient remaining in the tilted position, isoproterenol (ISO) (1 microgram/min), titrated every 3 minutes to a maximum of 5 micrograms/min (n = 803 patients), sublingual nitroglycerin (NTG) (300-400 micrograms) (n = 143 patients), or edrophonium (EDP) (5 mg) repeated once after 3 minutes (n = 46 patients) were administered. No aspiration or other adverse effects attributable to the abbreviated fasting period were observed. ISO was well tolerated as doses were increased. Vasovagal manifestations developed in 31% of ISO tests, in 11% with EDP, and in 50% with NTG (P < 0.001). Time consumed with rehydration before and postural changes during HUTs may be avoided when ISO is administered. With NTG the response may be excessive.

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.