2. Methods
2.1 Subjects
This study was approved by the Institutional Review Board of the Third Affiliated Hospital of Sun Yat-sen University, and also conformed to the principles of the Declaration of Helsinki. All subjects were informed about the experiments, and provided written consent before participation.
Seventy-six patients with unexplained syncope or presyncope were enrolled from September 2015 to September 2017. Patient clinical history and physical examination findings were recorded in detail, along with the results of laboratory tests such as complete blood count (CBC) and biochemical tests, and other examinations such as cardiac ultrasonography and electroencephalogram. The exclusion criteria included carotid sinus hypersensitive syndrome, sick sinus syndrome, pulmonary artery hypertension, hypertrophic obstructive cardiomyopathy, transient ischemic attack, epilepsy, brain infection, diabetes mellitus, atrial fibrillation, and contraindications for TET and HUTT. Two patients were excluded for sick sinus syndrome, and one patient was excluded for lack of a detailed clinical history.
For the remaining 73 patients, the Calgary Score was calculated based on 7 diagnostic questions regarding medical history, triggers, circumstances, and signs and symptoms of transient loss of consciousness [5]. The number, similarity, and triggers of each event were recorded. VVS was defined as syncope or presyncope occurring at least once in a patient with a Calgary syncope symptom scale of ≥ -2 [5].
2.2 Experimental protocol
Patients completed a tour of the facility, and were familiarize with all of the testing procedures before beginning the experimental protocol. The protocol consisted of 3 phases. Initially, all patients received a HUTT. Patients with negative HUTT received a TET the next day. Finally, patients with a negative TET received a second HUTT within 10 minutes after the TET.
The HUTT was performed using a DT-1 HUT instrument (JUCHI Pharmaceutical Technology Co., Ltd. China) in a quiet, temperature-controlled (25-28°C) cardiovascular lab. Patients fasted for at least 4 hours, and refrained from taking interfering medications for at least 5 days prior to the testing. A BHUT was performed after 10 min of supine rest, and the table was tilted to 70° (passive tilt phase). Heart rate and blood pressure were recorded every 3 min. At the time when presyncope or syncope became apparent during the tilt-back, heart rate and blood pressure were recorded immediately. If the patient did not appear to have a positive reaction after monitoring for 45 min, the tilt bed was returned to the initial level.
Then, a NHUT was further performed as previously described [6]. Heart rate and blood pressure were recorded, 400 µg of nitroglycerin was placed under the patient’s tongue, and the table was tilted to 70° within 10 s. Heart rate and blood pressure were recorded every 3 min. At the time when presyncope or syncope became apparent during tilt-back, heart rate and blood pressure were recorded immediately. If the patient did not appear to have a positive reaction after monitoring for 30 min, the tilt bed was returned to the initial position. Any symptoms of syncope, such as dizziness, nausea, feeling feverish, or visual or hearing difficulties were documented. If patients complained of visual ambiguity, partial or total blindness, or feeling faint, or they had syncope, the table was returned to the initial position immediately. The diagnostic criteria were based on the 1998 recommendations for the diagnosis of VVS using the HUTT published by China Journal of Cardiovascular Diseases editorial board [7]. Patients were classified as reflex syncope based on the Guidelines of Syncope by the European Society of Cardiology (ESC) [8].
Hemodynamic patterns were analyzed according to the modified Vasovagal Syncope International Study (VASIS) classification [9]. The classifications were: VASIS I, mixed response; VASIS IIa, cardio-inhibitory response without asystole; VASIS IIb, cardio-inhibitory response with asystole; VASIS III, vasodepressor response. The definitions of the classifications were as follows. VASIS I was defined as a decrease in heart rate > 10%, minimal heart rate > 40 bpm or < 40 bpm for < 10 s with or without asystole occurring within 3 s, and a blood pressure decrease begins before a decrease in heart rate. VASIS IIa was defined as a minimal heart rate < 40 bpm for > 10 s, asystole occurring in < 3 s, and a blood pressure decrease before a heart rate decrease. VASIS IIb was defined as asystole occurring for > 3 s, and a decrease in heart rate either coincides with, or precedes a fall in blood pressure. VASIS III was defined as a decrease in heart rate to < 10% of the maximal heart rate.
The standard TET was performed using the Bruce protocol on a T2100 treadmill exercise test system (GE, USA). Twelve-lead electrocardiograms were recorded during the test, including the warm-up period, exercise stage, and the recovery period. Blood pressure was measured throughout the test with a Tango blood pressure monitoring system (GE, USA), including the warm-up period, at the end of each stage, and every 3 min during the recovery period. Patients exercised up to the least their submaximal predicted heart rate for their age (submaximal predicted heart rate = 85% maximal predicted heart rate, with maximal predicted heart rate = 220 minus age). ST segment deviations were compared with the PQ isoelectric line, and were recorded with reference to the J-point along with 0.06 to 0.08 s after the inscription of the J-point [9]. Contraindications, termination criteria, and positive diagnostic criteria of the TET were in accordance with the 2002 ACC/AHA exercise test guidelines [10]. Contraindications included congenital heart disease, acute myocardial infarction within the past 6 months, unstable angina pectoris, cardiomyopathy, valvular disease, atrial fibrillation, left bundle branch block, and a cardiac pacemaker. The exercise test was halted if angina pectoris or a malignant arrhythmia occurred, blood pressure was ≥ 220/110 mm Hg, ECG showed depression or elevation ≥ 0.2mV in the ST segment, the heart rate reached the maximal predicted heart rate, or the patient complained of fatigue from exercising.
The diagnostic criteria for cardiovascular disease were: ST-segment depression ≥ 2 mm or an elevation of ≥ 1 mm, angina pectoris, ventricular tachycardia, exercise-induced hypotension (> -20 mm Hg drop in systolic blood pressure). If presyncope or syncope occurred, blood pressure was measured immediately. Two subjects recovered spontaneously. Twelve subjects were placed supine immediately after onset of presyncope or syncope. The symptoms were relieved within 1min to 10min, and the subjects’ heart rate and blood pressure returned to normal.
2.3 Statistic analysis
Sensitivity and specificity were calculated to evaluate the diagnostic performance of TET combined HUTT for diagnosis of VVS based on the Calgary score. Continuous data were expressed as mean value ± standard deviation, and categorical data were presented as absolute number and percentage. Differences in continuous data were analyzed by Student’s t-test, and categorical data were analyzed by Pearson’s chi-square test. Values of p < 0.05 were considered as significance. SPSS version 18 software was used for all statistical analysis.