A 36 year old man was referred to our hospital because of palpitations and lypotimia. He experienced presyncope on several occasions in the morning while waking up and when suddenly standing up from a sitting position, but syncope never developed. When he came to our observation, his body weight was 95 kg and his height was 170 cm. Physical examination was normal with blood pressure of 140/90 mmHg.
ECG showed sinus rhythm of 95 beats/minute without any conduction abnormalities or ST-T changes. Neither chest x-ray nor echocardiographic examination revealed any cardiac abnormalities.
Hematological examination, urine analysis and thyroid function were all normal. At clinical presentation, atrio-ventricolar slow-fast node re-entry tachycardia was initially suspected. This hypothesis was dismissed by electrophysiological transesophageus study. We performed a head-up tilt test to evaluate his orthostatic intolerance. The tilt test was done in a quiet room and in a fasting state. The ECG was monitored continuously and recorded to assess cardiac rhythm. Blood pressure was continuously monitored with an arterial tonometer (Sure Sign V1 Electronics, Philips) placed on the left radial artery, calibrated against oscillometric sphygmomanometer pressure. A continuous electrocardiographic recorder (Holter monitor ELA medical SYNETEC) was also attached for rhythm verification.
After resting for 10 min in the supine position, he was positioned upright at an angle of 80 degrees on a tilt table with a footboard for weight bearing. The passive tilt test was performed for a maximum of 45min. His heart rhythm (HR) was 85 beats/min and blood pressure was 130/80 mmHg in the supine position. After 3 min of the tilting, his HR abruptly increased to 150 beats/min and he began to complain of lightheadedness and weakness, but hypotension did not develop.
At the end of the passive tilt test for 45 min, he had not experienced syncope or marked hypotension and when he was returned to the supine position, HR quickly went back to normal as it was at the beginning of the test.
To analyze the patient's sympathovagal balance during the head-up tilt testing, power spectral analysis of HR variability was performed using the ELA medical SYNETEC version 1.10 monitoring system. Spectral indices of HR variability were computed by Fast Fourier analysis for each 2-min interval with 1-min overlap during the passive tilt test. The power spectrum was calculated as high frequency (HF, 0.15-0.40 Hz), low frequency (LF, 0.05-0.15 Hz), and as the ratio of LF to HF power (LF/HF). The changes in HF and LF/HF during the tilt test are shown in Figure 1.
The LF/HF tended to fluctuate, but it reached a higher level after 25 min of tilting when the patient began to experience symptoms of orthostatic intolerance.
POTS diagnosis was made. He started therapy with atenolol 100 mg every morning. We suggested losing weight and increasing fluid intake about every three hours in the day. His symptoms of orthostatic intolerance resolved after about thirty days.