Programmed atrial pacing for orthostatic hypotension

Bionic epidural stimulation restores arterial pressure regulation during orthostasis

A bionic baroreflex system (BBS) is a computer-assisted intelligent feedback system to control arterial pressure (AP) for the treatment of baroreflex failure. To apply this system clinically, an appropriate efferent neural (sympathetic vasomotor) interface has to be explored. We examined whether the spinal cord is a candidate site for such interface. In six anesthetized and baroreflex-deafferentiated cats, a multielectrode catheter was inserted into the epidural space to deliver epidural spinal cord stimulation (ESCS). Stepwise changes in ESCS rate revealed a linear correlation between ESCS rate and AP for ESCS rates of 2 pulses/s and above (r2, 0.876-0.979; slope, 14.3 +/- 5.8 mmHg.pulses(-1).s; pressure axis intercept, 35.7 +/- 25.9 mmHg). Random changes in ESCS rate with a white noise sequence revealed dynamic transfer function of peripheral effectors. The transfer function resembled a second-order, low-pass filter with a lag time (gain, 16.7 +/- 8.3 mmHg.pulses(-1).s; natural frequency, 0.022 +/- 0.007 Hz; damping coefficient, 2.40 +/- 1.07; lag time, 1.06 +/- 0.41 s). On the basis of the transfer function, we designed an artificial vasomotor center to attenuate hypotension. We evaluated the performance of the BBS against hypotension induced by 60 degrees head-up tilt. In the cats with baroreflex failure, head-up tilt dropped AP by 37 +/- 5 mmHg in 5 s and 59 +/- 11 mmHg in 30 s. BBS with optimized feedback parameters attenuated hypotension to 21 +/- 2 mmHg in 5 s (P < 0.05) and 8 +/- 4 mmHg in 30 s (P < 0.05). These results indicate that ESCS-mediated BBS prevents orthostatic hypotension. Because epidural stimulation is a clinically feasible procedure, this BBS can be applied clinically to combat hypotension associated with various pathophysiologies.

Successful treatment of severe orthostatic hypotension with cardiac tachypacing in dual chamber pacemakers

Orthostatic hypotension is an evolving and disabling disease usually observed in elderly patients with dramatic consequences on morbidity, mortality, and impairing the quality of life. We studied the effects of the pacing rate and AV interval on the blood pressure drop in the upright position in two patients with previously implanted pacemakers for sinus node dysfunction. Although the AV interval did not affect the blood pressure drop in the upright position, tachypacing at 100 paces/min improved it dramatically and prevented syncope. Cardiac tachypacing is a useful therapeutic option in severe refractory orthostatic hypotensive patients, especially those with chronotropic incompetence.

Treatment of malignant primary vasodepressive neurocardiogenic syncope with a rate responsive pacemaker driven by heart contractility

In a 41-year-old man suffering from frequent syncope, the tilt test reproducibly induced a primary vasodepressive neurocardiogenic syncope. Pharmacotherapy either failed to prevent the syncope induced at the tilt test or was poorly tolerated. In the minutes preceding the syncope, a dramatic increase in heart contractility was sensed by a microaccelerometer located at the tip of a right ventricular pacing electrode. When the tilt test was repeated with the pacemaker programmed in the DDDR mode, high rate dual chamber pacing occurred during the tilt phase and prevented the syncope. Three months after implantation, the patient remains totally symptom free.

Should a VVIR Pacemaker Increase the Heart Rate with Standing?

To assess the usefulness of incorporating a posture sensor into a ventricular inhibited rate modulated pacemaker, the hemodynamic effects of increasing the ventricular pacing rate with standing were studied in 15 pacemaker dependent patients aged 55 +/- 3.5 years. In a randomized cross-over design, the pacing rate remained at 70 or was increased to 100 beats/min immediately prior to standing. Blood pressure was monitored continuously and forearm blood flow was measured by venous occlusion plethysmography. There was no difference in supine blood pressure (117 +/- 4/63 +/- 3 compared to 118 +/- 5/64 +/- 4 mmHg) or forearm blood flow (2.88 +/- 0.36 vs 2.94 +/- 0.32 mL/100 mL/min) before the 70 or 100 pacing rate intervention. With standing, blood pressure fell to an equivalent degree at the two pacing rates (fall in mean blood pressure at 70 beats/min 6 +/- 4 and at 100 beats/min 8 +/- 2 mmHg, P = 0.7). After 1 minute of standing differences in blood pressure were similar, but after 2.5 minutes of standing the increase in mean blood pressure was less at 70 than at 100 beats/min (increase from control 28 +/- 2 compared to 36 +/- 3 mmHg, P = 0.002). Forearm blood flow decreased after standing for 1 and 2.5 minutes but there was no difference between the 70 and 100 pacing rates (fall in forearm blood flow at 2.5 minutes 0.50 +/- 0.24 and 0.59 +/- 0.25 mL/100 mL/cm2).(ABSTRACT TRUNCATED AT 250 WORDS)

Orthostatic hypotension: therapeutic alternatives for geriatric patients

Symptomatic orthostatic hypotension is a serious problem in the elderly because it can precipitate falls and fractures, myocardial infarctions, and strokes. Several disorders may cause symptomatic orthostatic hypotension including age-related changes in physiology, disorders of the autonomic nervous system, drugs, and a decrease in circulating blood volume. Orthostatic hypotension is defined as a fall in systolic pressure of at least 20-30 mm Hg and a fall in diastolic pressure of at least 10-15 mm Hg upon rising, with symptoms of cerebral ischemia. Management includes a search for reversible causes as well as nonpharmacologic and pharmacologic therapies. No single agent has been universally successful in relieving the symptoms of orthostatic hypotension. Trials of single agents or combinations of agents are needed to identify the most appropriate therapy for individual patients.