Cardiovascular control continues despite low pulse pressure in LVAD patients

Aug 14 2012

By Liam Davenport, MedWire Reporter

Patients implanted with continuous-flow left ventricular assist devices (LVADs) have low pulse pressure levels but are nevertheless able to maintain cardiovascular control through baroreflexes, German and US scientists have discovered.

LVADs were initially intended as a short-term bridge to cardiac transplantation in patients with end-stage systolic heart failure. However, donor organ shortage and device refinement and miniaturization have meant that the devices often remain implanted for months or years.

To examine whether continuous-flow LVADs impair baroreflex control of sympathetic nerve traffic, Jens Tank, from Hannover Medical School in Germany, and colleagues studied nine heart failure patients implanted with the devices and two age- and body mass index-matched healthy controls.

The researchers note in Hypertension that systolic brachial blood pressure was an average of 99 mmHg, while the mean finger pulse pressure was just 14.2 mmHg, with large variability between individuals. Compared with controls, LVAD patients had lower systolic blood pressure, lower pulse pressure, reduced heart rate variability in time and frequency, and reduced baroreflex-mediated heart rate control.

However, there were no significant differences between patients and controls in terms of overall blood pressure and sympathetic nerve traffic coupling. Furthermore, muscle sympathetic nerve activity (MSNA) bursts had normal morphology, were linked to the cardiac cycle, and were suppressed as blood pressure increased.

MSNA burst frequency was lower in two patients compared with controls, slightly increased in four patients, and significantly increased in two patients, while burst latency and the median burst amplitude were similar between the two groups. With head-up tilt, MSNA was increased by four bursts per minute, while increasing LVAD speed decreased MSNA by three bursts per minute. The mean sympathetic baroreflex slope was -3.75 per mmHg and -3.80% per mmHg in patients and controls, respectively.

The team writes: "Given the central role of [baroreflexes] in adjusting heart rate and vascular tone to the requirements of daily life, including standing, our findings are relevant for performance and quality of life in chronically implanted patients."

They add: "Our findings provide an impetus to revisit current concepts of human baroreflex physiology in health and disease, including arterial hypertension."

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