Winston-Salem, NC- Guiding antihypertensive therapy by the use of impedance cardiography gives more effective reductions in blood pressure in patients who are not controlled on initial therapy, a new study has shown [1].

Impedance cardiography uses sensors on the neck and chest to measure electrical-impedance changes, from which cardiac parameters such as stroke volume, cardiac output, and systemic vascular resistance are calculated.

The CONTROL study, published in the April 2006 issue of Hypertension, was conducted by a group led by Dr Ronald Smith (Wake Forest University School of Medicine, Winston-Salem, NC).

They explain that hypertension is a hemodynamic-related disorder—blood pressure rises as the result of increased systemic vascular resistance, cardiac output, and fluid volume, and antihypertensive agents lower blood pressure by reducing these parameters. Therefore, hemodynamic information could help tailor therapy and subsequently improve blood-pressure control. While invasive procedures for hemodynamic profiling are not warranted in outpatient clinics and noninvasive procedures such as echocardiography are costly and operator dependent, impedance cardiography is a reliable noninvasive method to measure hemodynamics in physician offices, they say.

A previous trial has shown that using impedance cardiography to guide antihypertensive therapy improved blood-pressure-control rates in resistant hypertension treated by hypertension specialists. In the current trial, Smith et al investigate its use in uncontrolled hypertensive patients in a primary-care setting.

They enrolled 164 such patients, who discontinued all antihypertensive medication and then had their blood pressure measured. They were randomized to either standard care with empiric selection of antihypertensive medications or to a hemodynamic arm that used impedance cardiography with the CardioDynamics BioZ system to guide treatment.

After three months of treatment, results showed that both systolic and diastolic blood-pressure reductions in the hemodynamic arm were greater than those in the standard-care arm. In addition, the hemodynamic arm achieved goal blood pressures more frequently.

In the impedance-cardiography group, vasodilators (angiotensin receptor blockers, ACE inhibitors, and calcium antagonists) were used more often when systemic vascular resistance was elevated than in the standard-care group. And likewise, beta blockade was less often used when cardiac index was low or normal in the impedance-cardiography group compared with the standard-care group.

Smith et al note that the fundamental difference between the two arms was that patient treatment in the hemodynamic arm was individualized and targeted at the hemodynamic abnormality associated with the elevated blood pressure. They point out that hemodynamically driven, individualized therapy was similarly effective regardless of age or existence of isolated systolic hypertension.

"The use of impedance cardiography to achieve greater BP control offers the potential for better short-term use of healthcare resources. In addition, the long-term benefits of even small levels of blood-pressure reduction are well-known. A sustained BP reduction of 4/3 mm Hg is expected to reduce stroke risk 23%, coronary heart disease events 15%, heart failure 16%, and overall mortality 14%," they comment.

In an accompanying editorial, Dr John Flack (Wayne State University School of Medicine, Detroit, MI) says these results are very encouraging [2]. "The use of hemodynamic parameters is intuitively appealing, because blood pressure, per se, represents the confluence of multiple hemodynamic parameters, such as systemic vascular resistance, cardiac output, and intravascular volume," he writes.

He says there are considerable clinical implications of this study. "By using individualized hemodynamic measures on patients at multiple visits, it was possible to improve blood-pressure control, as well as to more often normalize systemic vascular resistance and cardiac index. These favorable outcomes occurred even though the practitioners did not comply equally with all of the suggested therapeutic decisions in the study treatment algorithm. The difference in blood pressure (6/7 mm Hg lower in the cardiography-impedance group), if sustained over the long term, would also lead to significantly lower rates of cardiovascular morbidity and mortality."

This . . . will be one of several advances in the coming years that will truly usher in the era of individualized hypertension management.

Flack also believes these data have considerable relevance to actual primary-care clinical-practice sites. He points out that as the data were derived from primary-care practices, "the concern about the portability of these findings into routine clinical practice is therefore minimal.

"This study offers the practitioner a tool that provides validated, noninvasive measures that can vary even within an individual over time to assist in the selection of optimal therapeutic choices for lowering blood pressure. It is likely that impedance cardiography, along with emerging molecular genetic markers and other complementary noninvasive hemodynamic measurements, will be used in combination to optimize pharmacological blood-pressure lowering and target-organ protection while minimizing side effects and adverse events," he says.

He notes that a number of questions remain to be answered, such as whether impedance cardiography leads to more rapid control of blood pressure; whether once target levels are reached blood pressure persists at goal or lower levels more often; how will therapeutic decision making be undertaken in hypertensive patients with multiple hemodynamic abnormalities; and whether these hemodynamic markers will merit pharmacological targeting even after blood pressure has been normalized. Also, it remains to be seen how quickly practicing physicians (and third-party payers, treatment-guideline writers) accept this new technology, he adds.

"It is very encouraging to see a new, valid technology available in the practitioner's office that can be used to improve the likelihood of successful blood-pressure control by improving therapeutic decision making. This, I believe, will be one of several advances in the coming years that will truly usher in the era of individualized hypertension management," Flack concludes.