New approaches to hypertension management: Always reasonable but now necessary

“The sphygmomanometer would not be welcomed by the overworked and underpaid general practitioner already loaded with thermometer and stethoscope.” — Blake E: Recent British researches on arterial tension. Med Times Gaz 1895;23:29. In the late 1800s and early 1900s, most physicians practiced medicine without the availability of blood pressure (BP) measurements. Stephen Hale first measured arterial pressure in a horse in 1733, but it was not until Scipone Riva Rocci invented the BP cuff and Harvey Cushing introduced the concept in the United States that it was considered for clinical medicine.1 At that time, the concept of BP measurement was met with a large degree of skepticism.2 Physicians asked questions about BP such as: “Is it important clinically?” “Is it accurate?” “What is the best method to measure it?” and “Is its benefit worth the time and expense to obtain it?” Acceptance of BP measurement was slow over time, but measuring BP for the diagnosis and management of hypertension was even slower. In 1913, Janeway first reported the fatal complications of hypertension.3 Actuarial reports provided additional evidence in 1925 and 1940.4 As recounted by Page,5 it was not until the availability of oral medications in the 1950s and 1960s that physicians recognized the risks and actively treated high BP.6 During that time, most physicians still focused on the benefits of reducing diastolic BP because of its known benefit in reducing mortality risk in younger patients.7,8 In 1971, data from the Framingham Study provided compelling evidence of the risks of high systolic BP,9 but recognition and treatment of systolic BP was not fully embraced until additional studies were published in the 1980s.10,11 The equal importance of systolic and diastolic BP was finally asserted in the fifth report of the Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure (JNC V) in 1993.12 Today, we recognize that reduction of systolic BP is critically important in reducing the risk for target-organ damage and clinical events. It is not surprising that physicians are skeptical about new methods. Rigor is warranted when evaluating new medical technologies, but when we look back it is still surprising how slowly the measurement and treatment of high BP has evolved. Today, of course, none of us would treat patients without the routine use of BP measurements. We know much more about the pathophysiology, risks, and treatment of hypertension than ever before. Public health initiatives to increase awareness in the general population and among physicians have been widespread. Multiple classes of antihypertensive medications have been identified, and more than 100 medications are available for the treatment of high BP.13 New antihypertensive drugs continue to be introduced to the market, at an estimated development cost approaching 1 billion dollars per drug.14 However, improved BP control has remained an elusive target despite greater public and physician awareness and a large armament of antihypertensive medications with proven benefit. Data from the National Health and Nutrition Examination Survey, published in the JNC-7,15 reveals the general lack of progress of BP control rates in the United States (Fig. 1). In the year 2000, only 59% of the hypertensive population were being diagnosed and treated, with only 34% at treatment goal, equating to a 58% control rate among actively treated hypertensive patients. Thus, despite the large number of medications that have become available, both the overall and active treatment BP control rates have increased only 5% in 15 years. Hypertension management has become increasingly complex. The number of available drugs and comorbidities creates difficult management decisions, especially in the patient with long-standing disease. Many look to newer antihypertensive drugs recently released or under investigation, but suboptimal pharmacologic management with currently available medications is probably the most significant factor in our lack of treatment success.16 For most physicians, the only diagnostic tool that they rely upon to manage BP is their stethoscope for auscultation, or potentially an oscillometric-based BP device. Measurement of BP has been our focus, largely because it has been readily available, simple to perform, and reproducible. However, elevated mean arterial pressure is caused by a variety of mechanisms that ultimately exert their influence through increase cardiac output, systemic vascular resistance, or both. Elevated pulse pressure results from decreased vascular compliance or increased stroke volume. Unfortunately, cardiac output, systemic vascular resistance, and vascular compliance cannot be assessed by physical examination. Such hemodynamic information can only be obtained reliably using invasive or noninvasive measurement techniques. The use of invasive hemodynamic monitoring is not practical in the office management of hypertension, as it requires placement of catheters into the central venous circulation or the heart in a hospital setting. Recently, the noninvasive technology of impedance cardiography (ICG) has emerged as a valuable new tool for diagnostic and prognostic assessment in hypertensive patients to aid therapeutic decision making. The ICG approach provides a quick, painless, noninvasive method to determine a patient's blood flow (stroke volume and cardiac output), systemic vascular resistance, arterial compliance, and thoracic fluid levels. The applicability of hemodynamic data obtained noninvasively has gained popularity among physicians treating hypertension, including cardiologists, nephrologists, internists, and general practitioners. The series of articles presented in this issue of the American Journal of Hypertension add to the existing body of evidence supporting the use of ICG in hypertension. Ventura et al provide a comprehensive review of the rationale to consider hemodynamic factors in hypertension and the evidence supporting the use of ICG. Treister et al profile the normal variability of ICG hemodynamic parameters in stable patients, providing a basis to determine whether therapeutic interventions or disease progression have significantly altered underlying hemodynamics. Abdelhammed et al describe the hemodynamic differences between and within normotensive and hypertensive subjects. Alfie et al explore the hemodynamic mechanisms leading to elevated pulse pressure. Ramirez et al illustrate significant prognostic value of hemodynamics in hypertensive stroke patients. Bhalla et al identify the diagnostic roles of ICG compared with B-type natriuretic peptide levels in determining the presence of left ventricular dysfunction. Quale et al provide further evidence that measurements of BP alone do not constitute a complete picture of the underlying vascular state of the patient with chronic heart failure. Lastly, Sanford et al report several cases in which the use of ICG provided important therapeutic decision-making support. Altogether, the experiences gathered by these investigators provide compelling evidence for the introduction of new approaches for assessment of the hemodynamic characteristics of hypertensive stages and the applicability of these measures to the management of their therapies. Some have suggested that only evidence-based medicine17 should define the role of new therapies and diagnostic tools. Despite a number of evidenced-based strategies in cardiovascular medicine, most of what we do today in everyday practice is still normative; that is, it is driven by the clinical judgment and practice of experienced physicians. Clearly, there must be a balance of both evidence-based and normative factors when considering new technologies. Such balance requires an assessment of how well the current standard of care is achieving its desired results and whether restricting access to new technologies might prevent progress in patient care.18 It is fair to question whether any diagnostic technology, including ICG, should be held to the standard that a therapeutic agent must achieve in randomized clinical trials to obtain regulatory approvals. Diagnostic tests are truly different from therapeutic medications—if only because their value to improve outcomes is only as good as the clinician using the information. Nonetheless, and as Ventura et al describe in detail, ICG met criteria of evidence base medicine, including a randomized trial showing a 70% improvement in BP control rates in those with resistant hypertension.19 Further evidence of the value of ICG in mild-to-moderate hypertension is currently under investigation in the multicenter trial called Efficacy of Noninvasive Hemodynamic Monitoring to Target Reduction of Blood Pressure Levels (CONTROL). The CONTROL trial is being conducted in a primary care setting in uncontrolled hypertensive patients on one to three antihypertensive drugs. After randomization to either a standard-care or an ICG-guided arm, each patient discontinues medications for a 2-week washout period. These patients then undergo active treatment with office visits once per month for 3 months. Hemodynamic measurements from ICG are taken in both arms but are only provided to the physician in the ICG-guided arm. The primary endpoints of the study are the reduction in systolic and diastolic BP and the percentage of patients in each arm of the study who achieve BP control (defined as <140/90 mm Hg). Results are expected in mid-to-late 2005. Today, physicians and payors evaluating ICG are asking questions similar to those asked about BP more than 100 years ago. Similar to BP measurements and treatment of hypertension, the inability to recognize a new paradigm of using more advanced testing for hypertension management could lead to missed opportunities to improve patient care. When ICG is incorporated into hypertension assessment, it has the strong potential 1) to improve BP control rates, and 2) to profile which patients are at the highest long-term risk. Both of these outcomes would result in a more efficient use of health care resources. It is estimated that the costs of treating hypertension in 2003 will be more than 50 billion dollars, with almost 18 billion directly related to drug costs.20 It is also possible that a broader implementation of hemodynamic measures in hypertensive individuals will further the paradigm that reduction in BP levels should not be the only target toward the prevention and treatment of hypertensive cardiovascular disease. This possibility has been underscored in recently published, large clinical trials21,22 and associated commentaries.23 Hemodynamic and vascular compliance measures—the physiologic causes of high BP—may be even better targets of therapy.24 Additionally, ICG may provide a tool with which to identify those patients categorized as prehypertensive, who are at greatest risk for clinical events. Such risk assessment in this important population might allow earlier treatment that could prevent the progression to overt hypertension and other cardiovascular diseases, along with efficient use of health care resources. There continues to be a substantial need to improve our treatment of hypertension. History tells us that we are slow to adopt new tools that can have a significant impact on patient outcomes. It is time for a reappraisal of whether we are using all of the tools available to profile risk and to treat our hypertensive patients effectively. Many physicians and health care policy makers continue to hold out hope for improvement in hypertension management through better application of existing methods. Both the recent and not-so-recent past tell us that to truly advance, we must look at new methods. A new approach is not only reasonable but is now necessary, given our current lack of success and the known challenges that physicians treating hypertension will face in the future.