Hypertension as a Risk Factor in Atherosclerotic Cardiovascular Disease

Measurement of Blood Pressure in the Office

One of the most vexing barriers to improving hypertension treatment is the failure of clinicians to recognize the importance of accurate blood pressure (BP) measurement. The proper methodology for measuring BP is described in a comprehensive set of guidelines published by the American Heart Association (AHA), but these guidelines are limited to measurements performed in outpatient settings, which most often means measurement during brief office visits for other medical problems. Unfortunately, following the AHA guidelines involves attending to technical issues that are difficult to incorporate into a busy clinical practice, such as having the patient rest 5 minutes in a quiet area before measuring BP. As a consequence, in actual practice, office BP measurement is often haphazard and therefore unreliable.

Even when office BP is measured accurately, it is poor practice to base management decisions exclusively on office readings. Comparisons of traditional office-based BP measurements with the gold standard, 24-hr ambulatory BP monitoring, reveals that while ambulatory averages strongly predict vascular target organ damage and adverse cardiovascular events, the value of office readings is nugatory. On the other hand, patient self-monitored home readings compare favorably with ambulatory measurements and thus provide a good approach to clinical hypertension management. Accordingly, virtually all experts now recommend that patients with hypertension and those at high risk for future hypertension be instructed on the methodology and importance of home BP measurement.

The availability of low-cost oscillometric cuffs has facilitated patients’ acceptance of home monitoring, and the British Hypertension Society has undertaken to carefully assess instruments sold by a large number of manufacturers; their results are available on a website detailing which cuffs have met rigorous standards to guide recommendations of which cuff to recommend to patients ( http://www.bhsoc.org//index.php?cID=246 ). Although only a minority of insurers provide support for cuff purchase, given the low cost of devices and the great value of the information they can provide, all patients should be advised to obtain a monitor (with an upper arm cuff appropriate to arm dimensions) and to perform home monitoring on a regular basis.

Two subtypes of hypertension with important clinical consequences—office (or white-coat) and masked hypertension—can only be detected by comparing home to office readings. Office hypertension (high BP in the office, lower BP with home or ambulatory monitoring) does not reflect generalized hyperreactivity of BP in outpatient settings, nor is isolated office hypertension a risk factor for cardiovascular complications. The practice of attending only to office readings often leads to pharmacologic overtreatment, and patients suffer side effects such as dizziness and weakness, which can lead to falls and possibly to myocardial or cerebrovascular ischemia.

The less-well-recognized entity of masked hypertension (BP normal in the office but elevated at home) increases cardiovascular risk as much as BP uncontrolled in both office and out-of-office settings (sustained hypertension). Masked hypertension is probably much more common than generally recognized; estimates run as high as 10% of all hypertensive patients. Because it is so often unrecognized, it is certainly undertreated. As for white-coat hypertension, masked hypertension can only be detected and adequately managed with patient-determined home BP readings.

Although in most patients clinical management decisions should be based on home readings, some patients are unable or unwilling to self-record. For such patients, there are automated devices designed for office use that can make clinic readings more useful. The BpTRU, an automated oscillometric device that takes five readings at a predetermined interval with no observer present, seems to eliminate much of the white-coat effect and yields results that correlate well with patient-determined home readings and with ambulatory averages and thus with risk of cardiovascular disease. These devices are relatively inexpensive and generally do not interfere with patient flow even in busy offices. Use of such a device does not, however, obviate the need for home self-monitoring to identify masked hypertension.

Nondipping is another feature of hypertension that increases cardiovascular risk. Nondippers do not show the normal 10% or greater drop in mean arterial BP during sleep, and for equivalent daytime readings, nondippers have increased cardiovascular risk compared to dippers. Twenty-four-hour ambulatory monitoring with an automated device is the only way to detect this subtype of hypertension, but the cost of the monitoring system coupled with reluctance of insurers to pay for the procedure makes it difficult to incorporate this undoubtedly useful approach in clinical practice. Because nondipping results in an increased cardiovascular risk, identifying these hypertensive patients would improve hypertension treatment, particularly because many nocturnal nondippers have sodium-sensitive hypertension, which is responsive to dietary sodium restriction, and they might not need pharmacologic antihypertensive treatment. In addition, adjustments of the timing of pharmacologic therapy, such as bedtime dosing, can ameliorate nondipping.

Measurement of Blood Pressure in the Hospital

Although there are guidelines for measuring BP in outpatient settings, there is no standard for assessing BP in hospitalized patients. Patients who have undergone vascular and other major surgical procedures generally are older, have stiffer conduit vessels, and often have a decreased renal sodium excretory capacity that is inadequate to handle the fluid volumes commonly administered postoperatively. In addition, postoperative patients are often in pain or are suffering from anxiety and other psychosocial stress, all of which can increase BP acutely. As a consequence, hospitalized patients often manifest increased BP liability during postoperative inpatient care, and in usual clinical practice, acutely elevated BP (the BP spike) is treated aggressively.

Elevated BP is of particular concern after carotid surgery, where it is thought to contribute to hyperperfusion injury, but acute hypertension is also very common in settings where no target organ damage is evident, treatment is of unproven value, and the focus is strictly on lowering the numbers. This practice is potentially harmful, because the drugs used to lower BP, most often oral and intravenous labetalol and hydralazine and oral clonidine, can cause precipitous falls in BP, increase heart rate, and aggravate orthostatic hypotension, thereby increasing the risk of falls, a major cause of morbidity in inpatients. There is no evidence that treating acute hypertension in hospitalized patients who do not have hypertensive target organ damage is of any benefit, and it seems clear that caution should be exercised by clinicians who believe the practice to be warranted.