Chronic hypertension overview

Hypertension Main page
Overview
Causes
Classification Primary Hypertension Secondary Hypertension Hypertensive Emergency Hypertensive Urgency
Screening

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Assistant Editor-In-Chief: Taylor Palmieri

Overview

Arterial blood pressure (BP) is a measure of the force exerted by the blood on the arterial walls. It is the function of both the cardiac output (CO) and the systemic vascular resistance (SVR). The maintenance of a normal blood pressure value is crucial to ensure appropriate blood circulation throughout the cardiovascular system. Arterial BP is considered one of the most important vital signs in the clinical setting.

Hypertension (HTN) is generally defined as an elevated systolic blood pressure (SBP) ≥ 140 mmHg and/or diastolic blood pressure (DBP) ≥ 90 mmHg at each of two or more visits. However, target BP values are set at a lower threshold in specific populations, such as diabetics and subjects with significant proteinuria and other renal diseases.

Classification

In 2004, the Seventh Report of the Joint National Committee (JNC 7) classified blood pressure values into 4 categories: normal, prehypertension, stage I hypertension, and stage II hypertension. In 2007, the Task Force for the Management of Arterial Hypertension of the European Society of Hypertension (ESH) and the European Society of Cardiology (ESC) classified blood pressure into 7 categories. This classification remained unchanged in the 2013 ESH/ESC classification. The ESH/ESC classification excludes JNC 7’s pre-hypertension category, but includes 3 different grades of hypertension in contrast to JNC 7’s two-stage classification of hypertension.

Pathophysiology

Although the pathophysiology of secondary hypertension has been outlined, there is still much debate about the true pathogenesis of primary (essential) hypertension. It is now conceded that hypertension is caused by multiple genetic and environmental factors with varying roles between individuals.

Causes

The prevalence of primary hypertension is much more common than secondary hypertension, where only 5-10% of hypertension cases are diagnosed as secondary hypertension. When a full evaluation yields no clear etiology for the hypertension, the latter is thus identified as primary or essential hypertension. It is considered a chronic disease that requires lifetime treatment and management. If an underlying disease is identifiable as the cause of hypertension, the latter is called secondary hypertension. Causes of secondary hypertension include obstructive sleep apnea, hyperaldosteronism, kidney diseases, excess catecholamines, coarctation, cushing syndrome among other diseases.

Differentiating Hypertension from other Diseases

Sustained hypertension should be distinguished from benign entities such as white coat hypertension.

Epidemiology and Demographics

Hypertension is considered an epidemic worldwide. It continues to be one of the most common diseases. In October 2013, CDC data from the 2011-2012 National Health And Nutrition Examination Survey (NHANES) demonstrated that the overall age-adjusted prevalence of hypertension among U.S. adults aged 18 and older was 29.1%. Similar surveys conducted in Europe estimated the prevalence of hypertension to be 44%. The prevalence of hypertension increases among older patients and among non-Hispanic black patients, but is similar in both genders.

Risk Factors

Established risk factors for essential hypertension include increased alcohol intake (more than 2 drinks per day), increased salt intake in diet (more than 2 gm per day), obesity, and a sedentary lifestyle and lack of exercise. All these risk factor are reversible. Smoking is not a risk factor for hypertension.

Screening

The Joint National Committee seventh report (JNC 7) defines hypertension as a systolic blood pressure of over 140 mm Hg or a diastolic blood pressure greater than 90 mm Hg based upon the average of two or more properly measured readings at each of two or more visits after an initial screen.

Natural History, Complications and Prognosis

Even moderate elevation of arterial blood pressure leads to shortened life expectancy. At severely high pressures, mean arterial pressures 50% or more above average, a person can expect to live no more than just a few years unless appropriately treated.

Diagnosis

History

Thorough history-taking is crucial for the diagnosis and assessment of hypertension. Not only should history-taking be targeted to identify symptoms consistent with high blood pressure, but more importantly it should address risk factors and target organ damage. History-taking alone may be sufficient to diagnose some causes of secondary hypertension, such as drug-induced hypertension, and may guide healthcare providers towards individualized work-up and tailored management.

Blood Pressure Measurement

In daily practice, the frequently adopted technique for blood pressure measurement is the sphygmomanometer. Devices can be electronic, commonly used for better home blood pressure measurement, aneroid, or mercury, with the latter being the gold standard. Hypertension (HTN) is generally defined as an elevated systolic blood pressure (SBP) ≥ 140 mmHg and/or diastolic blood pressure (DBP) ≥ 90 mmHg at each of two or more visits. However, target blood pressure values are set at a lower threshold in specific populations, such as diabetics and subjects with significant proteinuria.

Laboratory Findings

Laboratory studies are often undertaken to identify possible causes of secondary hypertension, and seek evidence for end-organ damage to the heart itself or the eyes (retina) and kidneys. Diabetes and raised cholesterol levels being additional risk factors for the development of cardiovascular disease are also tested for as they will also require management.

Electrocardiogram

An electrocardiogram (EKG/ECG) is performed to evaluate for the presence of left ventricular hypertrophy or silent myocardial infarction.

Chest X Ray

A chest X-ray is performed to evaluate for signs of cardiac enlargement (cardiomegaly) or evidence of cardiac failure.

Treatment

Lifestyle Modification

Hypertension is the most common primary diagnosis in America. Initial treatment for hypertension generally involves lifestyle modifications (nonpharmacologic therapy), which is also critical for prevention of the disease. Modifications encouraged for hypertensive patients include moderate dietary salt restriction, maintain body weight or weight reduction in obese patients, increased intake of fruits and vegetables and low-fat dairy products, limited alcohol intake, and regular aerobic exercise. Although effective control of blood pressure can be achieved in most patients with hypertension, the majority will require 2 or more antihypertensive drugs.

Medical Therapy

There are three main classes of drugs that are used for initial monotherapy (when no specific indication requires other treatment methods): thiazide diuretics, long-acting calcium channel blockers (usually a dihydropyridine), and ACE inhibitors or angiotensin II receptor blockers. In some cases, particularly with patients having moderate to severe hypertension, single agent therapy does not control the blood pressure. Over time, patients who were initially controlled with monotherapy need to increase treatment to a combined therapy in order for continued blood pressure control. The primary determinant of the outcome is the attained blood pressure, not the specific drug(s) used. The goal of antihypertensive therapy in patients with uncomplicated combined systolic and diastolic hypertension is a blood pressure of below 140/90 mmHg.

Cost-Effectiveness of Therapy

In the ALLHAT trial, thiazide diuretics were just as effective as ACE inhibitors and calcium channel blockers and for this reason they are often used as first line therapy for hypertension.