|Home | About | Journals | Submit | Contact Us | Français|
ECG has low sensitivity so further tests are needed to detect organ damage
Arterial hypertension is an important public health challenge—it affects almost one third of the adult population in economically developed countries and is a major contributor of cardiovascular mortality and morbidity. The management of primary hypertension is based on three important principles—diagnosis, treatment, and identifying organ disease and indicators of subclinical organ damage.
In this week's BMJ, a systematic review by Pewsner and colleagues assesses the accuracy of electrocardiography in screening for left ventricular hypertrophy in people with hypertension.1 It finds that electrocardiography has a low sensitivity for detecting left ventricular hypertrophy compared with echocardiography.
Treatment aims for a target blood pressure below 140/90 mm Hg in the general population2 and below 130/80 mm Hg in patients with diabetes and renal dysfunction. A target of ≤130/80 mm Hg should also be considered in patients with cerebrovascular disease, cardiac disease, peripheral artery disease, and advanced retinopathy. Such a target is also advisable when evidence of organ damage is present, because even high-normal blood pressure values increase the risk of complications. Clinical history, clinical examination, and laboratory investigation detect a large proportion of patients who are at high risk. In these patients, intensive modification of risk factors and tight control of blood pressure is needed, but no other routine screening test is indicated because the severity of the condition is already established.
Most people with hypertension are not in the high risk categories for left ventricular hypertrophy, but doctors should search for indicators of subclinical organ damage in these patients to identify those at higher risk. For example, electrocardiography and evaluation of microalbuminaemia are recommended in all patients with hypertension. About 30% of unselected people with hypertension have microalbuminuria—one of the strongest risk markers for complications in untreated hypertension.3 4 A low ankle brachial blood pressure index, although less common, is easy to measure; it indicates advanced atherosclerosis and is also a strong risk marker for complications.5 6
Doctors can request other potentially useful tests, but these are rarely used in clinical practice as they can be expensive, time consuming, and no randomised trials have convincingly shown that they are useful and cost effective. Examples include ultrasound of the carotids7 8 or calcium score index of the coronary artery assessed by means of computed tomography, both of which can detect atherosclerosis9; or ambulatory electrocardiography, which detects patients with silent ischaemia or increased ventricular ectopic activity, both of which are associated with poor prognosis.10
The systematic review by Pewsner and colleagues1 establishes that electrocardiography cannot rule out left ventricular hypertrophy. None the less, left ventricular hypertrophy assessed by electrocardiography remains a specific sign of organ damage and a marker of increased risk, and it should prompt clinicians to implement a more aggressive course of risk management. The electrocardiographical results may also indicate atrial fibrillation and ischaemic heart disease. Unfortunately, the sensitivity and specificity of electrocardiography is low if interpreted by non-experts, and efforts should be made to arrange expert evaluation of electrocardiograms in general practice.
The review shows that absence of left ventricular hypertrophy on electrocardiography modifies the pre-test probability of left ventricular hypertrophy diagnosed on echocardiography from 33% to 31%, regardless of which electrocardiography criteria are used to detect hypertrophy. This apparently low yield raises the question of whether echocardiography should be part of a comprehensive assessment of cardiovascular risk in people with hypertension.
About 17% of the population may have increased left ventricular mass by echocardiography, in contrast to just 2-3% with electrocardiography. Left ventricular hypertrophy measured by echocardiography offers prognostic information beyond that provided by the evaluation of traditional cardiovascular risk factors, including electrocardiography.11 12 But in clinical practice it may be difficult to measure left ventricular mass in some patients because of poor image quality, an interobserver variation of 15%, and because echocardiography is not routinely recommended.2
Echocardiography is always indicated when doctors suspect cardiac dysfunction or structural abnormality on the basis of the patient's history, electrocardiographic results, and previous diagnoses. In uncomplicated hypertension, echocardiography is comparable to the tests already mentioned for diagnosing organ damage. These tests should be considered in patients otherwise at low risk of cardiovascular disease to determine the treatment target and intensity of risk modification needed. Local tradition and expertise may determine which of the recommended tests to use.
When organ damage is detected it should prompt clinicians to be more aggressive in reaching the target blood pressure and encourage their patients to be more compliant. Doctors should explain to their patients that hypertension has already harmed their organs and optimal treatment can slow down or stop progression.
The presence of left ventricular hypertrophy may also affect the choice of drug. Inhibitors of the renin-angiotensin-aldosterone system, calcium antagonists (amlodipine, felodipine), and probably aldosterone antagonists will reduce left ventricular mass more than other types of drugs.2
Competing interests: None declared.
Provenance and peer review: Commissioned; not externally peer reviewed.