Live basic principles govern feasible and useful screening:
The target condition should presage an important health problem
The health impact of a particular disease depends on its incidence, the disability it causes, and its associated mortality.
Incidence and prevalence
The annual incidence of new-onset heart failure is approximately 3/1000. Heart failure and asymptomatic left ventricular dysfunction each have an estimated population prevalence of 10 to 20/1000. Morbidity
Heart failure causes greater impairment of quality of life than any other chronic medical disorder (including diabetes, arthritis, lung disease, cancer, etc), reflected in its impact on hospital services: approximately 2/1000 of the population, or 120 000 persons, in the UK are hospitalized each year for chronic heart failure. Mortality
Sixty percent to 75% of patients die within 5 years of diagnosis. In severe heart failure, half may be dead within 12 months.
Chronic heart failure thus qualifies as a major health issue, making asymptomatic left ventricular dysfunction a legitimate target for a preventive screening program.
A known natural history with a detectable latent stage
In most industrialized countries, heart failure results mainly from coronary artery disease, often following myocardial infarction. It is usually preceded by a phase of asymptomatic left ventricular dysfunction in which objective measures show depressed cardiac contractility, but no overt heart failure. This was the type of patient recruited into the Prevention arm of the Studies Of Left Ventricular Dysfunction study (SOLVD-P). Furthermore, there is evidence from SOLVD-P and a recent report from the Framingham study that other patients with left ventricular dysfunction and dilatation, but no history of myocardial infarction, also progress to symptomatic chronic heart failure.
An accepted treatment that decreases disability and/or death
The availability of a disease- and/or prognosis-modifying treatment is the ultimate validation of a screening program. Three large studies SOLVD-P, Survival And Ventricular Enlargement (SAVE), and TRAndolapril Cardiac Evaluation (TRACE) have shown that angiotensin-converting enzyme (ACE) inhibitors substantially decrease the risk of chronic heart failure in left ventricular dysfunction following myocardial infarction.
SOLVD-P suggested that this benefit is seen in left ventricular dysfunction from whatever cause. It also showed, with the SAVE study, that ACE inhibitors decrease the hospitalization rate for heart failure, by more than one-third (SOLVD-P) and by 22% (captopril arm, SAVE study). In the SAVE study, captopril also decreased mortality in patients hospitalized for chronic heart failure.
There should be a valid and acceptable test for the condition
A screening test must be simple and inexpensive. It must also be sensitive, specific, repeatable, and patient-acceptable. Echocardiography satisfies all these criteria in experienced hands. In SOLVD, it provided prognostic information on mortality similar to that from radionuclide ventriculography. The TRACE study in the related setting of postinfarction left ventricular dysfunction confirmed the prognostic value of echocardiography and its utility in selecting patients for ACE-inhibitor treatment. The usual measure in the heart failure trials was the left ventricular ejection fraction. The TRACE study employed an echocardiographic wall motion index that was found to be highly reproducible. In clinical practice, however, a visual semiquantitative assessment of the left ventricular ejection fraction is most commonly used. More recently, the plasma levels of cardiac natriuretic peptides have been considered as a potential screening test. Though their use requires further investigation, the Guidelines of the European Society of Cardiology recommend brain natriuretic peptide (BNP) as a marker of left ventricular dysfunction with high negative and moderate positive predictive power. A normal serum BNP level practically excludes clinically significant compromise of the left ventricle.
Cost-effectiveness is influenced not only by the cost of the test, but also by the prevalence, morbidity, and mortality of the condition. Related to prevalence is the ability to identify high-risk groups for screening. Myocardial infarction is a ready denominator of an at-risk group. Par-
management; mortality; morbidity; disability; prognosis; prevention; therapeutic strategy; cost-effectiveness