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B-type natriuretic peptide testing in a nurse-led heart failure clinic

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Heart failure has a significant impact on health and its prevalence increases with age (Cowie et al, 1997). Coronary heart disease (CHD) and hypertension are the most common causes (Cowie et al, 1999). The National Service Framework for Coronary Heart Disease identifies that people with suspected heart failure should be offered appropriate investigations to confirm the diagnosis and identify the cause (DoH, 2000). Also, those with confirmed heart failure should be offered treatment to relieve symptoms and reduce the risk of death. The National Institute for Clinical Excellence will publish guidelines this summer, which will aim to improve the management of heart failure.

Abstract

 

VOL: 99, ISSUE: 27, PAGE NO: 44

Elaine Coady, MSc, RGN, is nurse consultant in cardiology, St Thomas’ Hospital, London

 

Heart failure has a significant impact on health and its prevalence increases with age (Cowie et al, 1997). Coronary heart disease (CHD) and hypertension are the most common causes (Cowie et al, 1999). The National Service Framework for Coronary Heart Disease identifies that people with suspected heart failure should be offered appropriate investigations to confirm the diagnosis and identify the cause (DoH, 2000). Also, those with confirmed heart failure should be offered treatment to relieve symptoms and reduce the risk of death. The National Institute for Clinical Excellence will publish guidelines this summer, which will aim to improve the management of heart failure.


Difficulty with diagnosis


It is difficult to diagnose heart failure based on history and physical examination alone. Symptoms are often non-specific, and the clinical signs are not sensitive enough to make an accurate diagnosis without additional investigations (Remme et al, 2001).


Symptoms vary but commonly include breathlessness, reduced exercise tolerance, lethargy and oedema. However, all of these may be attributed to other pathologies such as respiratory disease or obesity.


Investigation for heart failure


The aims are to:


- Confirm or refute the presence of heart failure;


- Identify the aetiology;


- Exclude other conditions;


- Assess left ventricular function;


- Estimate prognosis and risk of mortality (DoH, 2000).


Investigations that can aid diagnosis include:


- 12-lead electrocardiogram (ECG) - This is a relatively simple, cheap, painless and accessible non-invasive test. It is unusual for a patient with heart failure to have a normal ECG. Specific abnormalities such as Q waves or left bundle branch block may be suggestive of previous myocardial infarction, or there may be changes that indicate left ventricular hypertrophy (thickening of the ventricle wall).


- Chest X-ray (CXR) - This may provide evidence of cardiomegaly (enlarged heart) but this is not always associated with left ventricular dysfunction. The CXR may identify the presence of pulmonary oedema or help to determine if the symptoms are due to respiratory disease.


- Echocardiogram - This is the best assessment of heart failure, as it provides valuable information about the structure and function of the heart. It can assess the degree of left ventricular dysfunction, and identify possible causes, such as disease of the heart valves.


- Other investigations - Full blood count, profile of renal function, and liver function tests.


Although the ECG is used widely in primary care, facilities for CXR and echocardiograms are usually situated in secondary care and access may be limited. This may contribute to many patients in the UK being diagnosed and treated for heart failure without proper objective evidence of cardiac dysfunction.


Natriuretic peptides


Biochemical markers have become an important additional diagnostic tool in cardiology. B-type natriuretic peptide (BNP) is a cardiac neurohormone secreted mainly from the ventricles of the heart in response to stretching, which is caused by increased volume of blood or increased pressure.


A BNP level within the normal range (<18.4 picograms per millilitre (pg/ml) is used in this study) is an indication that the patient’s symptoms are highly unlikely to be due to heart failure, and that another cause should be considered. It can therefore be used as a test to rule out heart failure (McDonagh et al, 1998). The normal range was determined locally by the biochemist.


Elevated levels suggest that the symptoms may be due to heart failure, and that further testing is required, usually by echocardiography. It is suggested that using BNP testing and the ECG, in addition to patient history and clinical findings, could form the basis of the initial assessment of patients with suspected heart failure.


Pilot study


In response to the NSF, a heart failure clinic was set up at St Thomas’ Hospital in London. A nurse consultant in cardiology was appointed; areas requiring service improvements were identified; and initial clinic objectives were outlined. The objectives were to:


- Improve the diagnosis of heart failure;


- Provide optimal patient management using evidence-based protocols;


- Manage medicine changes in a controlled environment;


- Improve continuity of care;


- Provide education and support, and promote self-management strategies.


It was hypothesised that BNP testing has the potential to improve heart failure diagnosis and could be used in a nurse-led triage heart failure clinic. It was thought it might also reduce referrals for echocardiography and assessment by a cardiologist, so promoting more efficient and appropriate use of resources.


Method


Ten local practices were identified as pilot sites for using BNP as a diagnostic test, and were visited by the nurse consultant. Referrals to the nurse-led triage heart failure clinic were invited for patients with newly suspected heart failure. The clinic was designed to be a one-stop service, with patients having all tests carried out in one visit. For the study, all patients underwent ECG, echocardiography and blood tests. CXRs were ordered, if indicated, after patient assessment. The nurse consultant assessed the patients, and recorded their medical histories and results of clinical examinations and diagnostic tests.


Ten consecutively referred patients had a venous blood sample collected to establish their BNP level. These were analysed retrospectively, so results were not known at the time of the consultation or initiation of any treatments.


Results


Four patients had BNP levels within the normal reference range used in this study (<18.4 pg/ml). The ECG was normal in three of these patients, and one patient had some minor non-significant changes. The ECG recordings demonstrated good left and right ventricular function for all four patients and they were referred back to primary care, as heart failure was unlikely to be the cause of the presenting symptoms.


The other six patients had BNP levels above the normal range (Table 1). Five patients had abnormal ECGs and confirmed left ventricular dysfunction on echocardiogram and were subsequently treated in the heart failure clinic. One patient with an elevated BNP level but normal heart function on echocardiogram was referred to the renal team for further investigation, after abnormal renal and liver function results were recorded.


Conclusion


The findings of this pilot study indicate that with appropriate diagnostic tools, nurses can identify patients who do not have heart failure. The remaining patients can then be referred for specialist assessment. Use of patient history, clinical findings, and relatively simple tests such as the ECG and BNP, may reduce both demand for echocardiography and the need for assessment by a cardiologist. This is a service model with the potential for use in primary care.
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