Following diagnosis, laboratory investigations should be undertaken in the initial assessment of a patient with incident heart failure.5,6 Investigations aim to detect common co-morbidites or treatable precipitants of acute heart failure. Baseline measurements of full blood count and renal function also guide treatment.
- full blood count (haematocrit, haemoglobin, leucocyte count and platelets)
- anaemia is common in patients with heart failure and is associated with an increased risk of mortality
- anaemia can exacerbate underlying cardiac disease and severe anaemia may even present as heart failure
- renal function and electrolytes
- almost all drugs used to treat heart failure may have an adverse impact on renal function or electrolyte balance
- renal dysfunction itself can cause heart failure
- hyponatraemia, hypochloraemia and renal impairment are all associated with an increased risk of mortality in heart failure
- liver function including serum albumin
- liver function tests may be deranged due to congestion or underlying aetiology such as haemochromatosis
- albumin should be measured to ensure that any oedema is not due to nephrotic syndrome or other hypoalbuminaemic states such as chronic liver disease
- thyroid function tests (usually thyroid-stimulating hormone)
- both hypo and hyperthyroidism are treatable precipitants of heart failure and hypothyroidism can mimic heart failure
- fasting plasma glucose
- diabetes is a risk factor for developing heart failure and is common among patients with the disease. Although treating a high blood sugar may not improve cardiovascular outcome, it remains the cornerstone of diabetic treatment
- iron studies and serum ferritin to exclude haemachromatosis
- serum and urine protein electrophoresis to exclude AL amyloidosis
- creatine kinase, particularly in younger patients, to exclude possible generalised myopathy.
All patients with suspected heart failure should have a 12-lead electrocardiogram (ECG) as part of their initial investigations. It may be diagnostic and guide future management.5,6
- Q-waves may indicate infarcted or non-viable myocardium;
- increased voltages in the left-sided leads suggest left ventricular hypertrophy, perhaps due to hypertensive or genetic cardiomyopathy
- approximately one third of patients with heart failure have atrial fibrillation at presentation which should be managed with anticoagulation and appropriate rate or rhythm control: in some patients, atrial fibrillation may be the cause of heart failure
- conduction abnormalities such as left bundle branch block or atrioventricular (AV) nodal block may require device therapy. High degrees of AV block are a treatable cause of heart failure.
In chronic heart failure, serial ECGs may detect incident AF or left bundle branch block (~10% per year) which might change management, for example with cardiac resynchronisation therapy (module 4).
A chest X-ray (CXR) is a useful investigation for the diagnosis and management of acute heart failure. It may show:5
- alveolar shadowing indicative of frank pulmonary oedema – fluffy opacities throughout the lung fields
- upper lobe blood diversion of pulmonary vasculature – as blood is diverted to the upper lobes to compensate for the ventilation-perfusion mismatch caused by pulmonary oedema
- Kerley B lines – interstitial oedema appearing as short horizontal lines in the peripheries of the lung field
- pleural effusion
- cardiomegaly – may be the only abnormality in patients with chronic heart failure.*
* Cardiothoracic ratio is an unreliable finding to suggest the presence of heart failure; poor inspiratory effort and fat pads around the heart may give misleading results.8
The most important role of a CXR in patients with chronic heart failure is to exclude other potential causes of breathlessness, and not to assess the heart failure.