Investigation - Professor Richard Kirk 2023

Heart Failure
Introduction	Assessment	Investigations	Management	Myocarditis \| Fontan Failure		AHA Guidelines

Investigations

Investigations are necessary to determine the cause and to assess the degree of cardiac failure. These include a detailed family history as many causes are genetically determined. In addition a full social history is required as often treatment regimens for cardiac failure are arduous, requiring significant social and financial support.

Initial screening includes basic blood chemistry (renal, liver, endocrine function and assessment of vitamin levels), complete blood count and differential
A 12 lead ECG, and chest Xray are essential
Ambulatory ECG (Holter) monitoring should be undertaken evaluate for significant arrhythmias. Event monitors and loop recorders are other options in those at high risk. Cardiomyopathy caused by a primary arrhythmia is a treatable but under recognised cause of cardiomyopathy
NT-proBNP measurement allows discrimination between cardiac and pulmonary causes of respiratory symptoms. The normal range is accepted to be <500 pg/ml but varies with age and levels may be predictive of heart failure outcomes. Trends are very useful in guiding treatment
Echocardiography is an excellent method of assessing cardiac anatomy and function. Chamber size and shape demonstrate the adverse modelling seen in cardiac failure and are useful in assessing response to treatment. The ejection fraction gives a quantitative measure of function although subject to error and is afterload dependent. Wall thickness may give a clue to aetiology e.g. hypertrophic cardiomyopathy and may be increased in myocarditis. Doppler techniques allow estimation of valve regurgitation, pulmonary artery pressure and diastolic function
Cardiac MRI (cMRI) is increasingly used for both diagnostic and functional assessment of cardiac failure. Like echocardiography the functional assessment remains load dependent. The use of gadolinium allows an estimation of cardiac fibrosis. One of its strengths is imaging of the right ventricle. However the weaknesses are that anaesthesia is required for small children and those with certain types of metallic objects e.g. older pacemakers are incompatible with cMRI and metallic clips and stents may cause severe image artefacts
CT Imaging overcomes many of the limitations of cMRI but at the expense of radiation
Cardiac Catheterisation remains the "gold standard" for assessing hemodynamics (pulmonary vascular resistance, atrial and ventricular pressures) which are often necessary for decision making. Cardiac biopsy may be undertaken at the same time when indicated
Metabolic Exercise Testing for older patients is an excellent tool to assess functional capacity and follow response to treatment. In adults a VO2 < 14ml/kg/min is generally accepted as a threshold for cardiac listing
Six minute walk test can more readily be undertaken in younger children to assess functional capacity - the length of walk and degree of desaturation (if any) are useful but no pediatric cut-off criteria are available
Genetic abnormalities. Abnormalities in the cytoskeletal, Z disc and sarcomeric genes may all cause cardiomyopathy. Likewise assessment of disease specific mutations e.g. tafazzin in suspected Barth Syndrome and the dystrophin-encoding DMD gene in Duchenne muscular dystrophy is important when there is clinical suspicion. When a genetic abnormality is not obvious, whole genomic sequencing may be helpful. See further reading.

Additional testing may be required depending on the circumstances. These may include testing for:

Metabolic conditions including amino acids, acylcarnitine profile, ammonia, carnitine, lysosomal enzymes, pyruvate,
Mitochondrial abnormalities
Trace elements including copper, magnesium and selenium.
Inflammatory markers including troponin and creatinine kinase for myocardial damage
Infectious aetiologies including viral PCR
Autoantibodies in suspected autoimmune disease