edema. Ultrasound of the lung may also be able to detect Kerley lines. Electrophysiology An electrocardiogram (ECG or EKG) may be used to identify arrhythmias, ischemic heart disease, right and left ventricular hypertrophy, and presence of conduction delay or abnormalities (e.g. left bundle branch block). Although these findings are not specific to the diagnosis of heart failure, a normal ECG virtually excludes left ventricular systolic dysfunction. Blood tests N-terminal pro-BNP (NT-proBNP) is the favoured biomarker for the diagnosis of heart failure, according to guidelines published 2018 by NICE in the UK. Brain natriuretic peptide 32 (BNP) is another biomarker commonly tested for heart failure. An elevated NT-proBNP or BNP is a specific test indicative of heart failure. Additionally, NT-proBNP or BNP can be used to differentiate between causes of dyspnea due to heart failure from other causes of dyspnea. If myocardial infarction is suspected, various cardiac markers may be used. Blood tests routinely performed include electrolytes (sodium, potassium), measures of kidney function, liver function tests, thyroid function tests, a complete blood count, and often C-reactive protein if infection is suspected. Hyponatremia (low serum sodium concentration) is common in heart failure. Vasopressin levels are usually increased, along with renin, angiotensin II, and catecholamines to compensate for reduced circulating volume due to inadequate cardiac output. This leads to increased fluid and sodium retention in the body; the rate of fluid retention is higher than the rate of sodium retention in the body, this phenomenon causes hypervolemic hyponatremia (low sodium concentration due to high body fluid retention). This phenomenon is more common in older women with low body mass. Severe hyponatremia can result in accumulation of fluid in the brain, causing cerebral edema and intracranial hemorrhage. Angiography Angiography is the X-ray imaging of blood vessels, which is done by injecting contrast agents into the bloodstream through a thin plastic tube (catheter), which is placed directly in the blood vessel. X-ray images are called angiograms. Heart failure may be the result of coronary artery disease, and its prognosis depends in part on the ability of the coronary arteries to supply blood to the myocardium (heart muscle). As a result, coronary catheterization may be used to identify possibilities for revascularisation through percutaneous coronary intervention or bypass surgery. Staging Heart failure is commonly stratified by the degree of functional impairment conferred by the severity of the heart failure, as reflected in the New York Heart Association