Parameters of cardiac function in chronic heart failure
Determinants of cardiac performance
- Preload: ventricular filling (end-diastolic volume and pressure). Raised in heart failure (HF) by salt and water retention → congestion.
- Afterload: the wall stress the ventricle must overcome in systole (arterial pressure, systemic vascular resistance, cavity radius). Raised by vasoconstriction and dilatation.
- Contractility (inotropy): reduced in HF with reduced ejection fraction (HFrEF).
- Heart rate: cardiac output = stroke volume × heart rate; tachycardia compensates but shortens diastole and coronary filling.
Cardiac function (red) and venous return (blue) curves. Weaker contraction lowers the red curve: the heart then works at a higher filling pressure (congestion) for a lower output, and fluid retention shifts the blue curve to the right.
Image: “Starling RAP combined” by Huckfinne, Public domain, via Wikimedia Commons.
Main parameters
Methods
- Echocardiography: first-line for EF, volumes, valves, filling pressures and pulmonary pressure. Cardiac MRI: the reference for volumes, EF and scar. Radionuclide ventriculography is an alternative.
- Right heart catheterisation: right atrial, pulmonary artery and wedge pressures, cardiac output (thermodilution or Fick: CO = O₂ consumption / arteriovenous O₂ difference), mixed venous saturation (normally 65–75%, low in low output). Not routine; used in advanced HF, before transplantation, for pulmonary hypertension or unclear haemodynamics.
- N-terminal pro-B-type natriuretic peptide (NT-proBNP) in follow-up: a clear fall during treatment means a better prognosis and a rise warns of decompensation; titrating drugs to the NT-proBNP level has not improved outcomes beyond good clinical titration. Sacubitril/valsartan raises BNP, so follow NT-proBNP.