Chronic heart failure

Definition

This condition is a syndrome rather than a single pathological process. As such, it is defined by it's symptoms and signs.

Pathophysiology

Two-thirds of heart failure is caused by coronary heart disease (i.e. myocardial infarction) with the rest being caused by hypertension, arrhythmias or valvular disease. Congenital heart defects may also cause heart failure but these are much rarer. Something has to make it harder for the heart to work which, when looking at it from a physics point-of-view means a reduction in cardiac output. Remember:

Cardiac output = Stroke volume x heart rate - peripheral resistance

Anything which reduces either stroke volume, heart rate or increase in peripheral resistance (and consequently reduces cardiac output) makes the heart work harder and can when severe enough cause heart failure. There are a variety of causes which effect each criterion:

• Reduction in stroke volume
  • Myocardial infarction - by far the most common. Killing heart muscle makes the heart less efficient, reducing stroke volume.
  • Valvular disease - Regurgitation means that a great proportion of it is either going the wrong way or dropping back into the chamber it was pumped from. De facto, this reduces stroke volume.
• Reduction in heart rate
  • Arrhythmias
• Increase in peripheral resistance
  • Hypertension - a high diastolic blood pressure (pressure of blood in the aorta when the left ventricle is filling) increases peripheral resistance, forcing the heart to either reduce stroke volume or work harder (resulting in ventricular hypertrophy)

Risk Factors

Have a look at the list of causes above. You'll get the idea for risk factors.

Clinical Features

The definitive features of heart failure are breathlessness or exhaustion on less than normal exertion OR at rest. Reduced heart function and associated changes in other organ systems are also used in the definition.