essay 25 - heart failure - definition, etiology, pathogenesis, types

what is heart failure

• a complex clinical syndrome in which the heart is unable to pump sufficient blood to meet the metabolic need of the body. it results from impaired cardiac function (contractility, filling or both) and leads to inadequate tissue perfusion and/or congestion

etiology of heart failure

1. mechanical abnormalities

• pressure overload = e.g systemic hypertension

• volume overload - e.g chronic hypervolemia

• obstruction to filling = e.g mitral or tricuspid stenosis

2. myocardial damage

• primary cause = e.g cardiomyopathies, myocarditis

• secondary cause = e.g CAD, cor pulmonale

3. altered cardiac rhythm

• arrythmias = ventricular/atrial fibrillation

worsening factors for heart failure

• infections (specifically pulmonary)

• stress (physical or emotional)

• increased sodium intake

• pregnancy

• anaemia

• haemorrhage

• pulmonary embolism

pathogenesis

• heart failure develops due to inability of heart to maintain adequate cardiac output (CO = HR x SV)

1. impaired function

• decreased contractility (after MI, cardiomyopathy) → decreased stroke volume, decreased cardiac output

2. compensatory mechanisms kick in

• frank-starling law = increase preload (more filling) to try to increase output

• SNS activation = increase HR, increase contractility, vasoconstriction

• RAAS activation = angiotensin II (vasoconstriction), aldosterone (Na/water retention→ increased preload)

• ADH release = extra water retention

3. increased workload

• preload rises (volume overload) → congestion in lungs/systemic veins

• afterload rises (HTN, vasoconstriction) → heart works harder → hypertrophy

4. ventricular remodelling

• hypertrophy + fibrosis + dilation → stiffer and weaker ventricles

5. progressive failure

• compensations become maladaptive → congestion, low tissue perfusion, multi-organ dysfunction

types of heart failure by function

1. systolic heart failure

• the ventricles cannot contract strongly enough. EF <40%

• common causes = coronary artery disease, previous myocardial infarction, dilated cardiomyopathy

2. diastolic heart failure

• the ventricles cannot relax and fill properly EF >/= 50% (normal or high)

• the heart muscle becomes stuff and cannot hold enough blood

• common causes = long-standing hypertension, thickened heart muscle (hypertrophy), aging, restrictive cardiomyopathy

types of heart failures by side of heart involved

1. left sided heart failure

• the left ventricle fails

• blood backs up into the lungs → shortness of breath, difficulty breathing when lying flat, fluid in lungs (pulmonary edema)

2. right sided heart failure

• the right ventricle fails

• blood backs up into body → swelling of the lags and ankles, enlarged liver, fluid in the abdomen (ascites), distended veins in the neck

3. biventricular heart failure

• both left and right ventricles fail

• leads to a combination of congestion in the lungs and congestion in the body

heart failure by cardiac output (amount of blood pumped out of heart)

1. high output heart failure

• the heart pumps normally, but the body’s demand for more blood is abnormally high

• causes = severe anaemia, overactive thyroid gland (hyperthyroidism), large abnormal connections between arteries and veins (arteriovenous fistula)

2. low output heart failure

• the heart cannot pump enough blood due to weak contraction or excessive resistance

• this is the most common type

• causes - coronary artery disease, hypertension, valvular heart disease

heart failure by time course

1. acute heart failure

• develops suddenly, often life threatening

• causes = acute myocardial infarction, sudden rupture of a heart valve, severe abnormal rhythm of the heart (arrythmia), hypertensive crisis

2. chronic heart failure

• develops slowly and progressively

• characterised by periods of compensation (stable) and decompensation (worsening symptoms)