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Heart failure> text from: @Medicine_in_a Minute.pdf

Filed under: Extra — anlactunay @ 7:43 AM

Heart failure
Definition: heart failure refers to the inability of the heart to produce a cardiac output sufficient to meet the body’s metabolic demands.

•• Incidence and prevalence increase with age
•• Affects 1–2% of the population in the western world

•• The most common causes of heart failure are ischaemic heart disease, valvular heart disease, cardiomyopathy and hypertension
•• Other causes include infiltrative disease, toxins, infections (e.g. Chagas disease) and drugs

Pathophysiology: the pathophysiological process that takes place in heart failure involves a complex interplay of many factors. As cardiac output begins to decline, compensatory mechanisms (both mechanical and neurohumoral in nature) are activated in an attempt to sustain adequate tissue perfusion. These may initially be beneficial, but will lead to worsening heart failure over time as their ability to compensate declines.
•• Mechanical compensatory mechanisms include Frank–Starling forces (stretch on myocardial fibres increases subsequent stroke volume)
•• Neurohumoral compensatory mechanisms include increased sympathetic nervous system stimulation and activation of the renin–angiotensin– aldosterone system

Classification of heart failure
Heart failure can be classified as follows:
1. Anatomical
>Left heart failure (LHF)
•• The left side of the heart is usually affected first
•• Poor ventricular contraction causes blood to ‘back up’ into the lungs
•• This increases the pulmonary vein hydrostatic pressure, resulting in extravasation of fluid into the interstitium. This phenomenon is known as pulmonary oedema

>Right heart failure (RHF)
•• The most common cause of right heart failure is left heart failure
•• An increase in the pressure of the pulmonary vasculature causes the right side of the heart to pump against increased resistance
•• The right heart compensates with ventricular hypertrophy, but this leads to progressive dilatation and eventual failure
•• Less commonly, isolated RHF may occur secondary to lung disease such as pulmonary hypertension or pulmonary emboli. When this happens, it is termed cor pulmonale
•• Rarer causes are related to pulmonary and tricuspid valve pathology

2. Functional
>Systolic heart failure
•• Also known as heart failure with reduced ejection fraction (HFrEF)
•• Impaired left ventricular systolic function is a key feature
•• Poor ventricular contraction leads to reduced ejection fraction

>Diastolic heart failure
•• Also known as heart failure with preserved ejection fraction (HFpEF)
•• These patients have preserved LV systolic function
•• Ventricles are unable to relax due to stiffness, resulting in inadequate filling of the heart during diastole (EF >50%)
• • Seen in restrictive cardiomyopathy and constrictive pericarditis

>Low-output heart failure
•• Compensatory mechanisms eventually fail, resulting in reduced cardiac output
•• Caused by failure of the pump (heart), increased preload or increased afterload
•• Low-output states are seen in IHD and aortic stenosis
•• Characterised by cool peripheries and weak pulses

>High-output heart failure
•• Inability of the heart to meet increased metabolic demands of body tissues despite normal or increased cardiac output
•• This is rare and is seen in thyrotoxicosis, AV fistula, beriberi (thiamine deficiency), pregnancy and severe anaemia
•• Conversely, this form is characterised by warm peripheries and normal pulses

3. Temporal
>Acute heart failure
•• Acute heart failure is a medical emergency
•• This may occur in the context of an episode of
decompensation of chronic heart failure, which is termed ‘acute-on-chronic’ heart failure
•• Decompensation in a previously stable patient with heart failure is triggered by factors such as poor compliance with medication, infection, arrhythmias and fluid overload
•• Acute heart failure can also occur de novo in a patient with no prior chronic heart failure (i.e. in ACS and malignant hypertension)

>Chronic heart failure
•• The term ‘heart failure’, when used in clinical practice, is often synonymous with patients who present with the chronic form of this condition

New York Heart Association (NYHA) classification of the extent of heart failure
NYHA class:

I Physical activity not limited, No symptoms

II Slight limitation, Mild symptoms with ordinary activity

III Marked limitation, Symptomatic with less than ordinary activity such as walking short distances (20–50 metres)

IV Symptoms present at rest (mostly bed-bound patients).

Clinical features
•• Dyspnoea
•• Orthopnoea and paroxysmal nocturnal dyspnoea
•• Other symptoms include a nocturnal cough, chest discomfort, peripheral oedema and fatigue
•• Note that individual symptoms may differ based on the aetiological cause of the heart failure and the duration of onset
•• The presence of two major, or one major and two minor, criteria in the Framingham criteria may also be used to help suggest the diagnosis of heart failure

Examination findings:
•• Signs of right heart failure: elevated JVP, hepatomegaly, ascites, significant peripheral oedema
•• Signs of left heart failure: displaced apex beat, S3, pulmonary congestion
•• Note that in clinical practice both types of heart failure often occur simultaneously, which is termed “congestive cardiac failure”.

Investigations should be undertaken in the following order.
Stepwise plan:
1 Arrange blood tests
•• FBC, U&Es, LFTs, TFTs, lipid levels and glucose

2 Assess B-type natriuretic peptide (BNP)
•• This is released in response to myocardial stretch:
–– If levels of BNP ≥100pg/ml, investigate further and arrange for specialist referral within 6 weeks
–– If levels of BNP ≥400pg/ml, refer for specialist referral and echocardiography within 2 weeks

3 Obtain chest X-ray
•• Characteristic ‘ABCDE’ features (see Fig. 1.11)

4 Arrange for echocardiogram
•• Key investigation in suspected heart failure
•• Enables assessment of ventricular function, wall motion abnormalities and valvular or structural abnormalities

5 Obtain ECG •• Useful in evaluating potential causes

6 Arrange other investigations
•• May include angiography, CT scanning and cardiac MRI

nb. BNP levels above 400pg/ml are associated with a poor prognosis. BNP levels decrease once treatment is initiated. A higher BNP level correlates with higher mortality, and a BNP level below 100pg/ml has a very high (approximately 95%) negative predictive value in excluding heart failure. NICE, SIGN and the ESC guidelines all recommend the use of BNP in the assessment of heart failure.!.

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