Haemodynamics and Heart Failure Flashcards
What is the juxtaglomerular apparatus?
A specialised structure in the kidney formed by the distal convoluted tubule and the glomerular afferent arteriole. Its main function is to regulate blood pressure and the filtration rate of the glomerulus.
Where is renal perfusion pressure sensed?
At the glomerulus
Where is sodium concentration sensed?
In fluid surrounding convoluted tubule
If renal perfusion or Na+ concentration reduction is sensed, what is released?
Renin
Inactive prorenin –> renin + active prorenin
What is diastolic dysfunction?
Known as heart failure with preserved ejection fraction (HFPEF)
What is systolic dysfunction?
Known as heart failure with reduced ejection fraction (HFREF)
Steps of heart failure
- Back pressure in LV causes raised pressure in pulmonary circulation
- Increased hydrostatic pressure forces fluid outside vascular compartment
- Interstitial space in lungs fills with fluid (Pulmonary oedema / Pleural effusions)
- Patient becomes breathless, oxygen sats drop
Does lying flat worsen or better symptoms of heart failure?
Lying flat worsens symptoms (orthopnoea)
What happens when heart failure affects the RV?
- Back-pressure transmits to venae cavae
- Internal jugular venous pressure rises
- Gravity and raised orthostatic pressures force fluid from vascular compartment to peripheral tissue
- Ankles / sacrum swell
- Hepatomegaly / ascites
What happens when LV stretch eventually exceeds physiological levels?
- Decompensation (move to descending limb of sarcomere tension curve)
- Small rises in LVEDP (i.e. fluid retention) cause large drops in sarcomere tension, i.e. LV contractility and stroke volume
- Reduces CO, further impact on ANS and RAS
Summary so far:
- Heart failure may be diastolic, systolic or both
- Reduced cardiac output detected by baroreceptors, JGA etc.
- Sympathetic and RAAS activation to compensate
- Chronic overactivation of both is pathological
What is a key value calculated on an echocardiogram when assessing heart failure?
Left Ventricular Ejection Factor (LVEF) for assessment of severity
≥55% is normal
45-54% is mildly impaired
36-44% is moderately impaired
≤35% is severely impaired
What is the equation for LVEF?
Stroke Volume / End Diastolic Volume
Given End Diastolic Volume is 111.45ml and End Systolic Volume is 44.76ml, find stroke volume
Stroke Volume = EDV - ESV
= 66.69ml
Given Stroke Volume is 66.69ml and End Diastolic Volume is 111.45ml, find the ejection fraction
Ejection Fraction = Stroke Volume / End Diastolic Volume
= 59.8% (normal)
Effects of diuretics?
- Limit reabsorption of fluid
- Offloads the ventricles
- Moves us back along the Starling curve
- Can maximise LV contractility
Side effects of diuretics?
Renal dysfunction
Reduces Na, K, Mg
Can induce diabetes (thiazides)
Effects of ACEi?
Block conversion of angiotensin I to angiotensin II
- Reduces effects of AgII on vasculature
- Diminishes release of aldosterone
- Can cause bradykinin accumulation cough
Effect of Angiotensin receptor blockers (ARB)?
Work on the AgII – receptor interaction
Effects of beta-blockers?
Beta-receptors are involved in myocardial and renal responses to reduced CO
Blockade of these can reduce HR
Moves back along the Bowditch curve
Allows LV more relaxation time, so better filling
Also blunts RAAS overactivation
Concomitant effects on fluid retention
Conditions where caution must be taken with beta blockers?
Asthma, low HR, heart blocks
What is Valsartan?
An ARB
What is Sacubitril?
A neprilysin inhibitor
- Enhances action of natriuretic peptides
- Promotes sodium/water excretion
Is Valsartan/Sacubitril combination good?
Combination has good evidence above ACEI/ARB
