0722 - PV Loops and Heart Failure

Question 1

What is heart failure? What are the different forms?

Answer 1

Heart Failure - insufficient cardiac output to meet metabolic demand. Could be caused by output failure or volume retention, and only manifests itself after most compensatory mechanisms have been exhausted, and usually after a precipitating incident.

Commonly defined according to perfusion (forward - lack of perfusion, backward - increased venous pressure). Other methods are:

Cardiac Cycle - systolic (can’t contract) or diastolic (can’t relax or fill)
Cardiac Output - High Output (High demand - pregnancy, anaemia) or Low-output (low CO - ischaemic heart disease etc)
Development - Acute (infarct, infection, rupture of papillarymm), Chronic (slow with adaptation)
Anatomy - Left sided (pulmonary symptoms), Right-sided (peripheral systems)

Question 2

What is the pathophysiology of Heart Failure?

Answer 2

Backward failure activates CP reflex due to increased RA pressure (pooling). Forward failure activates AB reflex (sympathetic ++) due to lower blood pressure. CO is regained due to SY, at cost of increased RA pressure and HR - lots of internal work, poor energy efficiency - leads to more work for heart - vicious cycle.

Critical CO level ~5L/min for renal perfusion. If not met, RAA fires up, retaining Na+ at cost of RA pressure - delays HF, requiring increased contractility for therapy.

Question 3

What are the signs of backward heart failure?

Answer 3

• Increased RA pressure, distended central veins (raised JVP)
• Accumulation of fluid in venous bed: expansion of plasma volume (Na retention - low GFR) - weight gain, salt craving
• Peripheral oedema if MSF pressure raised significantly
• Increased RR due to lack of peripheral perfusion (CP reflex and respiratory control)
• Pulmonary oedema if backward failure in LV.

Question 4

What are the signs of forward heart failure?

Answer 4

• Fluid retention with low urine volume (low renal perfusion)
• HR increases (SY activation due to AB reflex)
• Shut down of unnecessary systems:
  Low grade fever (reduced skin perfusion)
  Muscle fatigue, cold extremities with pallor
  Viscera - anorexia and nausea with abdominal pain and feeling full (stasis in liver)
  Brain - fatigue, lack of concentration

Question 5

What are the pathophysiological principles underlying rational therapy for heart failure?

Answer 5

Aim is to balance need for decreasing heart energy demand with sufficient perfusion. So work to:
Increase SV via contractility, drop diastolic pressure (increase pressure difference), reduce central venous pressure, and reduce venous return (drop volume due to pooling)
Decrease afterload - reduce peripheral resistance and increase EF
Ensure appropriate electrical pacing - reduce HR if appropriate and convert to sinus or ‘sinus-like’ rhythm (steady output)
Provide ‘paradoxical’ energy-sparing treatment. Counteract body’s mechanisms to reduce load on heart - e.g. ACE inhibitors, beta blockers.

When HR goes up, diastole is shortened, less LCA perfusion.

Question 6

Is a failing heart in an energy crisis?

Answer 6

YES
Heart normally likes using FAs. In HF, metabolism is changed, lower substrate uptake, lower O2 for OxPhos, and lower ATP transfer as a result.