Cardiac Failure

Question 1

Explain the length-tension relationship of muscle fibres?

Answer 1

↑ sarcomere length

• leads to ↑ number of cross bridges and ↑ sensitivity of Ca++ of troponin
• ↑ force of contraction

Question 2

In the heart, what are the principles of the starling’s law?

Answer 2

↑ preload (EDV)

• leads to ↑ cardiac contraction
• ↑ SV and CO

Question 3

What is the Left Ventricular End Diastolic volume?

Answer 3

The volume of the heart just before it contracts influences the stroke volume

Question 4

How would you obtain LVEDV?

Answer 4

When you put a catheter in to the artery and inflate, you occlude the artery and you are now only getting venous pressure. It gives LVEDP or LA pressure.

Question 5

What is starling’s law responsible for?

Answer 5

Responsible for:
CO= venous return
Left heart output = Right heart output

Question 6

Why is starling’s law important clinically?

Answer 6

Important Clinically:
Dehydration → Low CO and BP
Fluid Overload → Oedema

Question 7

How is the right ventricular end diastolic volume measured?

Answer 7

The right ventricular end-diastolic pressure is measured by inserting a catheter via a vein across the tricuspid valve in order to measure the right atrial pressure. At the end of diastole:

Question 8

What is right atrial pressure equivalent to?

Answer 8

Atrial pressure = ventricular pressure = Jugular venous pressure

Question 9

How is the left ventricular end diastolic volume measured?

Answer 9

The left ventricular end-diastolic pressure is measured by inserting the catheter via an artery across the aortic valve and measuring the left atrial pressure. At the end of diastole:

Question 10

What is left atrial pressure equivalent to?

Answer 10

Atrial Pressure = ventricular pressure = pulmonary artery wedge pressure

Question 11

What is the pulmonary artery wedge pressure?

Answer 11

The pulmonary artery wedge pressure is the pressure when a catheter is wedged into pulmonary artery. It is also known as the pulmonary venous pressure.

Question 12

Explain the preload of LVEDV and RVEDV.

Answer 12

Preload:
Left Ventricular end Diastolic Pressure:
= Left atrial pressure 
= Pulmonary venous pressure
= Pulmonary artery wedge pressure

Right ventricular end diastolic pressure
= Right atrial pressure
= Jugular venous pressure

Question 13

What is oedema?

Answer 13

• Swelling of ankles, legs, sacrum, scrotum
• Interstitial fluid
• “Dropsy

Question 14

What are the pressures or forces across the capillary wall?

Answer 14

The forces across capillaries are known as Starling Forces (osmotic and hydrostatic):

• Fluid leaks in or out according to balance of forces.
• Tends out at arterial end
• Tends in at venous end
• Excess fluid removed by lymphatics
• Increases in VENOUS pressure causes fluid to leak out and oedema.

Question 15

What are some causes of oedema?

Answer 15

• Increased venous pressure
  
  • Heart failure
• Decreased osmotic pressure
  
  • Plasma protein loss: renal or liver failure
• Blocked lymphatics
  
  • Cancer
• Increased capillary permeability
  
  • Infection.

Question 16

What are two uses of end diastolic pressure?

Answer 16

The End Diastolic Pressure has two uses:

1. a measure of the filling of the ventricles
2. a measure of the venous pressure driving fuid out of capillaries

Question 17

What do LVEDP and RVEDP represent?

Answer 17

LVEDP = Preload: LV function 
LVEDP = LAP = PVP: Lung capillaries 

RVEDP = Preload: RV function 
RVEDP = RAP = JVP: Peripheral capillaries.

Question 18

What are some definitions of heart failure?

Answer 18

Cardiac Failure
- Cardiac Output less than Body Needs

• Usually due to ↓ cardiac output; Rarely due to ↑ body needs
• Usually systolic failure (Loss of contractility)

Question 19

What are some mechanisms of cardiac failure?

Answer 19

Cardiac Failure

• Oedema (pulmonary or systemic) is due to high VENOUS pressures not arterial pressures
• High arterial pressure (ie high afterload) puts a strain on the ventricle which may eventually lead to ventricular failure.

Mechanisms:

• Loss of myocardial muscle
  
  • Ischaemic heart disease
  • Cardiomyopathy
• Pressure overload
  
  • Aortic stenosis
  • Hypertension
• Volume overload
  
  • Valve regurgitation
  • Shunts (eg septal defects).

Question 20

What are some causes of cardiac failure?

Answer 20

Causes:

• Ischaemic heart disease: myocardial infarct
• Valvular heart disease
• Hypertensive heart disease
• Congenital heart disease
• Cardiomyopathy
• Cor pulmonale (right heart)
• Pericardial disease.

Question 21

What are some clinical features of cardiac failure?

Answer 21

Clinical Features:
Left heart failure 
- Shortness of breath 
- Fatigue 
- Tachycardia 
- Lung “creps” 

Right heart failure
- Oedema.

Question 22

What are some inappropriate adaptations in cardiac failure?

Answer 22

• Na+ & water retention
• K+ loss
• Vasoconstriction
  (↓ Cardiac output → ↓ Renal blood flow → Activation of renin-angiotensin- aldosterone system → Fluid, Na+ retention & K+ loss & Vasoconstriction.)
• Renin-angiotensin-aldosterone system
• Sympathetic nervous system
    (Sympathetic nervous system stimulated→ Increased noradrenaline → Initial ↑ contractility →Long term deleterious effects of vasoconstriction & Ventricular arrhythmias & Direct toxic effect.)

Question 23

Explain the difference in mechanisms between left and right heart failure?

Answer 23

Left Heart Failure:
Na+ & water retention  
	→ ↑ LVEDP to ↑ CO   
		→ ↑ LAP → ↑ PVP      
		→ Fluid leaks across alveolar-capillary membrane into lung interstitium &   		alveoli      
			→ Pulmonary congestion   
			→ Shortness of breath.

Right Heart Failure:
Na+ & water retention
→ ↑RVEDP → ↑RAP → ↑JVP
→ Peripheral oedema & Liver congestion

Question 24

What are some specific mechanisms for heart failure?

Answer 24

1. Global heart disease eg cardiomyopathy
2. Specific right heart disease:
   
   • RV cardiomyopathy
     - Right sided valves, Shunts
     - Pericardial disease
   • Pulmonary hypertension (arterial)
     - Lung disease: Cor Pulmonale
     - Pulmonary embolism
3. Left heart failure eg mitral stenosis
   → Pulmonary venous hypertension
   → Pulmonary congestion
   → Chronic hypoxia
   → Pulmonary vasoconstriction (via Endothelin – ETA receptor & Angiopoietin: Smooth muscle)
   → Pulmonary arterial hypertension
   → Right heart failure.

Question 25

What is diastolic heart failure?

Answer 25

• Normal systolic function
• Reduced LV compliance
  
  • Scar from infarct
  • Stiff from chronic hypertension or hypertrophy
• Increased LVEDP required to fill the LV so ↑ pulmonary venous pressure.

In Australia, 300,000 people have heart failure of some variety. There are 30,000 new cases per year with over 40,000 hospitalizations as primary diagnosis. 2% of deaths (2600 per year) are due to heart failure.

Question 26

What are the typical treatments for heart failure?

Answer 26

• Diuretics eg frusemide
• Aldosterone antagonists eg spironolactone
• Angiotensin Converting Enzyme Inhibitors (ACE Inhibitors) eg captopril, ramipril
• Angiotensin Receptor Antagonists eg irbesartan, candesartan

The main goals of treatment are to:
	Remove fluid (↓ preload) & Vasodilate (↓ afterload)

Question 27

What are some other treatments for heart failure?

Answer 27

Other treatments include:

• Digoxin (mild positive inotropic effect)
• β blockers
  
  • Protect heart from “toxic” effect of noradrenaline
• Positive inotropic drugs only helpful in short term.
• Treat underlying causes (via Coronary artery bypass; Valve replacement; Hypertension)
• Biventricular pacemaker
• Implantable defibrillator
• Cardiac Transplantation
• Assist devices & artificial heart