Week 9- Failing heart 1 Flashcards
What are the three functions of the cardiovascular system?
- Delivery of substances
- Removal of substances
- Distribution (heat, hormones, cells, bioactive agents)
What are the two fundamental mechanical functions of the heart?
- Eject enough blood into the aorta in order to meet perfusion requirements
2.To receive blood from the systemic and pulmonary veins in order to provide adequate drainage of capillary beds
What is preload?
The volume of blood returning to the ventricle (ventricular enddiastolic volume)
* Affected by venous blood pressure and the rate of venous return, which are affected by venous tone and
volume of circulating blood.
What is afterload?
The tension, force or stress acting on ventricular wall myocytes
after onset of shortening.
* Affected by arterial and arteriolar vascular smooth muscle constriction or dilation
What is heart rate?
: Determined by the rate of spontaneous sinoatrial nodal discharge
* Under autonomic control
What is the frank starling law?
» Greater amount of blood in the ventricles
results in greater contractile strength of the
ventricles and therefore increase in stroke
volume.
» Due to the more cross-bridges cycling, and a
greater availability of Ca++ to initiate this
cycling.
What is the definition of heart failure?
Heart failure – pathophysiological state when it is unable to function to meet the animals requirements.
what is myocardial failure
Impaired contractility – primary (dilated cardiomyopathy) or secondary (related to causes below leading
to myocardial failure)
what are the two common causes of volume overload
- valvular insufficiency
- shunts
What are the main causes of valvular insufficiency?
- Most common cause of volume overload
- Incompetence of atrio-ventricular valves (endocardiosis, endocarditis, congenital) – allow for regurgitation to
occur - Can be primary (myxomatous valve degeneration) or secondary (ventricular hypertrophy, ischemia, obstruction)
What are the main causes of shunts?
- Septal defects
- Overloading a particular heart chamber
What does excessive afterload cause?
- Short increases in afterload helps with contractility but chronic increases will depress myocardial
contractility. - Overtime – reduced rate of ejection if afterload is always high, leads to also reduced volume of ejection.
- Pulmonary or systemic hypertension, obstruction of ventricular outflow tracts, stenosis cause increase
afterload
What does inadequate preload and diastolic dysfunction cause?
- Reduction in preload represent inability to adequately fill the heart and diastolic dysfunction represent the
inability to relax (expand the chambers) – somewhat interrelated. - Inadequate preload – pericarditis, pericardial effusion.
- Diastolic dysfunction – myocardial fibrosis, restrictive cardiomyopathy, failure of adequate ventricular
relaxation. - Increases in ventricular end diastolic pressure which exerts stress on the heart and lead to remodelling.
When would a cardiac cough most typically occur?
Typically occurs when there is pulmonary oedema and the fluid accumulates in the airway
* occurs with tachypnoea and dyspnoea
* acute onset, soft, moist, blood tinged sputum
How might an enlarged atrium cause coughing?
mechanical compression of the trachea
What are the four different types of dyspnoea?
- Acute – pulmonary oedema (cardiac or non cardiac), pneumonia, airway obstruction, pneumothorax, pulmonary embolism.
- Chronic (progressive) – right sided heart failure with ascites, pleural effusion, pericardial disease, bronchial disease, anaemia.
- At rest – mix of the above depending on severity.
- Exertional/on exercise – cardiomyopathies, heart failure, obstructive lung disease.
What is suggested when dyspnoea resolves with diuretic therapy?
left sided heart failure
What is suggested when dyspnoea resolves with bronchodilators?
Suggests respiratory disease
What is oedema/ ascites?
Pulmonary oedema
* Ascites – accumulation of fluid in the abdomen – typically seen in
dogs less common in cats (is it right or left heart failure?)
* Ascites not so obvious in horses - in horses classic oedema sites
ventrum, limbs, prepuce, throat latch and muzzle.
* In dogs sometimes decompensated heart failure can occur
without a murmur – if ascites in seen – include RHF as
differentials.
What is cyanosis associated with?
associated with decreased oxygenation and blue tinged mucous membranes
* occurs secondary to left sided heart failure
* insensitive indicator of deoxygenation and cardiac function- O2 saturation needs to be low to see changes
* some animals have pigmented/ dark mucous membranes
What is syncope?
- Loss of consciousness due to reduction of cerebral blood flow – can recur and typically brief in duration.
- Animals fall over suddenly but able to get back up fairly quick (depending on severity of impeded blood flow).
- There maybe involuntary urination and vocalisation – brief confusion on waking up
Why does syncope occur with heart failure?
In heart failure it occurs because the muscles are weak and the heart is unable to pump blood effectively
reduced pumping of blood to the brain leads to a reduced oxygen supply thus the brain shuts down momentarily
commonly associated with cardiac arrhythmia
What heart sounds should be present in all normal animals and therefore identified in auscultation?
S1 and S2
What might a change to S1 mean?
splitting of S1 can occur if mitral and tricuspid don’t close at the same time – valvular stenosis, ventricular ectopic beats.
* can also be soft due to pleural effusion, decreased cardiac output in late stage failure.
