Pathophysiology of Cardiac Failure Flashcards
Define inotropy.
The force of muscle contraction.
What factors influence inotropy ?
Influenced by Ca2+
– L-type channels
• opening facilitated by cAMP
– Na+/Ca2+ exchange
• inhibited indirectly by cardiac glycosides
What is the relation between contractility and CO ?
Increased contractility increases cardiac output independent of preload and afterload.
Give examples of classification of heart failures.
- New York Heart Association Classification of Heart Failure (NYHA): Based on patient symptoms
- Systolic vs. Diastolic Dysfunction: Based on ejection fraction (%)
- Right vs. Left Ventricular Dysfunction (long-term heart failure usually involves both sides)
Identify the different kinds of heart failures according to the New York Heart Association Classification of Heart Failure.
Class I: No limitation of physical activity. Ordinary physical activity does not cause undue fatigue, palpitation, dyspnea (shortness of breath)
Class II: Slight limitation of physical activity. Comfortable at rest. Ordinary physical activity results in fatigue, palpitation, dyspnea (shortness of breath).
Class III: Marked limitation of physical activity. Comfortable at rest. Less than ordinary activity causes fatigue, palpitation, or dyspnea.
Class IV: Unable to carry on any physical activity without discomfort. Symptoms of heart failure at rest. If any physical activity is
undertaken, discomfort increases.
Identify the different kinds of heart failures according to ejection fraction.
Systolic ventricular dysfunction:
– impaired cardiac contractility so ↓ ejection fraction (possibly no chance in EDV)
– (<40%; normal ~50-65%)
Diastolic ventricular dysfunction:
– normal ejection (i.e. normal contraction) fraction but impaired diastolic ventricular relaxation and decreased filling
– ∴↓ in SV and CO
What are possible causes of systolic ventricular dysfunction ?
Commonly results from conditions that affect:
- impaired contractility
– e.g. IHD, cardiomyopathy, transient MI - volume overload
– mitral and aortic regurgitation - pressure overload (increased afterload)
– valvular stenosis (aortic valve stenosis can lead to increased afterload, reducing CO); hypertension
All of these (systolic dysfunctions) result in ↑EDV (preload), ventricular dilation, ↑ventricular wall tension
What are possible causes of diastolic ventricular dysfunction ?
- impedance of ventricular expansion
– constrictive pericarditis (prevents heart from relaxing as much as it can do due to inflamed sac) etc. - increased wall thickness
– LV hypertrophy etc.
(change in vessel thickness changes its ability to fill + issues with getting blood supply deep in heart muscle tissue) - delayed diastolic relaxation
– aging; ischaemia - ↑heart rate
(less time to fill the heart, e.g. in angina)
Which of systolic or diastolic ventricular dysfunction is more common ?
Systolic ventricular dysfunction
Describe the consequences of R Heart Failure, explaining why they occur)
R Heart Failure → Congestion of peripheral tissues → Edema and ascites + GI tract congestion (→ Anorexia, GI distress, weight loss) + Liver Congestion (impaired liver function)
-Unable to cope with returning blood so blood accumulates in veinous side of circulation (start getting congestion in peripheral tissues)
-This can change hydrostatic P across capillaries in the veinous end (more elevated P), leading to accumulation of fluid in tissues, edema. Ascites is due to congestion of fluid within liver.
-Problems in the liver: toxic metabolites produced in the liver and can’t be excreted, causing liver damage +
liver not detoxifying molecules building up in other parts of the body
-If we change amount of blood flow in the GI system, we do not get as many nutrients from the GI system
Describe the consequences of L Heart Failure
L Heart Failure → Decreased CO (because cannot pump as much) + Pulmonary congestion
Decreased CO → Activity Intolerance + Signs of decreased tissue perfusion (cyanosis, signs of hypoxia)
Pulmonary congestion → Cough with frothy sputum + Orthopnea + Paroxysmal Nocturnal Dyspnoea
- Pulmonary congestion occurs because there is flow in but not flow out
- Forthy sputum due to change in hydrostatic P
Identify possible causes of R ventricular dysfunction.
Conditions impeding flow into the lungs
– Pulmonary hypertension
– Valve damage/stenosis/incompetence
Pumping ability of right ventricle
– Cardiomyopathy
– Infarction
Left ventricular failure (biggest cause)
Congenital heart defects
Identify possible causes of L ventricular dysfunction.
Hypertension (↑TPR)
Acute myocardial infarction
Aortic or mitral valve stenosis or regurgitation
Increase in pulmonary pressure can lead to right ventricular failure
How does the body respond to heart failure ?
In the early stages of heart failure, compensatory mechanisms (i.e. those involved in hypovolemia) maintain cardiac output (and MABP)
Longer-term, they contribute to the worsening of the condition (because falling CO cannot be distinguished by CV system as being a cause of heart failure, or a cause of loss of V, leading to the same response as against hypovolemia)
Why is it a problem that the response for hypovolemia is also used for heart failure ?
In hypovoalemia, vasoconstriction of systemic circulation to increase BP by increasing TPR. In heart failure, this means we are increasing afterload of an already failing heart. Similarly, SNS constricts veins (to increase veinous return) but this causes increasing stretch of ventricles. Finally, sodium and water retention into the system results in increased pressure to the system.