7.3 Cardiomyopathy Flashcards
A 36-year-old man is scheduled for elective nasal polypectomy.
The nurse in the preoperative assessment unit tells you that he has got a murmur
loudest at the sternal edge.
He had been informed of the murmur many years ago, when he fainted as a teenager on a hot summer day.
But he had remained asymptomatic and never been investigated.
How would you proceed?
It is wise to attend preassessment to see the patient.
- History—
about the fainting incident,
family history, and
current medical
history focusing on cardiac symptoms
of exertional dyspnoea, fatigue, angina, syncope
- Examination—
thorough systemic examination with
particular emphasis to
the cardiovascular system - Investigations—to assess the cause and pathology of the murmur
What investigations would you do?
The various investigations that might be necessary are 12 lead ECG, ECHo,
cardiac catheterisation, and radionuclide imaging to study associated coronary
artery disease.
MRI is increasingly used nowadays.
comment on the ecG shown
- Voltage criteria for left ventricular hypertrophy (LVH).
- Deep narrow Q waves < 40 ms wide in the lateral leads I, aVL, and V4–6
These two features are suggestive of LVH with an old lateral infarct.
- In an asymptomatic young patient,
this ECG raises suspicion of an alternate pathology and
not ‘prior lateral infarction’.
An ECG that meets LVH criteria in a young person with
suspected syncope, think “Hypertrophic Cardiomyopathy”!
What is the differential diagnosis?
- Aortic valve stenosis
- Mitral valve insufficiency
- Hypertrophic Cardiomyopathy (HCM)
- Glycogen storage diseases—Pompe’s disease
- Lysosomal storage disease—Fabry’s diseas
What are the echo findings of HcM?
I
Asymmetric septal hypertrophy and nondilated left ventricular cavity.
Echo confirms the size of the heart,
the pattern of ventricular hypertrophy,
contractile function of heart,
and severity of outflow tract obstruction.
Two-dimensional (2-D) echocardiography is
diagnostic for hypertrophic cardiomyopathy.
The common findings are
abnormal systolic anterior leaflet motion (SAM) of the mitral valve,
LV hypertrophy,
left atrial enlargement,
small ventricular chamber size,
septal hypertrophy,
mitral valve prolapse, and
mitral regurgitation.
A narrowing of the LV outflow tract occurs in many patients with
HCM, contributing to the creation of a pressure gradient.
Cardiac magnetic resonance imaging (MRI) is very useful in the diagnosis and
assessment of hypertrophic cardiomyopathy, particularly apical hypertrophy.
What is HcM?
HCM is an intrinsic myocardial disorder characterised by unexplained LVH
that is inappropriate and often asymmetrical and
occurs in the absence of an obvious hypertrophic stimulus
such as pressure overload or storage/infiltrative disease.
It is classified as the most common purely genetic cardiovascular
disease causing sudden death in young people with a
prevalence of 1:500 and affecting twice as many men as women.
What is primary and secondary cardiomyopathy?
Primary cardiomyopathy (intrinsic) is due to weakness
in the myocardium due to intrinsic cause.
- Genetic:
HCM, arrythmogenic right ventricular cardiomyopathy (ARVC) - Mixed:
dilated and restrictive cardiomyopathy - Acquired:
peripartum cardiomyopathy
Secondary cardiomyopathy (extrinsic) is
where the primary pathology is outside the myocardium.
secondary cardiomyopathy examples
- Ischemia: coronary artery disease
- Metabolic: amyloidosis, haemochromatosis
- Endocrine: diabetic, acromegaly
- Toxicity: alcohol, chemotherapy
- Inflammatory: viral myocarditis
- Neuromuscular: muscular dystrophy
What is the inheritance of HCM?
It is a genetic disorder that is typically inherited
in an autosomal dominant fashion with
variable penetrance and variable expressivity.
It is attributed to mutations of genes that encode
for sarcomere proteins such as myosin heavy
chain, actin, and tropomyosin.
What is the clinical presentation?
- Can be asymptomatic in many patients and
diagnosed during a routine
examination or investigation. - Dizziness, fainting, chest pain, and shortness of breath after exercise,
blackouts, fatigue, and palpitations are present when symptomatic. - Signs include
hypotension, low-volume pulse, left ventricular heave,
ejection systolic murmur, and a mitral regurgitation murmur. - Dysrhythmias and heart failure can present in some patients.
- Sudden collapse and death.
The major risk factors for sudden cardiac death are
- Family history of sudden death
- Extreme hypertrophy of the left ventricular wall (> 30 mm)
- Unexplained syncope
- Nonsustained ventricular tachycardia
Explain the pathophysiology.
The pathophysiology involves these interrelated processes.
- Ventricular hypertrophy with poor ventricular compliance and diastolic
dysfunction characterised by impaired left ventricular filling with subsequent
raised LV filling pressures. - Hypertrophy of septum with left ventricular outflow tract (LVOT) obstruction
in 20% of cases. - Mitral regurgitation due to anterior motion of the mitral valve in systole.
- Familial hypertrophy occurs due to defects in sarcomeric proteins.
This leads to myofibril disarray and fibrosis.
This can be pro-arrhythmogenic and leads to
ventricular arrhythmias. - Myocardial ischaemia (see below).
What is the mechanism leading to ischaemia?
Decreased supply
* Abnormally small partially obliterated intramural
coronary arteries as a result of hypertrophy.
- Inadequate number of capillaries for the degree of LV mass.
- Diastolic dysfunction leads to an increase in
end-diastolic pressure and
decrease in the coronary perfusion pressure. - Any decrease in systemic vascular resistance
can lead to a further reduction in coronary blood flow.
increased demand
* In addition, the hypertrophied muscle,
with a higher oxygen demand, makes
the ventricle prone to ischaemia.
________________________________
In summary, myocardial ischaemia is due to
septal/ventricular wall hypertrophy,
elevated diastolic pressures,
increased o2 demand.
Why do they get outflow obstruction?
HCM can be obstructive or nonobstructive.
Obstructive HCM is due to mid-systolic obstruction of flow through the LVOT.
The two main reasons for this are:
- Prominent hypertrophy of the interventricular septum
causing a dynamic LVOT in the subaortic region. - The velocity of blood in the outflow tract
draws the anterior mitral valve leaflet towards
the interventricular septum (Venturi effect),
thereby resulting in complete obstruction of the outflow tract.
Goals of Rx
The main goals of treatment include:
* Decreasing ventricular contractility
- Increasing ventricular volume
- Increasing ventricular compliance and LVOT dimensions
- Vasoconstriction
- Prevention of arrhythmias
