Drugs that are Contraindicated in Hypertrophic Cardiomyopathy
Hypertrophic cardiomyopathy (HCM) is a condition in which the heart muscles enlarge and thicken to become stiff and less compliant to changes in diastolic pressures. The changes mostly affect the left ventricle, which is responsible for supplying blood to the peripheral tissues. The disease is largely genetic in etiology with associated environmental causes such as hypertension, diabetes mellitus and hyperthyroidism.
The risk of developing the disease increases with age. Hypertrophic cardiomyopathy presents with features of decompensated heart failure such as body swelling and cough due to fluid overload and difficulty in breathing among other features. Sudden cardiac arrest is also a common emergency presentation of the condition necessitating emergency care.
The disease poses various challenges in diagnosis and management such as:
- In most cases, diagnosis of the disease is delayed due to its prolonged asymptomatic period and hence the patients present with advanced disease states.
- Complexity of the various hemodynamic changes that are seen at different levels of severity of the disease.
- Indications and contraindications of various medications due to the hemodynamic changes of the disease.
Hemodynamic Changes of Hypertrophic Cardiomyopathy
In a normal heart, the chambers should relax adequately in diastole to allow for inflow of enough blood. This forms the basis of adequate contraction in systole as depicted by the frank sterling law that provides “the more the heart muscles stretch the more the force achieved in contraction”. Similarly, a smooth passage without obstruction and valve insufficiency is seen in a normal heart.
Changes experienced in hypertrophic cardiomyopathy include:
Inadequate Contraction and Relaxation: The thickened heart muscles contract and relax inadequately. Hence, there is insufficient filling of the chambers with blood during diastole and consequently insufficient pumping of blood during systole resulting in reduced cardiac output and features of heart failure in extreme cases. This is worsened by hardening of the valves that become floppy and regurgitant. This type of cardiomyopathy is known as hypertrophic non-obstructive cardiomyopathy (HNOCM)
Blood Passage Contraction: Thickening leads to contraction of the blood passages and thus causes hypertrophic obstructive cardiomyopathy (HOCM).
Low Electric Activity: The muscles poorly conduct the electrical activity of the heart and thus may lead to arrhythmias.
Pharmacological Treatment of Hypertrophic Cardiomyopathy
Given the hemodynamic changes above, the treatment should aim at lowering the pressure gradient across the ventricular outflow tracts and reducing the hearts ionotropic activity, more so in obstructive states. Thus, the drugs of choice here include drug with β-blocker activity which function by prolonging the diastolic filling time and hence reduce the heart rate and improve the obstruction.
In a case where β-blockers are not effective verapamil-type calcium channel blockers are recommended as they have been shown to improve diastolic function. Amiodarone is the only agent that has been proved to be beneficial in reducing the occurrence of arrhythmias.
Relative contraindications exist in the use of diuretics such as hydrochlorothiazide and angiotensinogen converting enzyme inhibitors (ACEIs) such as enalapril and lisinopril. These drugs are safe as long as close monitoring is done and once an obstructive lesion is documented the drugs must be discontinued.
Absolute contraindication is advocated with the use of nitrates, nifedipine type-calcium channel blockers and positive ionotropic drugs such as digitalis. These drugs have been shown to increase the cardiac output in a compromised heart, thus worsen the outflow tract obstruction and hence heart failure manifestations.
In summary, hypertrophic cardiomyopathy is a common disease that is largely genetic, but with associated environmental etiologies whose diagnosis and management can be challenging. Of utmost importance, is to document the presence or absence of an obstructive lesion and the ejection fraction at diagnosis as they form the basis of pharmacological therapy. Nitrates, ACEIs, nifedipine type-calcium channel blockers and positive inotropes are contraindicated in the treatment of this disease as the increase cardiac output and worsen the features of ventricular outflow obstruction.
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