Abstract
Cardiomyopathy is a disease spectrum that alters the shape, function and conduction of cardiac muscle. Affecting 1 in 500 people it is often incurable; however, symptom control can improve life quality and expectancy.
Cardiomyopathy is a disease spectrum that alters the shape, function and conduction of cardiac muscle. Affecting 1 in 500 people it is often incurable; however, symptom control can improve life quality and expectancy.
Hypertrophic Obstructive Cardiomyopathy
Hypertrophic obstructive cardiomyopathy (HOCM) is a progressive disease, caused by a mutation in one of the nine sarcomeric genes. Its inheritance is autosomal-dominant with some heterogeneous phenotypes. The incidence is 0.2–0.5%.
Pathophysiology
Ventricular septal hypertrophy causes LVOT narrowing with thinning of the LV free wall. The narrowing of the LVOT during systole leads to increased systolic ejection velocity, creating a Venturi effect, drawing the anterior mitral valve leaflet (AMVL) toward the hypertrophied septum. Simultaneously, systolic anterior motion (SAM) brings the AMVL into contact with the septum, leading to LVOT obstruction and MR secondary to distortion of the MV in mid to late systole (Figure 14.1). Factors influencing this physiology are summarized in Table 14.1. Decreased compliance and diastolic dysfunction occur through increased muscle mass, decreased LV volume, increased myoplasmic [Ca2+] and myocardial fibrosis.
Figure 14.1 SAM of the AMVL dynamic LVOT obstruction and MR in HOCM.
Table 14.1 Factors determining LVOT obstruction in HOCM
| Factors increasing likelihood | Factors decreasing likelihood |
|---|---|
| ↓ Arterial BP | ↑ Arterial BP |
| ↓ Preload | ↑ LV volume |
| ↑ Blood flow velocity – inotropes | ↓ Blood flow velocity – β-blockers/verapamil |
| ↓ SVR | ↑ SVR |
Clinical Features
The most common presentation is sudden death in previously asymptomatic and athletic individuals. A small number of patients develop exertional symptoms similar to those of AS. Atrial and ventricular dysrhythmias are common.
Investigations
Imaging is the basis of investigation in HOCM, although genetic testing should be undertaken when there is a family history of unexplained sudden death. Common modalities include: echocardiography, cardiac catheterization and cardiac MRI.
Echocardiography characterises the septal thickness and LVOT diameter alongside real-time visualization of pathophysiology. CWD reveals a characteristic ‘shark tooth’ velocity contour that is different from AS (Figure 14.2), corresponding to velocity increases from SAM during systole.
Figure 14.2 CWD findings in AS and HOCM
Management
Medical: β-blockers are the first-line treatment. If the LVOT gradient and symptoms persist, a calcium channel antagonist of the verapamil type should be substituted. Implantation of a dual-chamber pacing device can improve symptoms. High-risk patients can be considered for a combined pacemaker and ICD.
Interventional: Septal myectomy through the AV orifice can relieve LVOT obstruction and is offered to symptomatic patients on maximal medical therapy. In a select group of patients, septal ablation by alcohol injection into LAD septal branches can yield similar results. Complications following intervention include a residual LVOT obstruction, a VSD and conduction abnormalities.
Anaesthetic Goals
Anaesthesia should avoid haemodynamic worsening of any LVOT obstruction and perioperative TOE is always indicated.
Box 14.1 Anaesthetic considerations in HOCM
- Preload
Better full than empty
- HR
Rather 60 than 80 bpm
- Rhythm
Preserve NSR
- Contractility
Maintain (most patients will tolerate mild depression as long as they are well filled)
- SVR
Maintain or slightly increase to preserve coronary perfusion
Dilated Cardiomyopathy
Dilated cardiomyopathy (DCM) is the most common form of cardiomyopathy, affecting mainly males aged 20–60 years. It causes a third of all cases of congestive heart failure, and although many cases are idiopathic, secondary causes arise due to myocardial damage from toxic, infectious or metabolic insults, which include: sickle cell disease, Duchenne muscular dystrophy, ischaemia, infection (viral, trypanosomal), toxins (ethanol, doxorubicin, cobalt, ionizing radiation), stimulants (amphetamine), thyroid disease (myxoedema), morbid obesity and pregnancy. Autosomal-dominant inheritance accounts for between 20–40% of patients.
Pathophysiology
DCM is characterized by impaired systolic and diastolic function with progressive ventricular enlargement and reduced compliance, function and increased risk of intracardiac thrombus formation due to low flow. Subsequent atrioventricular valve regurgitation worsens atrial enlargement, increasing the likelihood of AF.
Clinical Features
Patients can be asymptomatic but often develop progressive ventricular failure and declining functional status. Ventricular dysrhythmias are common, as are systemic embolic phenomena in the later stages of disease.
Investigations
DCM is usually diagnosed using echocardiography. 2D echocardiography shows dilatation of all four chambers and poor ventricular contractility. Other investigations such as MRI and cardiac catheterization are rarely of diagnostic value, although the latter may reveal coronary artery and valvular disease that is amenable to surgery.
Management
Patients are treated with standard heart failure therapy, comprising ACE inhibitors, diuretics and possibly digoxin. A pacemaker or ICD should be considered in patients with conduction abnormalities or arrhythmias. Despite medical therapy, a significant number of patients die within 3 years of the onset of symptoms. Mechanical ventricular assist devices and cardiac transplantation are of proven prognostic benefit.
Anaesthetic Goals
These are summarized in Box 14.2.
- Preload
Already high, avoid overfilling
- HR
Avoid tachycardia – impaired ventricular relaxation
- Rhythm
NSR preferred – little dependence on late diastolic filling
- Contractility
Maintain – inotropic support invariably needed
- SVR
Maintain or slight decrease – increase poorly tolerated
Restrictive Cardiomyopathy
Restrictive or obliterative cardiomyopathy is a rare cause of severe diastolic dysfunction with a high mortality – 70% of patients die within 5 years of symptom onset. Causes are divided into primary, which are often idiopathic; and secondary: to amyloidosis, sarcoidosis, haemochromatosis, carcinoid disease, glycogen-storage diseases, post-radiation and tropical endomyocardial fibrosis.
Pathophysiology
The condition is characterized by increasing ventricular stiffness and endocardial thrombosis, leading to poor ventricular compliance with rapid early diastolic filling. The myocardium is not normally thickened and there are similarities to constrictive pericarditis.
Clinical Features
Patients usually present with signs and symptoms of biventricular failure, although signs of right heart failure predominate. Chest pain and syncope are less common.
Investigations
This include echocardiography, endomyocardial biopsy, CT and cardiac MRI. The key features on echocardiography include biatrial dilatation, normal systolic function with restricted diastolic relaxation and restrictive filling patterns.
Management
The aim of management is to reduce filling pressures without reducing the CO. Standard heart failure treatment is not helpful as is reduces venous return and systemic BP. On occasion, diuretics are indicated to relieve oedema.
Anaesthetic Goals
These are summarized in Box 14.3.
Box 14.3 Anaesthetic considerations in restrictive cardiomyopathy
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