- Dilated cardiomyopathy (DCM) is a myocardial disease characterised by ventricular dilatation and global myocardial dysfunction (ejection fraction < 40%).
- Patients usually present with symptoms of biventricular failure, e.g. fatigue, dyspnoea, orthopnoea, ankle oedema.
- Associated with a high mortality (2-year survival = 50%) due to progressive cardiogenic shock or ventricular dysrhythmias (sudden cardiac death).
Can be divided into ischaemic and non-ischaemic.
- Dilated cardiomyopathy commonly occurs following massive anterior MI due to extensive myocardial necrosis and loss of contractility.
- Most cases are idiopathic.
- Up to 25% are familial (primarily autosomal dominant, some types are X-linked) .
A small proportion of cases may occur due to:
- Viral myocarditis (coxsackie B / adenovirus).
- Toxins (e.g. doxorubicin).
- Autoimmune disease.
- Pregnancy (peripartum cardiomyopathy).
- There are no ECG features unique to DCM, although the ECG is usually abnormal.
- The most common ECG abnormalities are those associated with atrial and ventricular hypertrophy — typically, left sided changes are seen but there may be signs of biatrial or biventricular hypertrophy.
- Interventricular conduction delays (eg. LBBB) occur due to cardiac dilatation.
- Diffuse myocardial fibrosis may lead to reduced voltage QRS complexes, particularly in the limb leads. There may be a discrepancy of QRS voltages with signs of hypertrophy in V4-6 and relatively low voltages in the limb leads.
- Abnormal Q waves are most often seen in leads V1 to V4 and may mimic the appearance of a myocardial infarction (“pseudoinfarction” pattern).
ECG abnormalities in DCM
- Left atrial enlargement -> may progress to atrial fibrillation.
- Biatrial enlargement
- Left ventricular hypertrophy or biventricular enlargement
- Left bundle branch block (RBBB can also occur).
- Left axis deviation.
- Poor R-wave progression with QS complexes in V1-4 (“pseudo-infarction” pattern).
- Frequent ventricular ectopics and ventricular bigeminy (seen with severe DCM).
- Ventricular dysrhythmias (VT / VF).
Ischaemic dilated cardiomyopathy:
- There is marked LVH (S wave in V2 > 35 mm) with dominant S waves in V1-4.
- Right axis deviation suggests associated right ventricular hypertrophy (i.e. biventricular enlargement).
- There is evidence of left atrial enlargement (deep, wide terminal portion of the P wave in V1).
- There are peaked P waves in lead II suggestive of right atrial hypertrophy (not quite 2.5mm in height).
This patient had four-chamber dilatation on echocardiography with severe congestive cardiac failure (awaiting cardiac transplantation).
Idiopathic dilated cardiomyopathy:
- There is evidence of left ventricular hypertrophy with large precordial voltages and an LV strain pattern in leads with a dominant R wave (I, II, V6).
- There is also evidence of biatrial enlargement in V1 with a peaked initial portion of the P wave (RAE) followed by a deep terminal negative portion (LAE).
- The changes of right ventricular hypertrophy are masked by left ventricular dominance; however, this patient had four-chamber dilatation on echocardiography.
- There is marked left ventricular hypertrophy with repolarisation abnormality (LV “strain” pattern) in V5-6.
- LV dilatation has produced an interventricular conduction delay mimicking LBBB — however, this is not LBBB as the morphology is not typical and there are small Q waves in V5-6 (the presence of Q waves in V6 rules out LBBB).
- There are some signs of left atrial enlargement — leftward deviation of the P wave axis (positive P waves in I and aVL, inverted in III and aVF) and prolongation of the terminal portion of the P wave in V1.
- Right axis deviation in the presence of LVH suggests the possibility of biventricular enlargement.
- The widespread downsloping ST depression may be due to LVH (= “appropriate discordance”) or digoxin effect (a commonly used mediation in congestive cardiac failure).
- Atrial fibrillation with LBBB is another ECG pattern commonly seen in DCM.
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