Dilated Cardiomyopathy

Background

  • 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).

Causes

Can be divided into ischaemic and non-ischaemic.

Ischaemic

  • Dilated cardiomyopathy commonly occurs following massive anterior MI due to extensive myocardial necrosis and loss of contractility.

Non-ischaemic

  • 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).
  • Alcoholism.
  • Toxins (e.g. doxorubicin).
  • Autoimmune disease.
  • Pregnancy (peripartum cardiomyopathy).

Electrocardiographic Features

  • 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

ECG Examples

Example 1

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).

 

Example 2

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.

 

Example 3

Dilated cardiomyopathy:

  • 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).

 

Example 4

Dilated cardiomyopathy:

  • Atrial fibrillation with LBBB is another ECG pattern commonly seen in DCM.

 

Related Topics

Further Reading

Author Credits

References

  • Chan TC, Brady WJ, Harrigan RA, Ornato JP, Rosen P. ECG in Emergency Medicine and Acute Care. Elsevier Mosby 2005.
  • Edhouse J, Thakur RK, Khalil JM. ABC of clinical electrocardiography. Conditions affecting the left side of the heart. BMJ. 2002 May 25;324(7348):1264-7. Review. PubMed PMID: 12028984; PubMed Central PMCID: PMC1123219 [Full Text].
  • Surawicz B, Knilans TK. Chou’s Electrocardiography in Clinical Practice. 6th Edition. Saunders Elsevier 2008.
  • Wagner, GS. Marriott’s Practical Electrocardiography (11th edition), Lippincott Williams & Wilkins 2007.
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