Swing Low Sweet Chariot

Swing low, sweet chariot
Swing low, sweet chariot
Coming for to carry me home,
— Written by Wallis Willis in the middle of the nineteenth century. Performed by Joan Baez in 1973 in France

Figure_1 is the ECG of a 24 year old female taken at 1514, and Figure_2 shows the frontal leads from this ECG.

Figure 1

Figure 2

Figure_3 shows the ECG at 1532 after the patient has been treated with intravenous verapamil.

+ Describe the main ECG findings

  • The initial ECG shows a narrow QRS complex tachycardia with a ventricular rate of about 150 beats per minute.
  • The rhythm is regular, and inverted P waves are seen immediately after the QRS complexes in Leads I, III and aVF (Figure 2).
  • A small upright P wave is just visible immediately after the the QRS complexes in Lead aVR.

The diagnosis is atrioventricular nodal reentrant tachycardia (AVNRT)

After treatment with verapamil the ECG at 1532 (Figure 3) shows sinus rhythm with a rate of about 83 beats per minute. The PR interval is 0.20 seconds.

The other feature (seen in both ECGs) is the small amplitude of the QRS complexes.

Small amplitude QRS complexes may be found in:

  • A single lead, often one of the frontal leads
  • Most but not all the frontal leads ([See R0013, a patient with hypothyroidism]1)
  • Only in the frontal leads (a common finding) or only in the precordial leads
  • Both the frontal leads and the precordial leads

The criteria for low electrocardiographic QRS voltage (LQRSV) is a zenith-to-nadir amplitude of the QRS complexes of less than 0.5 mV (5 mm) in all the frontal leads and less than 1.0 mV (10 mm) in all the precordial leads.

The ECGs in this case show LQRSV

Low QRS voltages may be a normal variant but can be associated with:

  • Cardiac disease

    • Multiple myocardial infarcts
    • Infiltrative cardiomyopathy e.g. amyloidosis
    • Myocarditis
    • Low QRS voltage in limb leads with normal QRS precordial amplitudes or LQRSV in limb leads with high QRS complexes in the precordial leads with poor R-wave progression (“Goldberger triad”) have been described in persons with dilated cardiomyopathy.
    • Heart failure: Pulmonary congestion ± peripheral oedema.
    • Pericardial disease
    • Pericardial effusion (± electrical alternans)
    • Constrictive pericarditis
    • Pneumopericardium
  • Hypothyroidism (although LQRSV is rarely found in hypothyroidism in the absence of pericardial effusion)

  • Obesity
  • Lung disorders
    • Patients with chronic obstructive lung disease may show LQRSV, particularly in the limb leads
    • Pneumothorax, particularly left sided
    • Pleural effusion, particularly left sided and in the absence of congestive heart failure

Key Points

  • Narrow complex tachycardia with visible retrograde P waves due to atrioventricular nodal reentrant (AVNRT)
  • Presence of low amplitude QRS voltages in the ECG
  • Discussion of causes of low QRS voltages in electrocardiographs

Reference: Madias JE. Low QRS voltage and its causes. Journal of Electrocardiology. 2008; 41:498–500