ECG Rhythms......... without the Blues! - 4/5

29th January, 2007

Summary

In the last edition we examined atrial fibrillation, the most common chronic ECG rhythm disturbance that we see. In this edition we will look at a number of extremely serious rhythm disturbances that may result in cardiac arrest.

CARDIAC ARREST RHYTHMS

Cardiac Arrest refers to the sudden and unexpected cessation of cardiac output. It can occur for a number of conditions that include the following:

  • Acute Myocardial Ischaemia and Acute Myocardial Infarction
  • Electrolyte Disorders e.g. hyperkalaemia (elevated serum potassium levels that can be seen in renal failure for example)
  • Profound Hypoxia
  • Electrocution
  • Cardiomyopathy
  • Multi-organ Failure / Trauma
  • Hypovolaemia
  • Tension Pneumothorax
  • Pulmonary Embolism
  • Toxin / Drug Effect

For guidelines on management of cardiac arrest refer to the European Resuscitation Council (UK) Guidelines available at www.resus.org.

VENTRICULAR TACHYCARDIA (VT)

VT is an ominous rhythm that can produce a spectrum of presentations including cardiac arrest and sudden death.

In an earlier chapter we examined ventricular ectopics. VT is essentially the presence of three or more consecutive ventricular ectopics. An ectopic focus within the ventricle begins to discharge regular impulses at rate of 150 - 200 beats per minute. These impulses spread through the ventricular myocardium rather than through the electrical conduction system as normal.

Not surprisingly the ECG appearance is one of a series of wide, regular QRS complexes.

Examine this ECG rhythm.

ECG rhythm strip showing ventricular tachycardia
Fig 1: Ventricular Tachycardia (VT)

  • The rhythm is regular
  • The heart rate is approx. 200 beats per minute
  • There are no obvious P waves (they may be present but are being swamped by the wide QRS complexes)
  • There are wide QRS complexes
  • Sometimes when the timing is just right an atrial impulse may be conducted to the ventricles giving a normal narrow QRS among the wider complexes.This is called a capture beat
  • The P:QRS ratio and P-R interval are not applicable
  • This rhythm is called ventricular tachycardia.

This example shows monomorphic VT as the complexes are the same. Polymorphic VT exists when the complexes are changing their morphology.

TORSADE DE POINTES

This is a variant of Polymorphic Ventricular Tachycardia that can occur in individuals with a prolonged QT interval and occasionally may be drug induced.

Torsade de Pointes means ‘twisting of points’. The complexes appear in a twisting pattern of varying amplitudes.

ECG rhythm strip showing Torsade de Pointes
Fig 2: Torsade de Pointes

VENTRICULAR FIBRILLATION (VF)

VF is a rapid, chaotic ventricular rhythm often referred to as electrical anarchy. There is no co-ordinated depolarisation within the ventricles resulting in loss of ventricular contraction and sudden death. Early defibrillation generally represents the only prospect for survival. Acute Myocardial Infarction is the commonest cause of VF. It is not uncommon for VT to degenerate into VF.

We often refer to fine and coarse VF. The latter is generally the initial presentation and is characterised by higher voltage, chaotic deflections on the ECG. Fine VF usually follows a period of coarse VF and is associated with a grave outlook.

What to look for on the ECG:

  • No identifiable P, QRS or T waves
  • A series of rapid, chaotic waves
  • The initial presentation is usually coarse VF but as the myocardium becomes increasingly hypoxic the amplitude of the waves reduces and fine VF develops

See if you can spot theses changes on the following ECG rhythm strip:

ECG rhythm strip showing Ventricular Fibrillation (VF)
Fig 3: Ventricular Fibrillation (VF)

VENTRICULAR STANDSTILL

Ventricular standstill refers to a situation where the sinoatrial node is discharging impulses as normal. However none of the impulses are conducted through the atrioventricular node to the ventricles resulting in cardiac arrest.

The ECG rhythm is characterized by the presence of P waves only.

What to look for on the ECG:

  • There are regular, normal looking P waves
  • Nothing else!

See if you can spot theses changes on the following ECG rhythm strip:

ECG rhythm strip showing Ventricular Fibrillation (VF)
Fig 4: Ventricular Standstill

VENTRICULAR ASYSTOLE

Asystole refers to complete cessation of electrical activity within the heart. It is usually a terminal event.

Asystole appears as an almost straight line on the ECG rhythm. Occasionally we see a bizarre complex occurring during asystole and this is referred to as Agonal Rhythm

What to look for on the ECG:

  • No identifiable waves seen
  • Just a ‘straightish’ line

Should be easy to spot this on the following ECG rhythm strip:

ECG rhythm strip showing Ventricular Fibrillation (VF)
Fig 5: Ventricular Asystole

In the next edition we will conclude this series of ECG articles with a final assessment. We will present you with a number of challenging ECG rhythm strips to analyze.

There will be an option for you to send us your diagnosis and the first all correct entry drawn will receive access to our online 12-Lead ECG workshop completely free of charge!

Please note: the competition is now closed, and we are no longer accepting entries.


Charles Bloe BSc RGN NDN ITU cert
Lead Lecturer and CEO - Charles Bloe Training Ltd

For more information on ECG Training visit www.cb-training.com