Wide Complex Tachycardia vs SVT

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Illustration of wide complex tachycardia

Introduction

It can be quite challenging to make a correct diagnosis of wide complex tachycardia.
It’s important to make an accurate interpretation of an ECG to be able to identify the proper treatment for the disease.

During sinus rhythm, the normal QRS complex is narrow which is equivalent to less than 120 milliseconds. This is caused by the nearly simultaneous and rapid spread of the depolarizing wavefront to all parts of the ventricular endocardium and the radial spread from the endocardium to the epicardium.

A rapid propagation along the common bundle of the His-Purkinje network can help achieve the normal QRS complex. The His-Purjinke network is a collection of propagating structures involving the left and right bundle branches, the Purkinje network, and the fascicles of the left bundle branch.

A wide QRS complex is a result of a QRS complex with a duration of more than 120 milliseconds. This occurs with a slower spread of ventricular depolarization which may be caused by the relying on the slower and muscle-to-muscle spread of depolarization or any disease of the His-Purkinje network.

Wide Complex Tachycardia

Wide-complex tachycardia or WCT is a disturbance in the rhythm of the heart with a rate of more than 100 beats per minute and the duration of QRS complex at 12 milliseconds or more for adults but are relative for younger patients depending on their age.

WCT can be linked with the following diseases which bring about WCT:

  • Myocardial infarction or ischemia
  • Hypoxia
  • Atrial fibrillation with aberrancy or Paroxysmal supraventricular tachycardia (PSVT)
  • Abnormalities in the electrolytes such as magnesium, potassium, and pH changes
  • Toxication from medications like antiarrhythmics and tricyclic antidepressants

These are the following symptoms of WCT that an affected individual manifests:

  • Chest pain or ischemic
  • Decreased level of consciousness or syncope
  • Hypotension, shock, or poor perfusion
  • Shortness of breath or acute heart failure

WCT can either be regular or irregular. Regular WCT can be classified as ventricle tachycardia or supraventricular tachycardia with aberration. Both conditions can be treated with electrocardioversion or adenosine. Adenosine is used as treatment if the rhythm is confidentially recognized as supraventricular.

The treatment of the disease focuses on improving an individual’s hemodynamic status and trying to address factors that can cause the disease.

Supraventricular Tachycardia

Supraventricular Tachycardia or SVT is an abnormally rapid rhythm of the heart that is brought about by an improper or abnormal electrical activity in the atria or the upper portion of the heart.

Connection between WCT and SVT

Ventricular Tachycardia and Supraventricular Tachycardia are part of the differential diagnosis of Wide Complex Tachycardia. Wide Complex Tachycardia can either be Ventricular Tachycardia or Supraventricular Tachycardia with aberrancy. Aberrancy, also known as an aberration or aberrant condition, is a term that is used to describe electrical impulses’ abnormal conduction through the heart. It takes time to transmit the conducted signals of SVT through the myocardium so as a consequence, SVT produces a wide QRS complex in an ECG.

Differential Diagnosis of Wide Complex Tachycardia

The common problem when seeing a wide QRS complex tachycardia on the electrocardiogram or ECG is the identification of the abnormal rhythm. The clinician needs to decide whether the rhythm of the heart is of a supraventricular origin with aberrancy or whether it is of ventricular origin.

The width of the QRS complex for both VT and aberrancy is different from one patient to another.

Electrographic Clues

Irregularity: The rhythm for both VT and SVT can both be regular in the presentation. VT usually has a regular presentation while SVT usually has an irregular presentation. If SVT is caused by a re-entry, the SVT’s presentation becomes regular.

QRS width: A QRS complex of 14 milliseconds or more favors VT. BBB and aberrant rhythms rarely achieve that degree of width.

Electrical axis: SVT with aberration produces a left or right axis deviation. In VT, the axis is usually in the extreme right quadrant.

QRS concordance in precordial leads: VT displays leads that are either positive or negative complex. SVT with aberration exhibits a combination of inverted and upright complexes.

Heart tones: A varying intensity of the heart tones indicates AV dissociation which points to VT. The intensity of the heart tones does not vary in SVT.

General Guidelines for Diagnosing WCT

  1. Any WCT should be assumed to be VT unless proven otherwise. VT is the default diagnosis for WCT or a wide QRS complex.
  2. Any QRS complex diagnosis that is not typical for left or right bundle branch block strongly favors the diagnosis of VT.
  3. A wider QRS complex favors VT.
  4. During WCT, a northwest frontal axis suggests VT.
  5. WCT is more likely to be VT when the QRS complex is more notched, fractionated, or splintered during WCT.
  6. It will help the compare the QRS complex to a previous ECG in sinus rhythm. Identical QRS in sinus rhythm points to SVT with aberration.
  7. SVT can be confirmed when WCT suddenly turns into a narrow complex tachycardia with an acceleration of the heart rate.
  8. The presence of capture beats or fusion beats is an evidence of VA dissociation which is a sign of VT. A single dissociated P wave at the first signs of tachycardia during ECG is enough evidence to prove that it is VT.