Content – Wide Complex Tachycardias

DRAFT – AWAITING FINAL AUTHORING

last authored: May 2016, Rushi Parikh

Introduction

A wide complex tachycardia is defined as a heart rate over 100 bpm, having a QRS complex >120msec. Pathological tachycardias may result directly from abnormal heart function, mediated by aberrant electrical activity in the atria, ventricles, or the electrical conducting system. Arrhythmias may spontaneously resolve, though they may also lead to increasingly chaotic rhythm of the heart and result in pulseless ventricular tachycardia and/or ventricular fibrillation. These signify cardiac arrest, and death will rapidly follow if defibrillation and other treatments are not provided.

Activating current originating from above ventricles that follows the electrical conduction system tends to activate the ventricles at the same time. Any aberrancy in the flow of the current that results in non-unified activation of the ventricles results in a wide complex.

Pathophysiology – General Concepts

main article: electrical control of the heart

There are many underlying processes that can lead to tachycardias.

courtesy of Angelito7

Ectopic Rhythms

If an area of tissue develops an intrinsic rate of firing faster than that of the SA node, ectopic (premature) beats can occur. They can occur due to high catecholamine concentrations, hypoxemia, ischemia, electrolyte disturbances, and drugs such as digitalis.

Abnormal Automaticity

Injured cardiomyocytes can acquire automaticity and spontaneously depolarize, though means not fully understood, but likely involving a slow calcium current.

Triggered Activity

Under certain conditions, action potentials can trigger abnormal depolarizations that result in extra heartbeats or rapid arrhythmias. Afterdepolarizations appear as oscillations and can be early, during repolarization, or delayed. Early afterdepolarizations are most common during conditions that prolong APs, such as long QT syndrome.

Reentry

Reentry occurs when impulses circulate around a unidirectional conduction block, recurrently depolarizing a region of cardiac tissue. Reentry around distinct anatomic pathways usually appears as monomorphic tachycardia on an ECG, while fibrillation is likely caused by multiple circulation reentry wave fronts.

courtesy of Life in the Fast Lane

There are many possible causes of wide complex tachycardias:

• Ventricular tachycardia: pacemaker rhythm originates within the ventricles
• SVT with aberrancy:
• Bundle branch blocks
• Wolf-Parkinson-White syndrome, with atrial fibrillation and an accessory pathway

Assessment

A tachycardia may represent a rapidly, life-threatening condition. Immediately assess the patient’s stability, including:

• Decreased level of consciousness
• Hypotension
• Chest pain

Do not spend undue time assessing the patient without ensuring the patient’s ABC’s (airway, breathing, and circulation) are being managed, as described under ‘basic life support‘.

Management – General Concepts

Treatment of tachyarrhythmias is meant to stabilize the patient, protect against lethal consequences, and mitigate the underlying cause(s) of the arrhythmia.

Call for immediate help, from experts as available.

If the patient is unstable, it is prudent to proceed immediately with synchronized cardioversion. If there is no pulse, defibrillation should be used instead. Assess and address the ABC’s when managing a patient with tachycardia. This can include:

• Opening the airway
• Providing supplemental oxygen, positive pressure ventilation, and/or intubation
• IV access x2 and fluid administration
• Chest compressions
• Defibrillation

If the patient is stable, further information may be obtained from the history, physical exam, and investigations.

Some clinicians use adenosine as a diagnostic and therapeutic tool, but it wise to consult a specialist for further management. If the rhythm is Afib and WPW, AV blocking agents may result in death.

Antiarrhythmics must be used with caution due to the high risk of further arrhythmic complications and death.

Ventricular Tachycardia with Pulse

Ventricular tachycardia (VT) is a run of three or more PVCs. Sustained VT lasts longer than 30 seconds, can induce syncope, and often requires termination by drugs or cardioversion.

Torsades de Pointes

Torsades de pointes is a form of ventricular tachycardia with varying amplitudes of QRS waves.

It is usually symptomatic and can result in death, but is frequently self-limiting.

Bundle Branch Blocks

Bundle branch blocks (BBB) are defects in the conduction system within either the left or right bundle branches, leading to the characteristic wide-complex QRS complex seen on ECG.  If a co-existing tachycardia occurs in a patient with a BBB, it results in a wide-complex tachycardia.

courtesy of Npatchett

After impulses travel through the AV node, they enter the bundle of His which further divides into the Right and Left bundles. The right bundle contains one fascicle, whereas the left contains two (anterior & posterior).  Classification becomes more complex if specific left bundle fascicles are independently blocked. These are termed hemi-fascicular blocks, bifascicular blocks, or trifascicular blocks depending on the locations of the conduction defect.

Resources and References