Cardiac Tachyarrhythmias

Classification and definitions of different tachyarrhythmias, investigations, and management - excluding atrial fibrillation!

Tachycardia

A faster heart rate than normal - usually defined as a resting HR > 100 bpm in adults.

Are all tachyarrhythmias a threat to the patient’s health?

No, this depends on the type and the cause. They can range from benign to life threatening.

Name the two broad categories that tachyarrhythmias are grouped by?

• Supraventricular tachycardia

• Ventricular Tachyarrhythmias

What is supraventricular tachycardia (SVT)?

A rapid heart rate originating from within or above the AVN. There are many different types of SVT, but they are (mostly!) all narrow complex (signalling they originate above the ventricles).

What are the two different classifications of SVTs?

• Focal Tachycardias

• Re-entry Tachycardias

What are Focal Tachycardias?

SVTs originating from a single point in the atrium or AVN. There is therefore organised atrial contraction, so a wave similar to a P wave will appear before the QRS complex.

What are the different types of focal tachycardias?

• Sinus tachycardia

• Focal atrial tachycardia

• Multifocal atrial tachycardia

• Junctional rhythms

What are Re-entry tachycardias?

SVTs where there are abnormal electrical conduction pathways through the heart where the impulse gets stuck in a loop, causing tachycardia. The P waves will be abnormal as conduction of the impulse is not very organised.

What are the re-entry tachycardias called?

• Atrial Flutter

• Atrial Fibrillation

• AV node re-entrant tachycardia (AVNRT)

• AV re-entrant tachycardia (AVRT)

What is sinus tachycardia?

A focal SVT, where the focus is the SAN. It is therefore usually regular. This is a normal response to different triggers such as:

• Exercise

• Dehydration

• Certain drugs (e.g. caffeine)

• Anxiety

• Illness (e.g. fever)

Sometimes there is no clear reason for the tachycardia, and this is labelled innapropriate.

What is focal atrial tachycardia?

A focus SVT where a different focus in the atrium takes over from the SAN, resulting in abnormal P waves.

Risk factors and conditions predisposing to focal atrial tachycardia

• No pattern in relation to sex or ancestry, and occurs in all age groups.

• Concomitant lung disease (e.g. COPD)

• Heart disease

• Previous MI

• Electrolyte imbalances

• Too much alcohol intake

• Infection

• Low oxygen levels

• Toxic effects of digoxin (a medication)

• Caffeine and other stimulants

• Catecholamine excess

• Congenital heart conditions

• Idiopathic

What is multifocal atrial tachycardia?

A focal SVT very similar to atrial tachycardia where different focuses in the atrium takes over from the SAN for each heartbeat, resulting in abnormal P waves with varying morphologies.

Risk factors and conditions predisposing to multifocal tachycardia

• Typically elderly patients with multimorbidity

• Lung disease, especially COPD (most common risk factor)

• Respiratory failure.

• Infection.

• Coronary artery disease.

• Heart failure.

• Low levels of potassium, magnesium or sodium.

• Cancer.

• Diabetes.

• Major surgery.

• Kidney failure.

• Pulmonary embolism (rare).

• Heart valve disease (rare).

What are junctional rhythms?

Focal SVTs where the AVN takes over from the SAN, so the atria and ventricles contract simultaneously.

Conditions predisposing to a junctional rhythm

Typically caused by SAN impairment, where the impulses are blocked or fall below the automaticity of the AVN. Tends to be seen more in elderly patients. Causes include:

• Medications

  • Digoxin

  • Drugs causing sinus bradycardia (e.g. beta blockers etc.)

• Structural and inflammatory causes:

  • Chest trauma

  • Heart diseases (Myocarditis, Pericarditis, IHD, previous MI etc.)

  • Iatrogenic (surgery and other treatments)

  • Other illnesses and disease (rheumatic fever, amyloidosis, Lyme disease etc.)

• Conduction system disorders (e.g. sick sinus syndrome, heart block)

• Neuromuscular conditions

• Systemic conditions (e.g. hypothyroidism, sleep apnea, hypoxia)

• Neurologic conditions (e.g. anorexia)

• Autonomic and reflex causes

• Electrolyte and metabolic disturbances (e.g. Hyperkalemia)

What is an atrial flutter?

A re-entry SVT where there is a large re-entry circuit (macro re-entry) around the atrium which triggers the AVN every time it goes around. The circuit is fixed, so the rate of atrial contraction is regular.

Typical vs atypical atrial flutter

• Typical atrial flutters run anti-clockwise around the right atrium and across the cavotricuspid valve isthmus. This produces the sawtooth pattern seen on ECGs.

• Atypical atrial flutters do not have this pattern and are therefore harder to identify. They can be found:

  • running clockwise in the right atrium

  • in the left atrium

  • around sites of previous surgery

What is the most common cardiac arrhythmia?

Atrial fibrillation, followed by atrial flutters.

Conditions predisposing to an atrial flutter

• High blood pressure

• Congenital heart disease

• Ischaemic heart disease

• Pericarditis

• Cardiomyopathy

• Cardiac surgery

• Other disease of the heart

• Over active thyroid valves

• Chronic airways disease (e.g. COPD)

• Pneumonia

• Pulmonary embolism

• Idiopathic

Risk factors for atrial flutter

• Male

• Increasing age

• Excess alcohol

• Family history of arrhythmias

What is atrioventricular node re-entrant tachycardia (AVNRT)?

A re-entrant SVT where the circuit loops in or around the AVN. This is because there are two pathways of varying speeds (one slower, one faster) in or around the AVN, and the impulse can travel backwards into the atria via one pathway (usually the fast one) from the other pathway (usually the slow one).

What are the predisposing conditions to AVNRT?

• Coronary artery disease, heart valve disease and other heart diseases.

• Heart failure.

• Heart condition present at birth, called a congenital heart defect.

• Previous heart, lung or throat surgery.

• Obstructive sleep apnea.

• Thyroid disease.

• Lung diseases such as chronic obstructive pulmonary disease (COPD).

• Diabetes that is not controlled.

Risk factors for AVNRT

• Young women

• Some medicines, including those used to treat asthma, allergies and colds.

• Emotional stress.

• Caffeine.

• Excessive alcohol use.

• Smoking and using nicotine.

• Stimulant drugs, including cocaine and methamphetamine.

What is atrioventricular re-entrant tachycardia (AVRT)?

A re-entrant SVT where there is an accessory pathway (additional pathway) between the ventricles and atria through which a re-entry loop is created, causing tachycardia. There are two types:

• Orthodromic - normal AVN conduction, then the impulse travels back up into the atria through the accessory pathway.

• Antidromic - the impulse travels down the accessory pathway and then back up via the normal conduction pathway.

What are the predisposing conditions for AVRTs?

The accessory pathway is typically present from birth. The most common congenital heart condition associated with this is Wolff-Parkinson-White syndrome (not usually genetic).

What are ventricular tachyarrhythmias?

A wide complex tachyarrhythmia originating from the ventricles.

What are the two different types of ventricular tachyarrhythmias?

• Ventricular tachycardia

• Ventricular fibrillation

What is ventricular tachycardia?

A regularly irregular tachyarrhythmia originating in the ventricles. It can be focal, or re-entrant, however both are dangerous.

Focal ventricular tachycardia causes

It is caused by the ventricular pacemaker cells (usually too slow to take over from the SAN) becoming stressed or irritated. This makes them fire at a faster rate, taking over from the SAN. They can be irritated by:

• Medications

• Illicit drugs (stimulants - e.g. cocaine or methamphetamine)

• Electrolyte imbalances

• Myocardial Ischaemia or previous MI

• Structural heart disease

• Congenital heart conditions (e.g. Long QT syndrome)

What is more likely - focal or re-entrant ventricular tachycardia?

Re-entrant.

What causes re-entrant ventricular tachycardia?

Scarring / structural disease creating two pathways in the ventricular myocytes. If one pathway is slower than the other, then impulses can create a loop, triggering continual ventricular contractions. Causes of this include:

• Ischaemic cardiomyopathy (main cause)

• Dilated cardiomyopathy (2nd most common cause)

• Other structural heart diseases and cardiomyopathies

What is ventricular fibrillation?

A very dangerous ventricular tachyarrhythmia where the contractions in the ventricles become completely disorganised and chaotic.

What causes ventricular fibrillation?

The cause is not always clear, but it is thought it is usually caused by the myocytes becoming stressed or damaged, and therefore structurally or electrically changed - tissue heterogeneity. This means the cells contract abnormally. Some causes of this include:

• Medications

• Illicit drugs (stimulants - e.g. cocaine or methamphetamine)

• Electrolyte imbalances

• Myocardial Ischaemia or previous MI

Are all SVTs narrow complex?

No, in some scenarios SVTs can be wide complex - typically AVRT associated with WPW syndrome is wide complex.

What are the general potential consequences of tachyarrhythmias?

• It shortens diastole, reducing ventricular filling and coronary perfusion.

• Loss of effective atrial contraction and synchrony can reduce cardiac output (particularly if the patient already has ventricular dysfunction of valve disease).

• Rapid ventricular activation increases myocardial oxygen demand and may precipitate ischaemia.

• Persistent tachycardia can cause a reversible tachycardia-induced cardiomyopathy.

• VT and VF cause severe loss of effective output and can precipitate death.

• VF is incompatible with a pulse.

Typical presentation of atrial tachycardia

• Typically paroxysmal, but can be persistent

• Tends to have abrupt onset and offset

• Palpitations

• Fatigue

• Pre-syncope/syncope

• Chest pain

• Dyspnoea

• Multifocal atrial tachycardia can be masked by other illness

• Can be asymptomatic (in healthy young people, it can appear when they sleep)

Typical presentation of junctional rhythms

• Can be persistent or paroxysmal

• Can be abrupt or gradual onset

• Can be symptomless

• Anxiety

• Chest pain

• Dizziness

• Fainting

• Feeling fatigued or weak

• Heart palpitations

• Shortness of breath

What other arrhythmia is atrial flutter typically associated with?

Atrial fibrillation.

Typical presentation of atrial flutter

• Can be paroxysmal or persistent

• Abrupt onset and offset

• Can be asymptomatic

• Palpitations

• Chest pain

• Fainting or almost fainting

• Shortness of breath

• Feeling very tired

Typical presentation of AVNRT

• Paroxysmal episodes that have abrupt onset and offset

• Can be asymptomatic, but this is not as common

• Heart palpitations — this is the most common symptom

• Feeling like your heart is racing

• Dizziness

• Palpitations or discomfort in your neck

• Producing more pee than usual (polyuria)

• Shortness of breath

Typical presentation of AVRT

• Typically paroxysmal with abrupt onset and offset

• Often symptomatic

• Heart palpitations

• Chest pain

• Lightheadedness

• Dizziness

• Shortness of breath

• Fatigue

Typical presentation of ventricular tachycardia

• Can be paroxysmal or sustained (>30 seconds)

• Abrupt onset and offset

• Can be asymptomatic

• palpitations (a thumping or fluttering feeling in your chest)

• chest pain or discomfort

• difficulty breathing

• feeling sick

• sweating a lot

• feeling light-headed or passing out (fainting)

Typical presentation of normal sinus tachycardia

• Gradual onset

• Paroxysmal with identifiable trigger

• Faster heartbeat.

• Palpitations.

• Fainting.

• Chest pain.

• Lightheadedness.

• Difficulty breathing.

• Dizziness.

Managing sinus tachycardia

• In most cases, sinus tachycardia is a normal response to environmental triggers, and requires no treatment.

• If the sinus tachycardia has a clear cause and is troubling the patient, then the trigger should be avoided / managed (e.g. treating anxiety, avoiding caffeine etc.)

• If the sinus tachycardia is inappropriate and interfering with the patients life then medications to slow the heart rate down may be used:

  • Beta blockers

  • Calcium channel blockers

  • Ivabradine

  • It is also important the patient stays active, as this can improve symptoms.