Tachyarrhythmia

Tachyarrhythmia is a type of abnormal cardiac rhythm and is classified based on its site of origin as ventricular (originating below the bundle of His) or supraventricular (above the bundle of His). Ventricular tachyarrhythmias include ventricular tachycardia (VT), ventricular fibrillation (VF), and premature ventricular contraction (PVC). Supraventricular tachycardia (SVT) or paroxysmal supraventricular tachycardia (PSVT) presents a rapid heart rate anywhere between 150-250 beats per minute and is further classified as atrioventricular nodal reentrant tachycardia (AVNRT), atrioventricular reciprocating tachycardia (AVRT), atrial tachycardia (AT), atrial fibrillation and atrial flutter. The clinical presentation of tachyarrhythmias may vary depending on the type of arrhythmia from asymptomatic to chronic and recurrent or highly symptomatic and life threatening. Common symptoms in all tachyarrhythmias include palpitations, chest discomfort, dyspnea, fatigue, lightheadedness, and dizziness. Uncommon symptoms comprise diaphoresis, nausea, presyncope, and syncope.

VT is a tachyarrhythmia of >100 beats per minute which is regular while VF is a more serious type of tachyarrhythmia with an asynchronous discharge of impulses causing the heart to beat erratically, often at a rate > 300 beats per minute. This results in poor perfusion of organs, especially the brain, with possible fatal outcomes. VF is commonly seen in individuals with cardiac disease or a recent history of myocardial infarction. PVCs are a less serious type of tachyarrhythmia with the ventricle contracting prematurely and out of sequence to the normal heart beat. They often start suddenly without a warning and can be stimulated by caffeine, chocolate, and some medicines.

The commonest type of SVT is AVNRT which affects young, healthy women [1], often without structural cardiac disease, though some patients may have pericarditis, previous myocardial infarction, or mitral valve prolapse [2]. AVRT is the second most common type of SVT and is caused by accessory tracts which conduct the abnormal impulses proximally as well as distally creating a reentry circuit [3]. AVRT can occasionally occur with Wolff-Parkinson-White syndrome and may spontaneously degenerate into atrial fibrillation [4]. AT is the third most common type of SVT arising from a focus in the atrium [5]. It is of two types: focal and multifocal AT (MAT). Focal AT originates from a definite focus like the crista terminalis in the right atrium or the ostia of the pulmonary veins in the left atrium [6] [7]. MAT is frequently seen in patients with congestive heart failure or chronic obstructive pulmonary disease [6]. SVT symptoms depend on the patient's age, comorbid medical conditions, and duration of the episodes.

Atrial fibrillation (AF) is a type of SVT and a common cause of stroke and congestive heart failure [8]. Atrial flutter is an irregular SVT originating in the atria which may be asymptomatic in the initial stages or may be associated with palpitations, later degenerating into AF. Wolff-Parkinson-White syndrome is characterized by abnormal accessory conduction pathways (bundle of Kent) between the atria and the ventricle.

Tachyarrhythmias can be detected by history and physical examination but the diagnosis is confirmed by a 12-lead electrocardiogram (ECG) or a rhythm strip. Often SVT episodes are misdiagnosed as anxiety or panic attacks especially in the presence of a psychiatric disorder [8]. A high index of suspicion is, therefore, important to make a diagnosis [9]. The initial evaluation should determine whether a patient is hemodynamically stable. A brief cardiovascular examination will determine the ventricular rate and its regularity while the nature of the jugular venous pulse waves may also help to detect tachyarrhythmias. In a stable, symptomatic patient, it is important to obtain a 12-lead ECG while a rhythm strip is an initial assessment measure in an unstable patient prior to emergency cardioversion.

The ECG findings are characteristic for each tachyarrhythmia. A supraventricular origin of the tachyarrhythmia is indicated by a narrow QRS complex (< 0.12 sec) while a wide QRS complex (≥ 0.12 sec) indicates a ventricular origin or an SVT conducted by an intraventricular conduction defect or preexcitation in the Wolff-Parkinson-White syndrome. AF features are irregular, continuous, rapid beats at a rate >300 beats/ minute without discrete P waves. If the P waves are discrete and vary with every beat with at least 3 different morphologies then it is suggestive of MAT. Atrial flutter appears as regular, discrete, uniform P waves without intervening isoelectric periods at rates > 250 beats/min while AT features include regular, discrete, uniform, abnormal P waves with intervening isoelectric periods at rates < 250 beats/min. In VF, the rhythm strip will show rapid, irregular heart rate up to 300 beats/ minute. If the QRS complex varies with every beat, then the tachyarrhythmia is called polymorphic VT and the most notorious form of polymorphic VT is torsades de pointes.

Laboratory tests should include serum electrolytes, calcium, phosphate, as well as cardiac troponin level assessment. Echocardiography helps to assess the status of the heart while Holter monitoring is indicated in patients with recurrent tachyarrhythmias. Other tests like stress test may be performed as indicated during the clinical evaluation of the patient.

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