Types of Arrhythmias
Arrhythmias can be classified as follows (NHLBI 2011a):
Premature (Extra) Beats
Premature extra beats are a very common and mostly harmless type of arrhythmia. Those that occur in the atria are called premature atrial contractions (PACs), while those occurring in the ventricles are called premature ventricular contractions (PVCs) (Hebbar 2002b; Cha 2012). Premature atrial contractions have been linked to excess consumption of caffeine and alcohol, the use of sympathomimetic medications (drugs that mimic the effects of sympathetic nervous system signaling molecules called catecholamines), and are sometimes present in people who have structural heart disease (Hebbar 2002b). Premature ventricular contractions are often seen in the presence of structural heart disease, but they can also appear in the absence of any identifiable heart conditions (Cha 2012).
Premature Ventricular Contractions
Premature ventricular contractions (PVCs) are a transient ventricular arrhythmia that can cause the feeling of a “skipped beat” in the chest; they are typically benign in people without structural heart disease. PVCs are fairly common and are estimated to affect 1-4% of the general population, but they are much more common in the elderly, with a prevalence of 69% in individuals older than 75 (Cha 2012; Adams 2012).
Common causes of PVCs include electrolyte imbalance (eg, low levels of magnesium or potassium), ingestion of stimulants (eg, coffee), alcohol, and/ or exercise (Hebbar 2002a; MayoClinic 2011b). While PVCs are typically asymptomatic, they can sometimes cause signs and symptoms such as palpitations, chest pain, and heart failure. However, in the absence of structural heart diseases, PVCs rarely develop into serious arrhythmias (Hebbar 2002a; Cha 2012; Adams 2012).
- PVC-induced cardiomyopathy is a condition in which the heart becomes enlarged and unable to pump blood efficiently due to very frequent PVCs. This condition is a diagnosis of exclusion, (ie, any underlying heart disease causing frequent PVCs must first be ruled out). A treatment called catheter ablation is performed in patients with over 10, 000-20, 000 PVCs in a 24-hour period. This procedure involves using electrical impulses or extreme cold to destroy the abnormal heart tissue that is causing the PVCs; the intervention usually stops the PVCs (Lee 2012; MayoClinic 2011a; Adams 2012).
Supraventricular arrhythmias start in the atria or in the atrioventricular node. Types of supraventricular arrhythmia include atrial fibrillation, atrial flutter, paroxysmal supraventricular tachycardia, and Wolff-Parkinson-White (WPW) syndrome (Hebbar 2002b; MayoClinic 2011a).
Atrial fibrillation is a common type of serious arrhythmia (NHLBI 2011b). The incidence of atrial fibrillation increases with age, with 0.1% of individuals under 55 years and approximately 10% of those over 80 being affected (Schmidt 2011; Go 2001). Post-operative atrial fibrillation, a common form of atrial fibrillation, occurs in 25-40% of patients following cardiac surgery (Gu 2012).
Atrial fibrillation involves the fast and irregular contraction of the atria. In atrial fibrillation, the heart's electrical signals are not initiated in the SA node; instead, they start in another part of the atria or in the nearby pulmonary veins. As the electrical signals do not travel along the normal path, their spread throughout the atria occurs in a rapid and disorganized way. This causes the atria to fibrillate (quiver in an abnormal manner), and blood is not pumped into the ventricles the way it should be (NHLBI 2011b). Atrial fibrillation is usually not life threatening, but can be dangerous if it causes the ventricles to beat very fast (NHLBI 2011b).
Atrial fibrillation has two major potential complications—ischemic stroke and heart failure (NHLBI 2011b; Gutierrez 2011; Knecht 2010).
- Ischemic stroke may develop due to the incomplete emptying of blood from the atria, which facilitates the formation of blood clots within the heart. These clots, if they travel to the brain, may cause an ischemic stroke. Anticoagulant medications (eg, warfarin [Coumadin®]) are typically used as a stroke-prevention strategy for patients with atrial fibrillation.
- Heart failure may occur if the heart is unable to pump enough blood to the body. This occurs if the ventricles do not completely fill with blood.
Atrial flutter, another common pathological supraventricular tachycardia, occurs much less frequently than atrial fibrillation. Atrial flutter differs from atrial fibrillation in that the electrical signals move through the atria with a fast, but regular rhythm. Symptoms and complications of atrial flutter are similar to those of atrial fibrillation (NHLBI 2011b; Link 2012).
Paroxysmal Supraventricular Tachycardia
Paroxysmal Supraventricular Tachycardia (PSVT), the most common supraventricular tachycardia, refers to a fast heart rate that occurs from ‘time to time’. Symptoms of PSVT may begin and end suddenly. In PSVT, electrical signals can be transmitted in the reverse direction from the ventricles to the atria, causing extra heartbeats. PSVT may occur as a result of toxicity due to the medication digitalis, or in association with conditions such as Wolff-Parkinson-White (WPW) syndrome.
- Wolff-Parkinson-White (WPW) syndrome is a type of PSVT wherein the electrical signals travel along an extra pathway from the atria to the ventricles, thereby disrupting the timing of the signals and causing rapid beating of the ventricles. While WPW can be life-threatening, other types of PSVT are typically not life-threatening and can occur without symptoms (Hebbar 2002b; NIH 2012b; Link 2012).
Ventricular arrhythmias are initiated in the ventricles and represent the most common cause of sudden cardiac death. They can be life-threatening and require emergency medical care. Normally, these arrhythmias occur in patients with structural heart problems, but they may sometimes occur in patients who lack evidence of cardiac disease (Roberts-Thomson 2011).
Ventricular tachycardia is a fast (greater than 100 beats per minute) but regular beating of the ventricles that can last from a few seconds to much longer. While mild episodes may not be life threatening, continued ventricular tachycardia that lasts for more than a few seconds is dangerous and may evolve into ventricular fibrillation, which can be fatal (Hebbar 2002a; NHLBI 2011b). It is important to keep in mind that individuals with ventricular tachycardia may sometimes have minimal symptoms (Compton 2012; MayoClinic 2011a; Piccini 2012; Hebbar 2002a).
As its name suggests, ventricular fibrillation (v-fib) makes the ventricles quiver due to disorganized electrical signals. When this happens, the heart is unable to pump blood to the body and death may occur within minutes. V-fib is treated by using a machine known as a “defibrillator” to deliver an electrical shock to the heart and restore its normal rhythm (NHLBI 2011b).
Bradyarrhythmia, or slow heart rate, is defined in adults as a heart rate of less than 60 beats per minute. This may cause insufficient blood to reach the brain. Except for certain individuals, such as people who are very physically fit, in whom a slower heart rate can be normal, bradyarrhythmias may occur as a result of serious medical conditions (eg, heart attacks), medication(s) (eg, beta-blockers and calcium-channel blockers), hypothyroidism, and electrolyte imbalances in the blood (NHLBI 2011b).