Cardiac Arrhythmias

An arrhythmia is defined as the irregular rhythm of the heartbeat. The irregular rhythm could either be too slow or too fast (either less or more than the normal rate). Arrhythmias occur due to disturbances in the normal activation of the myocardium by cardiac impulses. Normal activation of the myocardium results in sinus rhythm, which is the normal rhythm of the heartbeat. Arrhythmias disturb the sinus rhythm of the heart. They can occur at any age, and their severity depends on associated cardiac structural changes.

The exact mechanism by which cardiac arrhythmias are caused is not fully understood and can vary according to the type of arrhythmias. Release of excess catecholamines from the body during stress, rapid changes in blood pressure, loss of oxygen flow to the cardiac tissue, inflammation or infection of the underlying cardiac muscle, anti-arrhythmic drugs, and increased demand for oxygen due to any physiological or pathological cause can cause cardiac arrhythmias.

Depending on the clinical features, site of involvement, and mechanisms, cardiac arrhythmias can be classified into various types.

Cardiac arrhythmias according to the heart rate are classified into:

• Bradyarrhythmia- irregular rhythm with heart rate less than 60 beats per minute.
• Tachyarrhythmia- irregular rhythm with heart rate more than 100 beats per minute.

Cardiac arrhythmias according to the mechanism are classified into:

• Arrhythmias due to abnormal pulse formation include sinus arrhythmia, atrial arrhythmia, ventricular arrhythmia, and atrio-ventricular junction arrhythmia.
• Arrhythmias due to defects in impulse conduction include sinus-atrial block, intra-atrial block, atrio-ventricular block, intra-ventricular block.

Cardiac arrhythmias occur worldwide in people of every age and race. The most common type of these arrhythmias is atrial fibrillation. There is no gender preference, but certain arrhythmias such as atrial fibrillation (AF) occur more commonly in men than women. Risk factors for cardiac arrhythmias include:

• Advancing age 
• Hypertension
• Diabetes
• Obesity
• Previous history of any cerebrovascular event
• Previous history of any cardiac event
• Family history of cardiac illnesses
• Genetic factors
• Alcohol and drug use
• Certain endocrine and neurologic disorders
• Cardiac surgery

Signs and symptoms of cardiac arrhythmias include:

• Irregular pulse
• Bradycardia or tachycardia (abnormal heart rate)
• Palpitations
• Chest pain or discomfort
• Shortness of breath
• Distended neck veins
• Diminished breath sounds
• Abnormal heart sounds and murmurs on auscultation
• Clubbing
• Edema
• Fatigue
• Poor exercise tolerance
• Generalized weakness
• Dizziness
• Syncope

Complications of cardiac arrhythmias include:

• Stroke
• Myocardial infarction
• Heart failure
• Disseminated intravascular coagulation 
• Bleeding tendencies due to anticoagulation
• Dementia 
• Pulmonary embolism
• Death

• Diagnosis of arrhythmias is usually made on history, physical examination, and 12 lead echocardiography (ECG). It looks at the characteristics such as the type, duration, frequency of symptoms, precipitating and relieving factors, previous history of cardiac disease, etc.
• The 12 lead ECG is used to observe heart rate, heart rhythm, ECG complexes, interval and the waves, conduction delays or blocks, absence of acute or prior myocardial infarction.
• Other than that, transthoracic echocardiography can help detect structural defects such as valvular heart disease, atrial and ventricular pressures, wall motion defects, presence of thrombi, etc.
• Lab studies that aid in the diagnosis includes complete blood count, serum electrolytes, cardiac enzyme levels, b-type natriuretic peptide (BNP), d-dimers, thyroid function tests, toxicology screening, and digoxin level.
• Imaging studies such as CT scanning and MRI can also be used.
• Other tests include exercise testing, Holter monitoring, and electrophysiology studies.

Differential diagnoses of cardiac arrhythmias include the distinction between different types of arrhythmias. Other related disorders in the differentials include:

• Sinus tachycardia
• Premature ventricular contractions (PVCs)
• Congestive heart failure
• Vaso-vagal syncope
• Hyperthyroidism
• Hypoglycemia
• Drug-related
• Wolf Parkinson White (WPW) syndrome
• Atrial flutter

The mainstay of treatment against cardiac arrhythmias is to restore normal cardiac rhythm, treat underlying functional or structural pathology and prevent coagulation of blood due to irregular rhythm of the heart.

• Patients at an increased risk, such as those with advanced age, comorbid conditions like hypertension or diabetes, or prior history or family history of cardiac diseases, are put on anticoagulation therapy.
• Patients at an increased risk of bleeding due to the anticoagulation therapy are put on alternative therapies such as cardioversion devices, electrical cardioversion, catheter-based devices, etc.
• The rate can be controlled through pharmacologic intervention or insertion of pacemakers.
• Rhythm can be controlled through drugs, electrical cardioversion, or ablation through surgical intervention. However, it should be noted that all the medications used to treat rhythm defects can induce arrhythmias as a side effect and should be used with great precaution.

• Anticoagulation is achieved by drugs such as warfarin, dabigatran, and rivaroxaban, etc.
• Drugs to control heart rate include beta-blockers, calcium channel blockers, digoxin, etc.
• Rhythm can be controlled by anti-arrhythmic drugs such as amiodarone, flecainide, etc.

The prognosis of cardiac arrhythmias depends upon the type of arrhythmia and associated structural changes in the heart. With advancing age, the morbidity and mortality associated with these also increase. The most common type of cardiac arrhythmia, atrial fibrillation (AF), is associated with the highest mortality (almost 2-fold greater risk of death). Its association with thromboembolic events can prove fatal for the patient.

Cardiac arrhythmias can be prevented by the prevention of risk factors.

• Comorbid conditions such as hypertension and diabetes should be regularly monitored and kept in check with compliance to the prescribed treatment regimen and lifestyle choices.
• Stimulating substances that can affect the heartbeat should be used very carefully. These include everyday products such as coffee, tea, alcohol, cough medications, appetite suppressants, recreational drugs such as marijuana, cocaine, methamphetamines, and nicotine.
• Certain drugs that can cause the irregular rhythm of the heart should be used with great precaution. These include psychotropic drugs, anti-arrhythmic drugs, beta-blockers, calcium channel blockers, etc.
• Maintain normal body mass index by reducing extra body weight and exercising regularly.
• Balanced diet that promotes cardiovascular health should be used.
• Diagnosed patients who have assistive devices such as pacemakers or cardioverters should monitor their pulse regularly. Any changes in the rate and rhythm should be taken very seriously for seeking immediate medical care.