Arrhythmia is a condition wherein there is an abnormal rhythm of the heartbeat. It could present as irregular, too fast or too slow heartbeats. Arrhythmia can be caused by an underlying condition such as coronary artery disease, congenital heart defect, myocardial infarction, defective heart valves, hyperthyroidism and lack of potassium. Scarring of the heart tissue or changes in its structure can lead to arrhythmias as well. It can also be due to external factors that stimulates the heart such as stress, caffeine, alcohol, nicotine, cocaine and drug stimulants.
In a normal heart, the electrical impulse starts at the sinus node in the right atrium. The electrical impulse travels to the atria causing atrial contraction. It then travels to the atrioventricular node. The impulse slows down when it passes the AV node to allow the ventricles to fill with blood before contraction. Once the electrical impulse reaches the ventricles, the ventricles contract and pump the blood. The normal resting heart rate is 60 to 100 beats per minute. During an arrhythmia, these electrical impulses are not coordinated causing the change in the heartbeat.
Types of arrhythmia based on the speed:
- Bradycardia is a slow heart rate which is at most 50 beats per minute.
- Tachycardia is a rapid heart rate with at least 100 beats per minute.
- Fibrillation manifests with rapid, but uncoordinated heartbeats.
Types of arrhythmia based on the rhythm and origin:
- Atrial premature contraction (APC) is commonly observed in healthy individuals. The heart rhythm is briefly interrupted by a heartbeat that occurred earlier than normal. The person will feel a skipped heartbeat followed by a forceful heartbeat.
- Ventricular premature contraction causes a premature contraction of the ventricles. An abnormal action potential occurs when a region in the heart outside of the conduction system becomes more excitable than normal. This premature heartbeat is usually caused by emotional stress, excess caffeine, nicotine or alcohol, and lack of sleep.
- Supraventricular tachycardia (SVT) originates from the atria. The person usually has a heart rate of 160 to 200 beats per minute. This type of arrhythmia suddenly begins and ends. Sometimes, the heart rate can be decreased without the use of antiarrhythmic drugs.
- Ventricular tachycardia (VT or V-tach) presents with ventricles that beat rapidly (at least 120 beats per min) due to four or more ventricular premature contractions. Prolonged VT does not allow the ventricles to fill and pump blood sufficiently. This can lead to low blood pressure, heart failure or ventricular fibrillation.
- Heart block results in a slow transmission of nerve impulses between the atria and ventricles due to the blocked electrical pathways. The most common kind is the atrioventricular (AV) block. In first-degree AV block, the conduction through the AV node is only slower than normal. In second-degree AV block, some nerve impulses are not transmitted to the AV node. In third-degree AV block, all nerve impulses are not transmitted to the AV node and manifests with a ventricular contraction rate of at most 40 beats per minute.
- Atrial flutter presents with a second-degree AV block and a heart rate of 240 to 360 beats per minute.
- Atrial fibrillation (AF) commonly occurs in older patients. Atrial pumping stops because of the unsynchronized contraction of the atrial fibers. Heart rate can reach 300 to 600 beats per minute. The atria and ventricles fail to beat in rhythm resulting in an irregular timing and strength of the heartbeat. There is a risk of stroke when the blood remains in place and forms blood clots.
- Ventricular fibrillation (VF or V-fib) is the most fatal arrhythmia. The ventricles only tremble instead of contract because the ventricles are completely asynchronous. The ventricles fail to pump and eject blood leading to circulatory failure and death. Inadequate blood flow to the heart during heart attack most commonly causes V-fib. Other causes include cardiovascular shock, electrical shock, drowning and lack of potassium. A V-fib patient immediately becomes unconscious. If left untreated, seizures occur after 5 minutes and death soon follows.
Some arrhythmias may not present with any signs and symptoms. The diagnosis of arrhythmia is based on medical history and heart-monitoring tests. Diagnostic tests include electrocardiogram (ECG), holter monitor, event monitor, echocardiogram and implantable loop recorder.
Commonly Prescribed Drugs
Antiarrhythmic drugs are for patients with tachycardia or premature heartbeats. Currently, there are no drugs that can manage bradycardia. Some of these drugs are proarrhythmics. It can worsen or cause arrhythmias while treating an existing arrhythmia.
- Digoxin is effective for patients with atrial fibrillation, atrial flutter or supraventricular tachycardia. It reduces the speed of electrical impulses through the AV node. Side effects: nausea, vomiting, yellow-green colorblindness
- Sodium channel blockers slow down the transmission of electrical impulses on the heart. These drugs can address arrhythmias that originate from the atria and ventricles. Examples include disopyramide, lidocaine, quinidine and mexiletine. Side effects: arrhythmia, tremor, dizziness
- Calcium channel blockers (CCBs) are given to patients who have arrhythmia, angina and abnormal blood pressure. CCBs dilate the blood vessels to improve blood flow towards the heart. These drugs are for long-term use. Only diltiazem and verapamil are effective CCBs for arrhythmias. Side effects: tachycardia, dizziness, constipation
- Beta blockers inhibit the action of epinephrine relieving a fast heartbeat. It can decrease the blood pressure and the workload of the heart. This drug class is effective for arrhythmias that originate from the ventricles. These drugs are not given to patients with asthma or diabetes. Examples include atenolol, bisoprolol and metoprolol. Side effects: tiredness, cold hands, headache
- Potassium channel blockers suppress tachyarrhythmia that occurs when there is a premature ventricular contraction. Examples include amiodarone, bretylium, dofetilide and sotalol. Side effects: arrhythmias, low blood pressure
- Amiodarone reduces the speed of electrical impulse conduction in the AV node. It is mostly used for paroxysmal supraventricular tachycardia. This is contraindicated for asthmatic patients. Side effects: flushing, spasms of the airways
Anticoagulants are commonly given to patients with arrhythmia that causes the blood to become stagnant such as atrial fibrillation. These drugs do not address the arrhythmia, but it prevents formation of blood clots. Warfarin is a commonly prescribed anticoagulant. Side effects: bloody stool and multiple bruises (indicative of internal bleeding)
Treatment and Management
Tachycardia can be managed by vagal maneuvers. Some methods include straining as if experiencing constipation, rubbing the area over the carotid artery in the neck (not for people older than 50) and submerging the face in a bowl of ice-cold water. This is usually effective for supraventricular tachycardia.
Minimize the risk factors by maintaining a healthy body. Exercise regularly and eat a heart-healthy diet low in salt and saturated fat. Maintain blood pressure, cholesterol and sugar levels under control. Quit smoking and drink alcohol in moderation.
Medical Devices and Procedures
A pacemaker can be implanted under the skin near the collarbone. Wires from the pacemaker are attached on the heart and send out electrical impulses if the heartbeat becomes abnormal.
- Cardioversion is done on certain arrhythmias like atrial fibrillation and ventricular fibrillation. The heart is shocked using paddles or patches (defibrillator) on the chest to restore the normal rhythm of the electrical impulses.
- Catheter ablation involves the use of electrode-tipped catheters. These catheters are inserted through the blood vessels to the heart to reach the region that causes the arrhythmia. A small region of the heart tissue is damaged using heat, extreme cold or radiofrequency energy to create an electrical block and stop arrhythmia.
- Implantable cardioverter-defibrillator (ICD) is similar to a pacemaker. It has wires attached on the heart and monitors the heart rhythm. An abnormality in the heart rhythm prompts the ICD to send out low- or high-energy shocks to reset the rhythm.
A surgeon can do a maze procedure on the heart if other treatments fail. A series of surgical incisions is made on the atria. This maze of scar tissue will not conduct electricity. Thus, stray electrical impulses are prevented.