From Dr Andrew To, Cardiologist, WDHB
Arrhythmia is a problem with the rate or rhythm of our heartbeat. The heart can beat too fast, too slow, or with an irregular rhythm.
Tachycardia is the term that refers a heart beat that is too fast. Bradycardia describes a heart beat that is too slow.
Arrhythmia encompasses a diverse range of conditions, some harmless, but some serious or even life threatening.
Arrhythmias are more common in people with heart diseases. This includes heart attacks (myocardial infarction), heart failure, abnormal thickening of heart tissue, heart valve problems, congenital heart disease (heart defects present at birth). Other conditions can also cause arrhythmia, including high blood pressure, diabetes, and abnormal thyroid function.
Normal Conduction System 正常心臟傳導系統
Normal heart function relies four components
- heart muscle contraction
- normal valve function
- coronary arteries providing blood supply and nutrients
- conduction system coordinating the pumping of blood through the atria and the ventricles
Conduction system is our heart’s internal electrical system, controlling the rate and rhythm of our heartbeat. With each heartbeat, an electrical signal spreads from the top of the heart to the bottom. The electrical signal stimulates the heart contraction. The normal heartbeat with its subsequent electrical propagation is often referred to as the normal sinus rhythm.
The intrinsic pacemaker sits in a group of cells called the sinoatrial (SA) node, where each electrical signal originates. At rest, our SA nodes send an electrical signal 60-100 times a minutes, making our normal pulse rate at 60-100 a minute.
我們心臟本身的起搏器位於竇房結的一組細胞，是心臟電流信號的起源。人休息時，竇房結每分鐘發送 60-100 次信號，使我們的正常脈搏率大約在每分鐘 60-100。
The electrical signal from the SA node travels through the atria (the upper collecting chambers of the heart), causing it to pump blood into the heart’s ventricles (the lower pumping chambers).
The signal reaches a group of cells at the atrioventricular (AV) node, located between the atria and the ventricles. There is a slowing of the signal at this point to allow for the ventricles to fill after atrial contraction.
Finally, the electrical signal leaves the AV node and rapidly travels the bundle of His and the Purkinje fibres to activate the rest of the ventricles. The end result is the ventricular contraction and pumping of blood to the lungs and the rest of the body. This process is rapid, so that the entire ventricle is coordinated in contracting at the same time to maximize the pumping efficiency.
A problem with any part of this process can cause an arrhythmia.
Diagnosing arrhythmia 診斷心律不整
Arrhythmia covers a wide range of conditions. Most arrhythmias are harmless, but some are not. The outlook depends on the type and severity of the arrhythmia. Establishing the right diagnosis is most important.
Many arrhythmias cause no symptom. This is part of the reason for heart attack patients to be admitted to the coronary care unit, where arrhythmias are actively looked for and treated.
In others, arrhythmias can present as
- palpitations (heart flutters)
- a fast heart beat
- a slow heart beat
- an irregular heart beat
- pauses between heart beats
Other more serious symptoms include
- dizziness, lightheadedness
- fainting, near-fainting, collapse
- fatigue, weakness
- chest pain
- shortness of breath
ECG (electrocardiogram) is the cornerstone of diagnosing arrhythmias. Using leads on the chest, arms and legs, the ECG records the heart’s electrical activity and diagnoses abnormal heart rate and rhythm. Its limitation, however, is the fact that a standard ECG only records the heartbeat for a few seconds. In arrhythmias that come and go, other tests may have to be done.
A Holter monitor records the heart’s electrical signals for a full 24 or 48 hours. Every heartbeat is counted and analyzed, when we do our normal daily activities. When symptoms occur, we can correlate back to the ECG and see what caused the event.
攜帶式心電圖記錄檢查監視 24 或 48 小時的心臟電流活動，完整的分析每一次心跳，讓症狀發生時可以看看心電圖的診斷是甚麼。
An event monitor is similar to the Holter monitor, but can be worn for longer, e.g. a week or two. However, it requires the patient to push a button to start recording when symptoms are felt. Again, the ECG gives information about what the symptoms were caused by.
In rare cases, implantable loop recorder can be surgically placed under the skin in the chest area, in order to figure out what arrhythmia is causing the patients’ symptoms. These recorders are left for as long as 1-2 years and are used in more serious cases of suspected arrhythmia.
在少數情況下，為了弄清楚患者的嚴重症狀是從那一種心律不整的病症引起，患者可能需要利用手術在胸前皮膚下放置植入式循環記錄器，記錄長達 1-2 年的心臟電流活動。
Echocardiography is often used in the workup of arrhythmia, despite the fact that it does not record the heart’s electrical activities. This ultrasound examination gives information about the function of the heart muscles and heart valves. If abnormal, the chance of sinister arrhythmia is much higher.
Electrophysiology study (EPS) is used to assess serious arrhythmias. It is an invasive procedure that involves the passing of thin flexible electrodes through the groin veins and arteries to the heart, in order to record the heart’s electrical signals. The wires can also stimulate and trigger an arrhythmia, in order to make the correct diagnosis. Catheter radiofrequency ablation may be performed during EPS, if it has been determined that the patient’s specific arrhythmia can be treated by delivering a special energy through the ablation catheter and destroying small areas of heart tissue responsible for the arrhythmia.
Important types of arrhythmia 一些心律不整重要的類型
The clinical characteristics, presentation, prognosis and treatment of arrhythmias differ according to its type.
Bradyarrhythmias occur when the heart rate is slower than normal. When the heart rate is too slow, the brain does not receive enough blood, and causes patients to pass out.
Not all patients with a heart rate slower than 60 beats per minute has bradyarrhythmia, as those who are physically fit can often have slow heart rates. In others, bradyarrhythmias can be dangerous and life threatening.
不是所有心臟速度慢於每分鐘 60 次的人，就患上心動過緩，例如有強健體魄的人，往往有慢心率。在某些情況下，心動過緩可以是危險，甚至危及生命的。
Bradyarrhythmias can be caused by a variety of conditions, including
- heart attacks
- electrolyte imbalance (e.g. potassium, calcium…)
- medications that slow down our heart rate (e.g. beta-blockers, calcium channel blockers…)
- conditions that alter the heart’s electrical activity, including an underactive thyroid gland
The ECG is most helpful in sorting out the underlying diagnosis, its prognosis and therefore treatment. In many with bradyarrhthmias, a pacemaker is necessary.
A pacemaker is a device implanted under the skin of the chest, with sensors that detect the heart’s electrical activity. When there is a block in the electrical signaling, electrical impulses are sent from the pacemaker to prompt the heart to beat at a normal rate. Most pacemakers only weigh about 20-50 grams and sit under the collarbone. They are smaller than an average matchbox.
心臟起搏器是植入胸部皮膚下的，以電極及導線檢測心臟的電流活動。如電流活動過慢，節律器便會發送電脈衝，使心臟在正常的速度跳動。起搏器大多數僅重約 20-50 克，坐在鎖骨下，小於一般的火柴盒。
Premature beats 早搏
The most common type of arrhythmia is premature beats and is harmless most of the time. In most cases, premature beats happen naturally and do not cause symptoms. If they do, people usually feel a chest fluttering or a feeling of skipped heartbeat. Stress, caffeine or nicotine exacerbates this condition.
Premature beats can originate from the atria, premature atrial contractions (PACs), or ventricles, premature ventricular contractions (PVCs).
In rare cases, premature beats are associated with heart diseases. Excluding structural heart disease may be important in patients with suspected premature beats.
Atrial fibrillation 心房顫動
Atrial fibrillation (AF) is the most common serious arrhythmia, characterized by the fast but irregular activation of the atria.
Electrical signals in the atria spread in a rapid and disorganized manner, resulting in the atrial wall quivering very quickly (fibrillating), instead of beating normally and emptying blood from the atria to the ventricles.
In some people, AF occurs for a short duration of time, coming and going on their own; i.e. paroxysmal AF. In others, AF may be present all the time; i.e. persistent AF.
The result of the atrial fibrillation is that these electrical signals travel to the ventricles at rates of >300 per minute. They cause the ventricles to beat irregularly and too fast. This results in the failure of the ventricles to fill completely with blood, and hence prevent the heart from pumping enough blood to meet the body’s needs. Heart failure ensues, presenting with shortness of breath, poor exercise capacity, ankle swelling, and inability to lie flat at night.
Atrial fibrillation also prevents the emptying of blood from the atria, causing blood clots to form. When a blood clot breaks off and travels to the brain, it can cause a stroke.
Management of atrial fibrillation is often complicated and should always be tailored to the individual patient’s condition. Options include controlling the rapid heart rate with medications, cardioverting patients from atrial fibrillation back to normal sinus rhythm. Cardioversion can either be performed using medicines (chemical cardioversion) or by electrical cardioversion that involves a brief general anaesthetic and a brief low-energy electrical shock to restore normal rhythm.
In addition, the stroke risk should be minimized by the use of blood thinning medications, such as Warfarin or Dabigatran. These medications can cause significant bleeding as potential side effects, hence are recommended in those with moderate-high stroke risk.
In a minority of AF patients who failed medical therapy, ablation procedure can be performed to restore normal rhythm.
Atrial flutter is a similar condition to atrial fibrillation, though less common. The origin of the abnormal electrical signals is different with a fast but regular, instead of irregular, rhythm. However it presents with similar symptoms and has similar complications as atrial fibrillation.
Paroxysmal supraventricular tachycardia (SVT)
SVT is a condition characterized by a very fast heartbeat that begins and ends abruptly. The abnormal electrical signal originates in the area between the atria and the ventricles. Symptoms may include palpitations, with or without dizziness and chest discomfort.
In this type of arrhythmia, vagal manoeuvers can sometimes control the heart rate. These include holding our breath and bearing down (Valsalva manoeuver), coughing and immersing our face in ice-cold water. In others, medications such as adenosine may be needed to restore normal rhythm. Other medications (e.g. beta-blockers) may be used to reduce the occurrence of these arrhythmias. In most cases, if medications are ineffective, radiofrequency ablation is highly effective.
迷走神經刺激有時可以控制這種心搏過速，這包括冰水敷臉法、伐氏操作憋氣法，及咳嗽。其他患者可能需要藥物（如腺苷）恢復正常的節奏； 其他的藥物（如 β-阻斷劑）則減少這種心搏過速發生的機會。在大多數情況下，如藥物無效，射頻導管燒灼術是非常有效的。
Wolff-Parkinson-White syndrome is a special subtype of SVT that involves electrical signals travelling along an extra pathway from the atria to the ventricles. Such extra pathway may cause the abnormal contraction of the ventricles and potentially is life threatening.
Ventricular arrhythmias 心室性心律不整
Ventricular arrhythmias originate from the hearts’ lower chambers, the ventricles; and are dangerous and life threatening. These include ventricular tachycardia and ventricular fibrillation. They usually present in the context of a heart attack (myocardial infarction), weakened heart muscle (cardiomyopathy), or rarer rhythm disorders of the heart.
Both conditions cause significant compromise of heart function and lead to sudden collapse (cardiac arrest) and death within minutes. These arrhythmias are responsible in causing sudden cardiac death in those who had heart attacks.
Treatment is with an electric shock to the heart called defibrillation. This is usually delivered by emergency first responders such as ambulance personnel. Recent use of automated external defibrillator (AED) strategically placed in public spaces has improved the chance of survival from sudden cardiac arrest.
In survivors of sudden cardiac arrest, or in those with a high risk of ventricular arrhythmias, doctors may recommend the use of an implantable cardiac defibrillator (ICD) on top of usual medicines to control the condition. This device is similar to a pacemaker, though slightly bigger. Its role is in detecting ventricular arrhythmias and delivering an internal electrical shock to revive the heart. It has been shown to improve these patients’ long-term survival.