Cardiac arrhythmias

What is cardiac arrhythmia?

The term cardiac arrhythmia refers to pathological changes that affect the transmission of normal electrical impulses in the heart, and result in a slower, faster or irregular heart rhythm. Arrhythmias are divided into atrial and ventricular arrhythmias, depending on where in the heart they originate from. In addition, they are divided according to whether the heart rate is slowed down (bradyarrhythmia) or increases (tachyarrhythmia). Sometimes, cardiac arrhythmias can be life-threatening, or they can lead to the exacerbation of other conditions. One of the most common arrhythmias, for instance, which is known as atrial fibrillation, can increase the risk of stroke, as well as further reducing the efficiency of the heart in patients with heart failure.

It should be noted that normal fluctuations in heart rate, such as those seen in response to excitement or physical exercise, are not classed as arrhythmias. In certain patients with severe symptomatic bradycardia, the implantation of a pacemaker may be necessary.

What are the main symptoms?

The following symptoms may be indicative of arrhythmia:

• Palpitations (a racing heart) or an irregular heartbeat
• Dizziness
• Blurred or darkened vision or syncope (fainting)
• Anxiety and agitation
• Dyspnea (shortness of breath) and reduced exercise capacity
• Chest pain

What are the possible causes of arrhythmia?

The direct cause of arrhythmia is always a disruption in the normal electrical stimulation of the heart - the heart's pumping action becomes uncoordinated or inefficient. Usually, the heart's contraction is coordinated by the sinoatrial node (SA node), a small, electrically active area of the heart muscle. Here, electrical impulses are produced at regular intervals, and then sent via the atria to the ventricles. In some cases, certain pathological changes mean that additional areas can start to produce electrical impulses, or normal impulses may no longer be transmitted properly. These changes may be due to scar tissue affecting the normal structure of the heart, an insufficient supply of oxygen to heart muscle cells, or the effect of hormonal changes on the heart muscle. In short, arrhythmias frequently occur as a result of the following underlying conditions:

• Coronary heart disease and heart attack
• Conduction abnormalities
• Electrolyte imbalance
• Heart valve disease
• Inflammation of the heart muscle
• Disorders of the heart muscle (cardiomyopathies)
• High blood pressure
• An over-active thyroid (hyperthyroidism)
• Certain medicines or drugs

Diagnosis of arrhythmia

• The electrocardiogram (ECG) is the most important diagnostic tool: resting ECG, ambulatory ECG, and exercise ECG using a stationary bike.
• An echocardiogram may provide information on for instance heart valve disease or abnormalities in the way the heart pumps blood around the body.
• Blood tests, including thyroid function tests, may also provide essential information.
• Some cases may even benefit from the use of magnetic resonance imaging (MRI) or catheter-based investigations.

Treatment for arrhythmia

Wherever possible, treatment is targeted at the underlying cause of the arrhythmia and, as a result, it may be possible for the heart simply to return to a normal rhythm following successful treatment of hypothyroidism or heart valve disease. Not all cases of arrhythmia require treatment. However, if the heart's ability to pump blood is impaired, or if a patient suffers from a potentially dangerous arrhythmia, treatment is essential. This may involve:

• Medication
• Pacemaker systems
• Catheter ablation

Medication
Depending on the type of arrhythmia involved, treatment may involve a number of different medicines, which are referred to as anti-arrhythmic drugs.

Pacemaker systems
While traditional pacemakers are primarily used to stimulate the heart in patients with a dangerously low heart rate, some modern devices can resynchronize the pumping action of the ventricles to ensure that they contract in a coordinated fashion. This is referred to as resynchronization therapy, and is used in patients with severe heart failure to improve the heart's ability to pump blood around the body. In addition to this, implantable defibrillators can be fitted. These devices can automatically detect life-threatening arrhythmias such as ventricular fibrillation and, in response, deliver an electric shock to restore a normal heartbeat. Some modern pacemakers combine all of these features into one device.

Catheter ablation
This specialist procedure allows the physician to ablate (destroy) areas of the heart muscle that are responsible for producing abnormal electrical impulses. In complex cases, this challenging procedure may also be performed using a robotic navigation system. Sometimes, cardiac ablation may be performed as part of a different scheduled surgical procedure involving the heart.