What is an arrhythmia?
A cardiac arrhythmia is the medical term for an irregular heartbeat or abnormal heart rhythm.
There are essentially two main things that can go wrong with the heart: the plumbing and the electrics. Many of us are keenly aware of the heart’s plumbing problems, yet we remain largely unaware of the electrical faults that cause an arrhythmia. Arrhythmias can occur in the upper chambers of the heart, (atria), or in the lower chambers of the heart, (ventricles). Arrhythmias may occur at any age. Some are barely perceptible, whereas others can be more dramatic and can even lead to sudden cardiac death.
Despite a wide range of rhythm disorders and consequences, all arrhythmias have two main causes:
- Pacemaker problems: when the heart’s natural pacemaker (the SA node) fails, or is overcome by the generation of rogue pulses from non-pacemaker cells
- Conduction problems: where the path of an electrical pulse is blocked or where the electrical signal somehow circles back to stimulate a second pulse instead of naturally ending. Called re-entry, this often happens as the result of a conduction block
Some arrhythmias have no symptoms; while others are dramatically debilitating. The following are relatively common arrhythmia symptoms:
- Premature beats, palpitations or skipped beats
Many people have arrhythmias that are undetected or misdiagnosed. For example, syncope (or fainting) in many patients is indicative of a potentially fatal heart rhythm problem. A lack of awareness of syncope in the medical community means that it often goes unrecognised or, worse, misdiagnosed as epilepsy. Atrial fibrillation, the most common heart rhythm disorder, is often intermittent. This can make it difficult for a clinician to confirm a diagnosis.
Correct diagnosis is obtained in a number of ways. An electrocardiogram (ECG or EKG) diagnoses arrhythmias by recording the timing of atrial and ventricular contractions. A Holter monitor is a device that can record 24 hours of ECG signals and an event monitor can record up to about 30 days. For arrhythmias that occur less frequently, an insertable loop recorder can be implanted under the skin of the chest to record heart activity for more than a year. A simple exercise test on a treadmill may be used in order to provoke an arrhythmia, whereas a tilt-table test might be used to induce fainting. An electrophysiological study (EP study) can also be done to manually stimulate the heart to induce fast heart rhythms, which may be an indication that the patient is prone to dangerous arrhythmias
Slow heart rhythm disorders can be treated with medications that help improve the transmission of impulses through the conduction system. A more common way is with a cardiac pacemaker; a tiny implantable device that is placed just beneath the skin in the upper chest. Small wires (leads) connect the device to the inside of the heart where it provides support if the heart beats too slowly on its own.
For the more dangerous fast heartbeat disorders (tachycardias) such as ventricular tachycardia (150-250bpm) or the potentially lethal ventricular fibrillation (250+bpm) – anti-arrhythmic drugs and other medications are used, but recent clinical trials have shown that a small device called an implantable cardioverter-defibrillator (ICD) is the most effective treatment for these arrhythmias. These are slightly larger than a pacemaker, but implanted in much the same way. An ICD monitors the heart and provides electrical pulses or shocks to slow down a heart that begins to race out of control.