Dr Carl Shakespeare consultant cardiologist  
consultant cardiologist
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Conducting System

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Abnormalities of the Electrical Conducting System / Arrhythmia:

Electrical malfunction at any point within the conducting system could affect the effectiveness of the heart as a pump. Roughly, abnormalities of the electrical system can be divided into those where the heart beats too slowly (Bradycardia) or too quickly (Tachycardia).

Investigation of Arrhythmia:
Although the patient’s history may indicate an underlying cause, frequently documentation is sought by recording the arrhythmia. An ECG may provide a clue of the cause, but it is often normal if the patient is asymptomatic. The less frequent the symptomatic episodes, the harder it may be to document them. For almost daily symptoms, a 24 hour recorder may register the arrhythmia. For attacks on a weekly basis, a 7 day event recorder may catch an episode. Sometimes attacks may be less frequent, but still a cause for worry. In such instances I often give a signed note for patients to take to the Accident and Emergency Department. This ensures that a 12 lead recording can be made if the attack lasts long enough. In other cases, we can insert a small device (Reveal Device) under the skin measuring 1 cm by 3 cm that can record any electrical abnormality for up to 2 years.

Bradycardia: In many people heart rate can be slow without any symptoms. This is especially the case in those who are very fit. In the absence of symptoms of fatigue or dizziness, this does not require any treatment. However, if the initiation of the heart beat is defective, less blood will be pumped around causing fatigue and dizziness. If conduction across the atrioventricular node is defective this can have the same effect. This is referred to as either second or third degree heart block, and is quite common with advancing age. Heart block associated with symptoms is usually treated with a pacemaker.


Normally one is not aware of one’s own heart beat. When one runs to catch the bus one is aware of it beating away, but assumes it to be a normal occurrence and pays no particular attention. However if the heart starts beating fast when you would least expect it, you begin to notice it. Tachycardias can be divided into those originating in the atria (so called Supraventricular tachycardias –SVT) or those coming from the ventricles (Ventricular tachycardias). In either case, an abnormal electric circuit spreads around the heart in either a random or defined manner. Symptoms are usually experienced as palpitations. In certain people the circulation becomes less effective fast heart rates and can cause dizziness, breathlessness, and sometimes collapse.

Treatment of Arrhythmia

Depending on the type of arrhythmia, the treatments will vary. For infrequent benign disturbances, no treatment is necessary. For certain arrhythmias, a pill can sometimes be prescribed to abort an attack (so called “pill-in-a-pocket”). For more regular rhythm disturbances, prophylactic daily medication is often prescribed. In certain cases, if medication is ineffective or causes side effects, then more curative treatment by radiofrequency ablation can be used to “burn away” an abnormal electrical pathway.

supraventricular tachycardiasSupraventricular Tachycardias:
These occur when an abnormal electrical circuit starts in the atrium. Sometimes this follows a defined electrical pathway in a circus manner causing a regular fast rhythm. This can cause sudden onset of a fast regular palpitations. Attacks can last a variable length of time and stop spontaneously. One type is called Atrioventricular Re-entrant Tachycardia (AVNRT) and results due an extra piece of wiring in the atrioventricular node. Another type is called Wolf Parkinson White Syndrome, and occurs when an extra bit of wiring connects the atrium to the ventricle to cause an abnormal circuit. Treatment in the first place usually involves daily medication with anti-arrhythmic drugs to prevent attacks. Increasingly, patients with infrequent episodes are given medication to take to abort an attack (so called “pill in a pocket”). For those patients who are resistant to the effects of medication, or who develop side effects, then potentially curative treatment can be achieved by radiofrequency ablation (see later). Atrial fibrillation is a particularly common tachycardia and is considered separately in the next section.

Ventricular Tachyarrhythmia:
This can occur in many situations. Although benign types of this disturbance can occur, more dangerous types of it need to be excluded. Benign versions include “right ventricular outflow tract tachycardia”, and this can be treated with either drugs or ablation. For more dangerous types of ventricular arrhythmia, either drugs, ablation or a defibrillator (ICD) should be considered.

Implantable Cardiac Defibrillator (ICD):
This is a device a little like a pacemaker that is implanted under the skin. Wires pass from device to the heart via the veins under the collar bone. It has the function of recognising any significant dangerous ventricular arrhythmias, and treating them automatically either by pacing the heart back to normal, or electrically shocking the heart back to normal. Most patients that require these devices are those who have had a heart attack and left with a poorly functioning heart (so called heart failure. In some cases it is patients who have structural abnormalities of the heart (cardiomyopathy) who are at risk of arrhythmias who warrant the device. Occasionally, patients with a family history of collapses who are thought to have genetically acquired the same condition (e.g Long QT syndrome, Brugada syndrome) may warrant the device.

Prior to any consideration of an ICD implant, a series of tests are undertaken to risk assess the patient. If the risk is considered significant, then implantation is considered appropriate.

Once the device is implanted (usually under local anaesthetic as a day case), it is tested to ensure that it can recognise abnormalities. Subsequently, the device is checked on a regular basis to make sure it continues to recognise abnormalities.