Heart Rhythm Problems
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The Normal Heart »
Schematic of the heart outlining the normal electrical conduction system. Electrical activation originates in the sinus node (SA) spreading throughout the right and left atria (RA & LA). There is a layer of insulation between the atria and the right and left ventricles (RV & LV). The wavefront of electrical activation must therefore pass through the AV node to enter the ventricles, where it spreads through specialised electrical pathways (in yellow) to activate the ventricles. Normal rhythm is otherwise known as sinus rhythm (originating in the sinus node).
The heart is a muscular pump responsible for circulating blood around the body, usually pumping at a rate of 60-80 beats per minute. It has an electrical system that controls the heart rate and also co-ordinates the activity of the 4 cardiac chambers (Left Atrium, Right Atrium, Left Ventricle, Right Ventricle) so that they work efficiently together.
In the normal heart the sinus (SA) node acts as the body’s pacemaker and initiates each heart beat. The normal heart rhythm is called sinus rhythm. A wave of electrical activation spreads from the SA node throughout the atria causing them to contract and supply blood to the ventricles. The AV node acts as a junction box between the atria and ventricles allowing each wavefront of electrical activation to pass into the ventricles at a controlled rate. The wave of electricity then passes throughout the ventricles, which pump blood around the body once activated. The AV node is normally the only electrical connection between the atria and the ventricles.
Fast Heart Beat/Palpitations »
At rest your heart should beat 60 to 100 times per minute and for the majority of the time we are completely unaware of this routine beating. However, when we exercise it is quite normal for our heart rate to increase above 100 beats per minute and when asleep it is not uncommon for our heart rate to fall below 60 beats per minute.
We generally use the term of palpitation to describe an awareness that the heart is beating, be it too fast or slow, irregular and just appearing stronger than is usual.
During your consultation with your Specialist, he will ask a number of questions to diagnose what your 'palpitation' may be. He may need to perform an ECG or further tests, such as fitting an external monitor to be worn for anything from 24 hours to one week, in order to pinpoint your diagnosis. This monitoring may be referred to as Holter monitoring and is a patient activated recorder during symptoms to help diagnose the nature or your palpitation.
If heart rate exceeds 100 beats per minute then the term tachycardia may be used.
Tachycardia which starts gradually with exercise, strong emotions or due to a high temperature during illness is quite normal. An overactive thyroid can also cause tachycardia so your GP may have already organised a blood test to check your thyroid function.
In many cases awareness of palpitation does not require any specific treatment and the reassurance from your Specialist may be all that is needed.
However some tachycardias are inappropriate and it may be that the patient has developed an abnormal rhythm. Frequently these abnormal rhythms arise from the heart’s upper chambers.. Common examples include atrial fibrillation, atrial flutter and SVT.
The most common arrhythmia is atrial fibrillation (AF). The Bristol Heart Rhythm Centre is run by the South West’s leading AF specialists and the condition is described in detail under the Atrial Fibrillation (AF) heading (see below).
Slow Heart Beat »
Your heart should normally beat between 50 and 70 times a minute when at rest; although it can be slower if you have achieved a high level of fitness or taking certain medications such as beta-blockers. Your heart rate should rise with exercise; however the maximum rate varies from person to person.
The speed at which the heart beats is determined by its own internal pacemaker which is known as the sinoatrial node and is located in the right atrium. With every heart beat electricity spreads from the sinoatrial node across the atria. The electricity reaches the main pumping chambers of the heart, (known as the ventricles) by passing through the atrioventricular node.
A slow heart beat can occur either because of a problem with the sinoatrial node which is sometimes referred to as sick sinus syndrome or because electricity gets held up or blocked in the atrioventricular node and this is known as heart block.
A slow heart beat may cause no symptoms or may cause dizzy spells, blackouts, breathlessness or tiredness.
Treatment of excessively slow heart beats may include review and modification of the dose of any drugs that slow the heart beat and may involve a minor surgical procedure to fit a pacemaker.
Atrial Fibrillation (AF) »
Atrial Fibrillation is the most common arrhythmia in the UK affecting 1-2% of the population. It becomes more common as we age and is present in 5-10% of those aged over 80.
Schematic of a heart in atrial fibrillation. Four pulmonary veins (PV) drain into the left atrium. Abnormal electrical activity spreading from these veins throughout the left atrium drives atrial fibrillation. In this diagram the left upper pulmonary vein is driving AF, however any or all of the four veins may be involved.
In atrial fibrillation, the sinus node is no longer regulating the electrical activation of the atria. Instead, chaotic, swirling wavefronts of electrical activation pass through the atria. The drivers of this rhythm often arise in the pulmonary veins that drain blood from the lungs and plumb into the back of the left atrium. Hence, AF normally originates in the left atrium.
During AF the atria are not activated regularly or uniformly. As a result, the atria do not pump efficiently. Instead they fibrillate or ‘wobble’, resulting in stagnant blood flow within the atria, reduced blood flow from the atria to the ventricles and a chaotic irregular pulse.
Reduced flow during AF may dispose to formation of blood clots in the left atrium of susceptible patients, in turn giving rise to a risk of stroke. Not all patients are at risk of stroke, and the risk may be significantly reduced through thinning of the blood with drugs such as warfarin.
Reduced flow also reduces the pumping efficiency of the heart. This can make people breathless and fatigued. The irregular and often fast heartbeat during atrial fibrillation may also cause uncomfortable palpitations.
AF is described as paroxysmal if it is episodic and self-terminates spontaneously. It is persistent if the patient’s heart is in atrial fibrillation continuously. Treatments may differ according to this distinction.
Treatment for atrial fibrillation
Two main areas must be covered when treating AF:
1) Stroke risk.
Those at risk of stroke should have their blood thinned (anti-coagulated) with medications such as warfarin. To assess your stroke risk use the stroke risk calculator on the following link: http://www.arrhythmiaalliance.org.uk
Symptoms resulting from AF may be improved through either controlling the heart rate (usually with medications) or by restoration of the normal heart rhythm (either medication, electrical cardioversion or catheter ablation).
Most people using this name refer to a particular common arrhythmia called typical atrial flutter. In this arrhythmia an abnormal electrical circuit exists around one of the heart valves in the right side of the heart - the tricuspid valve. Commonly this arrhythmia can be diagnosed using a standard ECG. Patients may be unaware that they have this arrhythmia. Alternatively, symptoms may include palpitations, shortness of breath and lethargy. The mainstay of treatment of atrial flutter is catheter ablation. This daycase procedure is normally straightforward and curative. Similarly to atrial fibrillation, thinning of the blood with warfarin should be also considered on a case by case basis.
Supraventricular tachycardia (SVT) »
The term SVT may be used to describe any fast heart rhythm originating in the top chambers of the heart (atria) - link to arrhythmia alliance PDF). SVTs may arise in any age group and often have a benign prognosis - although can be very troublesome and in rare circumstances dangerous. Three main groups are recognised including AVRT, AVNRT and atrial tachycardia.
AVRT. An abnormal electrical circuit exists allowing electrical activation to rapidly circulate via the AV node and the Accessory pathway (AP) that connects the atria and the ventricle. APs are redundant and ablation of the AP prevents recurrence of the arrhythmia.
1. AVRT arises in people born with an extra electrical pathway between the top and bottom chambers of the heart. Instead of a single electrical connection (the AV node), there are two connections allowing a faulty electrical circuit to develop between the atria and the ventricles. The extra electrical pathways are often called ‘accessory pathways’. The accessory pathways behave differently in different people. In some cases criteria are met for the diagnosis of Wolff-Parkinson-White syndrome (WPW). Very rarely life-threatening arrhythmias may occur in patients with WPW.
Catheter ablation to destroy the accessory pathway is curative and usually achieved with few major complications.
AVNRT. This arrhythmia occurs when people are born with two electrical inputs into the AV node. This allows a faulty electrical circuit to develop resulting in fast heart rhythms (SVT). Ablation of one limb of the faulty electrical circuit allows normal conduction to return over the remaining electrical pathway.
2. AVNRT is not dangerous. It arises when there are two electrical pathways into the AV node rather than the usual single route. A faulty electrical circuit can arise as in AVRT (see above). Catheter ablation of one of the two extra pathways is curative.
Atrial Tachycardia. This arrhythmia arises when over-excitable cells fire off rapid electrical signals driving the heart to beat quickly. Ablation of the faulty area prevents further arrhythmia.
3. Atrial tachycardias normally result from overactive atrial cells that fire off rapidly driving fast heart rhythms. In some people atrial tachycardias settle with tablets however catheter ablation may once again prove curative.
Some patients are not troubled by their SVT and can manage with simple tricks that return their hearts to normal rhythm (link to arrhythmia alliance PDF). Others have episodes more often, find their symptoms more troublesome and need medical input. Treatment options include tablet therapy or catheter ablation. Many patients prefer not to take tablets in the longterm and opt for a catheter ablation procedure as it has high success rates, low risks and offers the potential to cure them of their complaint.
Ventricular Tachycardia »
Ventricular tachycardia (VT) refers to a fast heart beat that originates within the ventricles (lower chambers of the heart). VT may be dangerous and is sometimes associated with an increased mortality risk in some subgroups of patients (e.g in patients who have had large heart attacks). In other patients VT has a benign prognosis. Patients must be assessed individually to assess their symptoms and risk due to the VT.
Symptoms include collapse, blackout, dizziness, chest pain, palpitations. There is a risk of sudden death associated with some VTs. VT circuits tend to originate in and around areas of scar. Hence VT is most commonly seen in patients with a history of heart attack or coronary artery disease. The most common benign VTs include Right Ventricular Outflow Tract tachycardia (RVOT VT), and Fascicular VT.
Treatment options include medical therapy and catheter ablation. Both approaches may work.
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