Overview

Tachycardia is the medical term for a fast heart beat. The heart rate is strictly controlled by a complex balance of nerves and hormones which respond to the demands of the body. Usually, the heart rate is precisely matched to the needs of the body so that a person at rest will have a low heart rate and a person doing exercise, or recovering from exercise, will have a faster heart rate. However, the systems controlling the heart rate only work when the hormones of the body are in balance, there is enough water in the body (“circulating volume”) and the heart electrics are functioning normally.

When to See a Cardiologist

It is normal to be aware of your heart rate, and for this to be faster than normal during exercise and while recovering from exercise. However, most of us are fairly in tune with what is a “normal” heart rate for us during exertion, and if the rate suddenly changes or recovers differently from usual, this may indicate a new medical problem.

It is important to distinguish whether a tachycardia is caused by the normal heart electrics going faster than usual (“sinus tachycardia”) or by abnormal electrical signals within the heart (“arrhythmia”). The language in this area is confusing and just to muddy the waters even further, a normal heart beat shows some beat-to-beat variability and this is called "“sinus arrhythmia”. Unlike all other arrhythmias, “sinus arrhythmia” is normal!

Telling the differnce between sinus tachycardia, sinus arrhythmia and other “proper” fast arrhythmias is a complex area and requires special tests. Some of the more sophisticated wearables can help with collecting data,, but even to interpret an ECG collected on an Apple Watch, say requires a cardiologist.

, In general, sinus tachycardias are either normal or due to a non-cardiac problem. Arrhythmias, on the other hand, are never normal, and are always due to a cardiac problem. Sinus tachycardia is an exception to this rule (see above).

A cardiologist will have access to tests that can tell with a high degree of confidence whether a tachycardia is sinus (i.e. a normal rhythm) or not.

Apart from sinus arrhythmia, however, the general rule is that an arrhythmia is a heart problem, but sinus tachycardia is not. n general, tachycardias caused by factors outside the heart will cause high heart rates but still in a normal rhythm (i.e. with the electrical . Tachycardias

Wearable heart rate monitors can be a useful tool to check whether feelings you have do genuinely correspond with high heart rates, but most wearables will not be able to tell you if the heart rhythm has changed.

A cardiologist can help you confirm the diagnosis and investigate for the cause of syncope. Most cases will have a cardiovascular cause, and in this case a cardiologist may be able to advise on treatments to reduce the chance of it happening again.

A cardiologist can also advise on whether you need to inform the DVLA or other bodies. The rules around driving if you suffer from syncope can be complex, and in certain circumstances you may be advised against driving until a diagnosis is made and treatment has been effective for a period of time. Ignoring these rules can be a criminal offence and may invalidate your insurance. A cardiologist can help you understand the rules in this area.

Almost all of the serious causes of syncope have their roots in heart disease. A cardiologist is the right doctor to diagnose and treat heart diseases causing syncope.

Associated Symptoms

Some cases of syncope are preceded by a long period, or “prodrome” of other symptoms, which may include:

  • Lightheadedness

  • Nausea and / or vomiting

  • Ringing or pulsation heard in the ears

  • Feeling hot, clammy or sweaty

  • Feeling anxious

  • “Tunnel vision” - the visual field becoming restricted and seeming to darken at the edges

The pre-syncope prodrome can last up to hours in some people. In general, syncope with a long prodrome is much less likely to be due to an arrhythmia (heart rhythm problem) than syncope with no prodrome at all. Syncope without a prodrome is sometimes called “unheralded syncope”.

Causes

Syncope is caused by either a sudden drop in cardiac output (the volume of blood pumped by the heart) or by a drop in vascular resistance (the “squeeze” applied by blood vessels to maintain blood pressure).

Causes of transient decreased cardiac output leading to syncope include:

  • Tachycardia - the heart flipping into an abnormal fast rhythm. The rate has to be extremely high to cause a drop in blood pressure and this usually implies a serious heart rhythm abnormality such as ventricular tachycardia. This is uncommon.

  • Bradycardia - the heart rate drops suddenly. Bradycardias are a very common cause of syncope; in young patients this is usually part of a reflex syncope complex, but in older patients bradyarrhythmias are usually caused by conduction disease.

  • Cardioversion pauses - this is when there is a temporary pause in the heart rate as the heart reverts from a tachyarrhythmia such as atrial fibrillation, back into normal “sinus” rhythm. The sinoatrial node, which drives the heart rate during sinus rhythm, can sometimes take a few seconds to wake up after a period of tachyarrhythmia. This pause can sometimes be enough to cause syncope.

Causes of a drop in vascular resistance include:

  • Orthostatic hypotension - this occurs when blood vessels fail to tighten sufficiently on moving from a sitting or lying position to standing up, leading to a drop in blood pressure. This is a very common cause of syncope and presyncope with changes in position. Most people will suffer very brief episodes of mild orthostatic hypotension under the right circumstances, for example the on standing up after bending over to tie shoelaces. Only in severe cases will orthostatic hypotension cause full syncope.

  • Reflex syncope - this complex condition is the cause of classic “fainting” for example on the sight of blood, or in a warm room after a large meal. The “reflex” involved causes a sudden drop in heart rate, blood pressure, or both, leading to sometimes prolonged and repeated syncopes. The key to diagnosing this condition is to recognising the usually classic triggers.

  • Cardiovascular autonomic dysfunction - this is a spectrum of disorders affecting the regulation of heart rate and /or blood vessel tone. Sufferers commonly complain of dizziness and presyncope, sometimes progression to syncope. The most widely recognised disorder in this cluster of related conditions is Postural Tachycardia Syndrome (PoTS) which can cause a racing heart beat and lightheadedness on position change. It is uncommon to experience complete syncope with isolated PoTS but is may be more common in other forms of autonomic dysfunction.

Treatment

Treatment of syncope depends on the cause. Clearly syncope caused by an arrhythmia will only improve with treatment of the arrhythmia. For tachycardias and cardioversion pauses this may involve drugs and ablations to suppress rapid heart rhythms. For bradycardias a pacemaker may be recommended.

Syncope related to changes in blood vessel tone may be harder to control than arrhythmic syncope. A range of treatments will be used to boost blood pressure and to reduce the drive to initiate unhelpful reflexes.

Request a call-back to discuss a consultation for syncope