A fast heart rate is known as tachycardia and commonly defined as a heart rate greater than 100 beats per minute. Although a fast heart rate is commonly defined as a heart rate greater than 100 beats per minute, there is no specific cut off for what defines a significantly fast heart rate or a number above which a fast heart rate becomes an issue. Each case is different and needs to be approached differently. Articles on normal heart rate and low heart rate are linked here.
What Causes A Fast Heart Rate?
The heart rate can be fast for reasons inside the heart or reasons outside the heart.
The electrical system of the heart itself can cause a fast heart rate if there are ‘short circuits’ that occur within it. These are known as tachyarrhythmias. These can occur from the top chamber or the bottom chamber of the heart. Fast heart rates from the top chamber of the heart are known as supraventricular tachycardia or SVT for short. They can be regular or irregular. One of the most common causes for a fast heart rate, especially if irregular in nature is known as atrial fibrillation or AF for short. Fast heart rates that occur from the bottom chamber of the heart are known as ventricular tachycardia or VT for short. These are generally regular in nature. Ventricular Tachycardia is considered more concerning in general than other causes of fast heart rate and needs prompt work up and attention.
The heart rate may be fast simply as a reaction to other processes going on in the body. For example, if the body is under stress from pain, infection, blood loss or general illness then the heart rate may increase significantly, often to provide blood to vital organs. When someone has pain, there is an increase in secretion of stress hormones that directly increases heart rate through acting on receptors in the heart. There may be problems with hormones such as overproduction of thyroid hormone that may lead to increase in heart rate. When the body is in shock, be it for reasons from inside or outside the heart, the heart rate will increase significantly. For example if the heart function is severely impaired and the amount of blood being pumped out per beat is therefore reduced, the heart attempts to compensate by increasing the rate. Finally its important to note that ingestion of substances such as stimulants that would directly increase heart rate need to be ruled out as a cause of fast heart rate.
Symptoms of a Fast Heart Rate
Many people don’t have symptoms when they find out they have a fast heart rate. They often just notice it when checking their pulse rate, or from a blood pressure machine or a Fitbit type accessory. Some patients may feel tired, short of breath, dizzy or fatigued. If the heart rate is particularly fast people may notice a thumping sensation or palpitations. If the heart rate is particularly fast, there may be a sensation of light-headedness or feeling of faintness. In the case of SVT that comes and goes at unpredictable times, there may be intermittent palpitations and light-headedness. When the palpitations come on, some patients may have associated chest pain that on occasion can point to underlying heart artery disease. If the palpitations are more serious, people may pass out as a result.
Consequences of a Fast Heart Rate
Often a fast heart rate will have no significant effect on the heart, although there may be associated symptoms. In some cases however the symptoms may be enough as to cause concern and quality of life limiting symptoms. In a few cases, the heart rate may be continually elevated over a long period of time weeks-months often at heart rates above 120-130 beats per minutes and lead to a weakening of the heart muscle known as tachycardia mediated cardiomyopathy. Regardless, it is important to work up and identify any underlying causes of fast heat rate and give the appropriate treatment.
Fast Heart Rate – What Tests Are Needed?
History – The initial most important thing is a good history. Are there associated symptoms of palpitations, light-headedness, fatigue, and dizziness or passing out? Is there associated chest pain or shortness of breath? Is the fast heart rate intermittent or constant and do the symptoms only appear when the heart rate is elevated? What happens to the blood pressure when the heart rate is elevated? Is there a history of heart disease or prior testing? These questions are critical in determining the seriousness of the situation and determining the work up required. If there are alarm symptoms such as above then the heart rate needs work up and should not be ignored.
Physical Exam – Is the heart rate regular or irregular when it is fast. Are there physical exam signs of heart failure such as fluid retention? Also a thorough physical exam can point toward other systemic problems such a thyroid issues or other.
EKG – A baseline EKG is key. Is the heart rhythm normal or abnormal? Is there any evidence of abnormality of the heart rate or conduction system of the heart? It is particularly useful to perform an EKG during the period of fast heart rate as it may help clinch the diagnosis if there is a cardiac cause.
Blood work – Basic blood tests will be performed to rule out anemia or electrolyte abnormalities, thyroid function testing may be performed. Other testing may be performed as indicated.
Monitor – Often palpitations or fast heart rate occur intermittently and never when at the doctors office! A monitor can be worn to help catch an intermittent fast heart rate and then characterize it providing useful information. Monitors can be 1 day, several days, several weeks, or even much longer term if implanted. I personally find the utility of a monitor goes up significantly if a symptom diary is kept to record times when symptoms occur. The diary can then be crosschecked with the monitor to see any correlations.
Echocardiogram – This is an ultrasound scan of the heart that looks at the structure and function of the heart done commonly in patients with palpitations or fast heart rate.
EP study – If the heart rate elevation is felt to be from a cardiac cause, or related to abnormality of the structural system of the heart then sometimes to clarify a diagnosis electrophysiology specialists may perform an invasive test to clarify the diagnosis.
Treatment of Fast Heart Rate
Treat the Underlying Cause: Most important is to ensure there is no underlying systemic problem that is causing the fast heart rate. If there is anemia, for example, that will need to be treated. Infection and dehydration would need to be treated. Hormonal imbalances would require treating. Medications will be reviewed and any potential offending agents will need to be stopped if possible.
Medications: It is important not just to treat a number; the reason underlying must be sought out. If the fast heart rate is thought to be from a cardiac cause then the appropriate treatment should be given. If there is significant muscle dysfunction then treatment aimed at strengthening the heart is given. If there are problems with the electrical system of the heart then medicines to slow the rate may be given such a beta blockers or calcium channel blockers. In some cases stronger medicines that prevent the occurrence of the arrhythmia in the first place may be prescribed, known as anti-arrhythmic medications. Specialists known as electrophysiologists typically prescribe anti-arrhythmic medications.
Procedures: If the fast heart rate is felt to be a primary cardiac arrhythmia then procedures may be required, particularly if medications do not work. In the case of SVT, procedures known as ablation can be particularly effective. In patients with Atrial fibrillation an ablation procedure may be useful if medicines aren’t effective and symptoms are present. VT may also be treated in this manner. Ablation procedures are performed by electrophysiologists, who are cardiologists specializing in the electrical system of the heart.
Fast Heart Rate – Overview and Conclusion
A fast heart rate although often defined as a heart rate over 90 is not necessarily abnormal and each case is different. History, physical exam and diagnostic testing are required in order to determine the significance of the heart rate and to see if any treatment is required. Treatment for non-cardiac causes of fast heart rate is to address the underlying cause. In the case of cardiac causes of fast heart rate, typically medication will be tried first or in some cases a procedure required particularly if the problem is with the electrical system of the heart.