Introduction

An increased heart rate above the normal resting range, originating from the sinus node, is termed sinus tachycardia (ST). Elevated heart rate may be a usual response to activities like exercise or stress. Still, if it persists over an extended period of time or happens for no apparent cause, it may represent a medical concern. ST is one of the most common forms of arrhythmia.¹

Normal heart rate lies between 60-100 heartbeats per minute (bpm). The sympathetic and parasympathetic nervous system controls the heartbeat in the human body. However, several other factors are also involved in the heart rate change. Heart rate varies with age infants possess a heart rate of 110-150 bpm, which gradually slows down to the normal 60-100 bpm by the age of six. Similarly, it is seen to decline further in the elderly. Many underlying health issues and fitness levels also affect the heart rate.¹

Our goal in this article is to better understand sinus tachycardia. We will examine the causes, classification, symptoms, diagnosis, and treatment options. We will also go into managing sinus tachycardia, which includes prescription medications and other medical procedures.

Importance of understanding sinus tachycardia

Sinus tachycardia is generally a physiological response asking for a greater cardiac response (i.e., the body needs the heart to beat faster). It is usually a response to some kind of external or internal stimulus.

When there is a physical or psychological trigger (like exercise, stress or fear), it can have a positive physiological effect by raising catecholamine levels, decreasing parasympathetic tone, or increasing sympathetic activation. These changes help by enhancing your vision, reflexes, endurance, and strength. They can also have an impact when your body is under stress or when you need to think or act fast. If you are injured, these benefits can also hasten the healing process of any injuries your body may sustain.^2,3,4

Some other factors that can increase the heart rate and lead to sinus tachycardia are as follows:

• Sudden withdrawal of medications such as beta blockers
• Chronic pulmonary diseases 
• Hyperthyroidism
• Sleep deprivation
• Pain
• Pulmonary embolism
• Anaemia
• Hypotension and shock
• Fever
• Volume depletion (Hypovolemia)
• Sepsis
• Hypoxia
• Myocardial infarction (heart attack) and acute coronary ischemia 
• Anxiety
• Pheochromocytoma
• Decompensated heart failure
• Exposure to stimulants (nicotine), anticholinergic drugs and illicit drugs

A brief overview of the heart's electrical system

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To understand tachycardia, and by extension sinus tachycardia, it is essential to understand the heart’s electrical system. The heart consists of two upper chambers and two lower chambers. The natural pacemaker, also known as the Sinus node (present in the atrium of the heart) empowers the heart with its rhythm. This node sends electrical signals to the atria, resulting in the contraction of the heart muscles and sending blood to the ventricles of the heart.

The electrical signals that originated at the sinus node now arrive at the atrioventricular (AV) node present in the ventricles. The signals ease down here, allowing the blood to be filled within the ventricles. Lastly, when the ventricles receive the electrical signals, they pump the blood to pass it on to the lungs and different parts of the body.

This mechanism takes place 60-100 times per minute in an average heart and is termed the heart rate. Any stress in the cardiovascular system leads to an increase in cardiac output, resulting in tachycardia. 

Classification of sinus tachycardia

Either an internal or external stimulus can trigger sinus tachycardia. However, age, geographic location, underlying health conditions, physical state, and mental state also show different variations in heart rate. The increase in heart rate is caused by the parasympathetic inhibition or activation of the sympathetic system.^2,5 

Physiological sinus tachycardia

Generally caused due to exercise, anxiety, pregnancy, caffeine, and other types of physiological triggers.

Pathological sinus tachycardia

This type of sinus tachycardia is due to pathological disorders such as dehydration, hypoglycaemia, smoking, alcohol, anaemia, heart failure, trauma, drugs, pulmonary embolism, dietary biogenic amines, and mast cell disorders.

Inappropriate sinus tachycardia (IST)

This is also called Chronic Nonparoxysmal Sinus Tachycardia. The underlying cause remains undefined in this case. However, it is not related or connected to any heart disorder or any other causes like fever, etc. Inappropriate Sinus Tachycardia is a resting heart rate with beats greater than 100 per minute in addition to symptomatic palpitations. Even the most minimal movement elevates the heart rate, and the underlying, exact diagnosis remains unknown. It shows autonomic dysfunction and autoimmune dysregulation.⁶

Symptoms of sinus tachycardia

Sinus tachycardia may involve several symptoms, but the most important assessment is to determine the frequency of the symptom and the duration of it. This gives a clear idea about the intensity and guides towards the assessment and treatment of the condition.^4,5

Common symptoms include:

• Lightheadedness
• Dizziness
• Palpitations
• Weakness 
• Anxiety 
• Fatigue
• Pain 

Special attention should be given to all the medications being taken by the patients that can directly increase the heart rate. Drugs indirectly affecting the heart rate include diuretics, which initially cause hypotension and depletion (loss of essential nutrients and/or fluids), leading to an increase in heart rate. Such drugs should be monitored after the first onset of increased heartbeat.

Diagnosis of sinus tachycardia

The assessment of sinus tachycardia requires thorough observation, including a detailed patient history, evaluating the heart rate's response to medications, identifying any underlying medical conditions, and monitoring vital signs. A physical examination should include checking the heart rate, temperature, and blood pressure, as well as assessing symptoms like dizziness and weakness. These observations can be made using a variety of techniques.^4,5

• Electrocardiogram (ECG or EKG): ECG involves attaching electrodes to the chest and carefully measuring the complete heart rhythm. The electrical phases of the heart are carefully monitored, and the timings are recorded to establish how the heart functions. This is one of the most used methods for studying heart rhythm and provides a detailed picture of all electrical activity.
• Holter Monitor and Event Recorder: A Holter monitor is a portable ECG device that records your heart activity for 24 hours. It is generally worn to assess heart activity during your daily routine. It is also used to check the duration of the episodes (change in heart rate) and how many times the episodes have occurred. It gives the healthcare provider a clear picture of the heart rate. An event recorder, on the other hand, is worn for 30 days or more and the patient is asked to press a button as soon as the symptoms appear to record it.
• Echocardiogram: Unlike the ECG, the echocardiogram uses echo-sound waves to understand the rhythm of the heart. The sound waves quickly detect any cardiac muscle, flow and valve abnormality.
• Cardiac MRI: A Cardiac MRI (Magnetic Resonance Imaging) provides images or moving images of the blood flow of the heart.
• Stress test: The heart’s activity is monitored while performing a stress test, such as riding a stationary bicycle or moving on the treadmill. In certain cases, a medicine is given that stimulates the heart rate in the same way as exercise does. This helps the healthcare professional understand the heartbeat under stressful conditions.
• Tilt table test: The patient is asked to lie down on a table, and the table is tilted in a way that moves the body to a standing position. The heart rate along with the nervous system stimulation is monitored. Hence, this test gives a brief understanding of how the body acts to a shift in position.
• Electrophysiological testing and mapping: This procedure detects faults in the heart's electrical system and pinpoints their exact locations. Catheters with electrodes are inserted through blood vessels and guided to the heart. Once the catheters are correctly positioned, the heart's electrical activity is recorded and mapped. This enables the physician to observe the heart's functioning in detail and make a precise diagnosis.
• Blood and additional tests: Computerised tomography scans (CT scans) and coronary angiograms are performed with the addition of blood tests to analyse the underlying reasons.

Treatment and management

Lifestyle modifications

A healthy heart is a gift to the body. If you have been diagnosed with sinus tachycardia, following your prescribed medication regimen and taking care of your body is essential. Maintaining a healthy lifestyle can help manage your condition and reduce the potential risk of heart-related issues. Consider the following tips:

• Eat a Healthy Diet: Focus on nutritious foods and avoid those that aren't beneficial for your heart
• Restrict Alcohol: Limit alcohol intake as it can affect your heart rate
• Get Adequate Sleep: Ensure you get enough restful sleep each night
• Regular Exercise: Engage in regular physical activity to keep your heart strong and healthy

Medications and medical interventions

In cases of sinus tachycardia, it is always advised to treat the underlying conditions causing the increased heart rate. Addressing these underlying issues often helps to normalise the heart rate. If the underlying conditions cannot be identified or managed, the following interventions may be considered:

• Pacemaker placement
• Open heart surgery
• Catheter ablation
• Cox maze procedure

Summary

Sinus tachycardia is a condition where the heart beats faster than normal, usually over 100 beats per minute, due to the natural pacemaker of the heart (the sinus node) sending out signals too quickly. This can happen because of exercise, stress, fever, or other reasons like anxiety or dehydration. While it's usually a normal response to these triggers, sometimes it can occur without an obvious cause, which might need medical attention. Symptoms can include feeling your heart race, shortness of breath, dizziness, or feeling lightheaded. Treatment often involves addressing the underlying cause, such as stress or dehydration, but in some cases, medication might be needed to help slow the heart rate. The heart is central to overall health, and it's important to pay attention to any unusual activity or discomfort. If you notice symptoms like a racing heart, dizziness, or shortness of breath, it's wise to visit a healthcare provider for a check-up. Consulting with a heart specialist can ensure that everything is functioning properly and help address any concerns you may have.