Sinus Tachycardia ECG vs Normal ECG

Differentiating between physiological and pathological heart rate on an ECG is important as it helps determine our heart health and outcomes. Sinus tachycardia is a faster-than-usual heart rate. It occurs when we exercise, feel anxious, or are stressed, and can be due to an underlying health condition. It is usually a temporary occurrence and may not be of concern until and unless it persists even during rest.

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The sinus node is our heart's natural pacemaker. The node generates electrical impulses that move across the heart and cause it to contract. When normally conducted, these electrical impulses have a healthy sinus rhythm, which causes the heart to beat at 60 to 100 beats per minute.

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This blog compares the characteristics of the two kinds of ECGs.

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All you need to know about Tachycardia:-

By convention, a heart rate greater than hundred beats per minute is tachycardia. Sinus tachycardia is an elevated rhythm from the sinoatrial node and is most commonly a physiologic response to a physical activity like exercise.

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Sinus Tachycardia

A sinus rhythm with a resting heart rate more than 100 beats per minute in adults or above the normal for age, and general.  

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Normal heart rates in children

• Newborn: 110 to 150 bpm.

• Two years: 85 to 125 bpm.

• Four years: 75 to 115 bpm.

• Six years: 60 to 100 bpm.

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Types of tachycardia:-

1. Sinus tachycardia

It is a physiological increase in heart rate as a response to exercise, fever, stress, or anxiety. The rhythm remains regular and originates from the sinoatrial (SA) node.

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2. Atrial Fibrillation (AF or Afib)

It is the most common type of tachyarrhythmia. It occurs when multiple chaotic electric signals fire, causing them to contract ineffectively. The rhythm is irregular and can be temporary or persistent, sometimes requiring treatment to prevent complications like stroke.

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3. Atrial flutter

This rhythm is similar to Afib but more organised. The Atria beat rapidly in a regular pattern, usually around 250 to 350 beats per minute. Mild paroxysmal atrial flutter may not always need treatment, but chronic atrial flutter can sometimes become atrial fibrillation. A person may experience both arrhythmias at different times.

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4. Ventricular tachycardia (VT)

It is a life-threatening rhythm that starts in the ventricles. It can prevent the heart from filling and pumping efficiently. Sustained VT lasting for more than 30 seconds or causing symptoms can lead to cardiac arrest if not treated quickly.

5. Supraventricular tachycardia (SVT)

It includes a group of fast heart rhythms that start above the ventricles. SVT is often felt as a sudden pounding heartbeat that begins and ends abruptly. It is usually not life-threatening but can cause significant discomfort.

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6. Ventricular fibrillation (VF)

It is a medical emergency. The ventricles quiver chaotically instead of contracting, resulting in no effective blood flow. It is usually caused by severe heart disease or trauma, and if not treated immediately with a defibrillator, it can be life-threatening.

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What causes tachycardia?

Sinus tachycardia is usually a secondary condition caused by:-

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1. Non-pharmacological reasons

• Exercise.

• Pain.

• Anxiety.

• Hypovolemia.

• Hypoxia.

• Anaemia.

• Pyrexia.

• Sepsis.

• Pulmonary embolism.

• Cardiac tamponade.

• Alcohol withdrawal.

• Hyperthyroidism.

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2. Pharmacological

• Beta-agonist:  adrenaline, salbutamol, dobutamine.

• Sympathomimetics: amphetamines, cocaine, methylphenidate.

• Antimuscarinics: Antihistamines, TCAs, Carbamazepine, Atropine.

• Others: caffeine, theophylline, marijuana.

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Symptoms: How to identify tachycardia?

Often, there are no symptoms. A tachycardia is diagnosed accidentally during a physical examination for some other reason. The general symptoms include:-

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Palpitations are expressed as racing, pounding, or fluttering in the chest.

• Chest pain.

• Fainting.

• Lightheadedness.

• Rapid pulse.

• Shortness of breath.

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Normal ECG and its Characteristics:-

 When the heart beats in a regular sinus rhythm between 60 and 100 beats per minute, all the important intervals are within normal range.

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P wave

• Leads I, aVF, and V3-V6 show upright waves.

• Duration is less than or equal to 0.11 seconds.

• Leads I, II, aVF, and V4-V6 show positive polarity in the wave; V1-V3 show biphasic waves; aVR shows a negative wave.

• Waves are smooth in shape.

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PR Interval

It is between 0.12 and 0.20 seconds.

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QRS complex

• Duration < 0.12s.

• Amplitude > 0.5 mV in one standard lead and > 1.0 mV in at least one precordial lead.

• Upper limit of normal amplitude is 2.5- 3.0 mV.

• Small septal Q Waves in I, aVL, V5, and V6, with the duration less than  0.04s. The amplitude is less than one-third of the amplitude of the R Wave in the same lead.

• A positive deflection with a large upright R Wave in Leads I, II, V4-V6, and a negative deflection with a large deep S in aVR, V1, and V2.

• In general, proceeding from V-1 to V6, the P waves keep getting taller while the S waves get smaller. At V3 or V4, these waves are usually equal- it is called the transitional zone.

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ST segment

• Isoelectric segment slanting upwards, merging into the T wave in the normal ECG.

• Elevated upto 2 mm in some precordial leads.

• Never depressed by more than 0.5 mm in any lead.

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T waves

• T wave deflection should be in the same direction as the QRS complex in at least five of the six limb leads.

• Normally rounded and symmetrical, with more gradual ascent than descent.

• Upright in leads V2 to V6 and inverted in aVR.

• Amplitude of less than 0.2 mV in leads V3 and V4, and at least 0.1 mV in leads V5 and V6.

• Isolated T wave inversion is asymptomatic and is generally a normal variant.

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QT interval

Durations are normally less than or equal to 0.40 seconds for males and 0.44 seconds for females. Sinus tachycardia can be triggered by stress, anxiety, or fear. It occurs when the body requires a faster heart rate and sends signals to the SA node to increase the heart rate. When the need subsides, the heart rate slows. Speeding up and slowing down both require time and are never sudden.

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Differences Between a Normal ECG and a Sinus Tachycardia ECG

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Preventing Tachycardia

Until your heart condition is diagnosed, you can use home remedies to help slow down your heart from racing.

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1. Stimulate the vagus nerve that connects the brain to the heart. It can be done by coughing, gagging, taking a cold shower, or doing a Valsalva maneuver.

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2. Reduce stress by meditation, yoga, deep breathing, and relaxation techniques.

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3. Stay hydrated and consume foods and drinks with electrolytes.

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• Magnesium is found in  dark leafy greens and dairy products.

• Potassium in potatoes, bananas, and avocados.

• Calcium is found in dark leafy greens.

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To prevent tachycardia, adopt:-

1. Healthy lifestyle

• Do moderate intensity aerobic exercises for at least 30 minutes to enhance cardiac efficiency and lower your resting heart rate. 

• Take a balanced diet low in saturated fats, cholesterol, and sodium. Eat more fruits, vegetables, lean proteins, and whole grains.

• Sleep adequately, 6 to 7 hours, to support health.

• Avoid smoking and alcohol to improve heart health.

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2. Manage underlying conditions

• Hypertension, diabetes, and thyroid diseases need to be effectively managed.

• Hydrate your body adequately.

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3. Limit or avoid triggers

• Avoid caffeine, nicotine, and recreational drugs.

• Any work that triggers your stress and anxiety.

• Avoid overexertion.

• Be cautious in extreme cold or hot environments.

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Conclusion

Sinus tachycardia ECG and a normal ECG differ in heart rate. A normal ECG has a resting heart rate of 60 - 100 beats per minute, whereas in sinus tachycardia, it exceeds 100 beats per minute but maintains normal sinus rhythm. Sinus tachycardia indicates a physiological or pathological cause.