SVT vs Sinus Tachycardia ECG

Heart rate is the number of times a heart beats. An adult, resting heart beats 60-100 per minute. It varies for children and adults while doing work or resting. Tachycardia is an increased heart rate. Supraventricular tachycardia (SVT) and sinus tachycardia are two common types of tachycardia.

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Exercise, stress, or fever are normal physiological responses that cause sinus tachycardia. SVT is an abnormal condition in which the heart beats more than 150 beats per minute. It is due to an abnormal electrical conduction pathway above the ventricles.

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Both can be misdiagnosed as the other. SVT for sinus tachycardia or vice versa, causing inappropriate treatment and complications. Let us read more about the features of SVT and sinus tachycardia on an ECG in this blog.

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Dangerous Heart Rate

Not all fast heart rates are dangerous, as some are temporary and caused by various factors.

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They can be classified into:

• multifocal atrial.

• ventricular.  

• sinus.

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The maximum possible heart rate in sinus tachycardia

To calculate the maximum heart rate possible during exercise following methods can be used.

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• HRmax is equal to 220 - age in years.

• HRmax is equal to 208 – (.7 X age in years).

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Sinus tachycardia in infants is 220/ minute and <180 /min in adults.

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Tachycardia: Heart Risk and Complications

An increased heart rate over a long time affects the cardiovascular system. When the heart beats too quickly, it does not get enough time to fill with blood between contractions. It leads to decreased cardiac output and causes symptoms. Untreated tachycardia causes complications such as heart failure, stroke, or sudden cardiac arrest.

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• ‍Tachycardia complications: When the heart works harder than it should, it causes changes in the heart structure, like thickening of the muscles and heart wall, or development of scar tissue. These changes affect the heart’s ability to pump blood and increase the risk of heart failure or other diseases.

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Sinus Tachycardia

When electrical signals start from the heart's sino-atrial node (the heart’s natural pacemaker). And the heart beats faster than normal, it is sinus tachycardia. 

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Causes

• Anxiety or stress.

• Heavy caffeine consumption.

• Heavy alcohol consumption.

• Electrolyte imbalance.

• Anaemia.

• Hormonal problems.

• Fever.

• Strenuous exercise or physical activity.

• Side effects of medication.

• Cigarette smoking.

• Consumption of drugs like cocaine.

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Symptoms

Most symptoms are short-lived and often not even noted by people.

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• Fast heartbeat.

• Palpitations.

• Chest pain.

• Lightheadedness.

• Difficulty breathing.

• Dizziness.

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Supraventricular Tachycardia SVT

It is caused by abnormal electrical circuits in the heart that make it beat faster than normal. The heart's electrical system begins at the sinoatrial node, the natural pacemaker. Signals travel through the atria to the atrioventricular node and then to the ventricles. It ensures a coordinated and regular heartbeat.

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Causes

In SVT, extra pathways or faulty signals develop above the ventricles, either in the atria or within the AV node. It causes electrical impulses to loop repeatedly and beat faster than usual. They are caused in the following ways.

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• AV node reentrant tachycardia (AVNRT): Involves a short circuit within the AV node.

• AV reentrant tachycardia (AVRT): Has an extra connection between the atria and ventricles, such as in Wolf-Parkinson-White syndrome.

• Atrial tachycardia: Begins from a single spot in the atria and overrides the normal pacemaker.

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SVT episodes may have an underlying cause or may be congenital and can be triggered by stress.

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• Caffeine.

• Alcohol.

• certain medications.

• exercise.

• hormonal changes.

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Symptoms

Symptoms of supraventricular tachycardia are:

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• Pounding or fluttering in the chest is called palpitations.

• A pounding sensation in the neck.

• Fainting.

• Chest pain.

• Shortness of breath.

• Sweating.

• Weakness or tiredness.

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Sinus Tachycardia vs SVT: Distinguishing Features

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Medical history: SVT vs Sinus tachycardia

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ECG characteristics of Sinus tachycardia

• Heart Rate: Sinus tachycardia is a heart rate of more than 100 beats per minute. It occurs due to exercise, anxiety, or fever.

• Heart rate variability: It is variable.

• P wave: The P wave is consistent and is upright in lead II. It indicates that atrial depolarisation occurs from the sinus node.

• PR interval: The PR interval is within the normal range of 120 to 200 milliseconds. The consistency indicates that electrical impulses originate in the sinus node.

• QRS complex: The QRS complex is normal in appearance in the last 120 milliseconds. The narrow QRS indicates that ventricular depolarization occurs through a normal conduction pathway.

• P Wave Axis (0-75°): The P wave axis is normal, ranging from 0 to 75 degrees. It indicates a normal atrial depolarisation suggestive of sinus tachycardia, ensuring that the rhythm is sinus in origin.

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ECG characteristics of Supraventricular tachycardia

1. Heart rate: In supraventricular tachycardia, the heart rate ranges from 60 to 200 beats per minute. A rapid heart rate is caused by abnormal electrical pathways above the ventricles that create short circuits.

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2. Heart rate variability: It is not.

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3. P-wave: The P wave is absent or hidden within the T wave before it. This variability indicates that atrial depolarization is not from the sinus node.

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4. PR Interval: The PR interval in SVT is short or variable, reflecting rapid conduction through the atria or in an aberrant pathway.

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5. QRS complex: The QRS complex is narrow, less than 120 milliseconds. It indicates normal ventricular conduction.

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6. P wave axis: It is abnormal and exceeds 75 degrees, which indicates atrial depolarisation due to an altered electrical pathway. Supraventricular tachycardia should be distinguished from other tachyarrhythmias also such as atrial fibrillation, atrial flutter, and ventricular tachycardia.

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• Atrial fibrillation has an irregular rhythm and absent P waves.

• Atrial flutter has a saw-tooth pattern in the inferior leads.

• Ventricular tachycardia has a wide QRS complex and occurs in patients with structural heart disease.

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Treatment

The treatment aims to terminate a rapid heart rate. SVT is treated using the following.

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• Vagal manoeuvres such as carotid sinus massage or the Valsalva manoeuvre help to restore the normal sinus rhythm. It is a non-invasive technique that stimulates the vagus nerve. It reduces the heart rate by increasing parasympathetic tone.

• Adenosine is administered intravenously, and it blocks atrioventricular node conduction temporarily, resetting the normal rhythm.

• Calcium channel blockers slow the heart rate and conduction of Impulses through the AV node.

• Beta-blockers prevent recurrent episodes.

• Cardiac ablation is a minimally invasive procedure used to treat SVT when no other methods work to correct the heart rate. Cardiac ablation improves patients’ quality of life. The technique destroys or isolates abnormal electrical pathways, causing the tachycardia.

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In sinus tachycardia, the cause rather than the arrhythmia is treated. Lifestyle modifications, such as reducing caffeine, managing stress, and treating underlying conditions like fever or anaemia, help control it.

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Conclusion 

Both conditions involve elevated heart rates with different underlying mechanisms and ECG characteristics. Being able to distinguish between the two entities makes management and treatment possible. Gauze steps in to help you differentiate and improve the long-term results for your patient.