How to calculate Heart Rate from ECG

ECG signals provide valuable information about the heart's rate and function. The heart rate is a parameter derived from an ECG, a critical cardiovascular health indicator. Calculating heart rate from ECG is a skill required in various medical and healthcare applications. The heart rate is measured in beats per minute, bpm, and is calculated by analyzing the interval between successive heartbeats.

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A healthy heart rate is between 60 and 100 beats per minute, essential for overall body functions. A proper heart rate ensures oxygen and nutrients are delivered throughout the body while waste like carbon dioxide is removed. Heart rate changes are sometimes regular and are called physiological changes. On the other side, they may signal issues known as pathological issues.

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A heart rate could indicate fitness or a rhythm problem. It helps doctors determine if variations in heart rate are healthy or need attention. An ECG allows a healthcare professional to calculate heart rate and determine if the variations in the heart are normal or not.

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What is ECG?

A standard ECG has 12 leads between the chest and the limbs. The limb leads measure the heart's electrical activity from the arms and legs. Offering insight into the heart’s function from different angles. The chest leads placed across the front of the chest capture electrical signals directly from the heart.

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Together, these leads give a detailed, comprehensive view of the heart's electrical activity and overall health. They are V1 – V6. The limb leads measure the heart's electrical activity from the limbs, arms, and legs. There are six limb leads.

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Understanding the Rhythm Strip

Paper speed  

Paper output speed is the rate at which the ECG machine produces a tracing

The standard output is 25 mm /second.

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When the standard paper speed is 25 mm per second.

1 small square (1 mm )= 0.04 seconds or 40 milliseconds.

5 Small squares (5mm) = 1large square =0.02secs (200 ms)

5 large squares = 1 second

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At the standard paper speed of 25 mm/ second, the rhythm strip consists of

               250 small squares = 50 large squares = 10 seconds.

Rhythm Strip is recorded for one minute

                Therefore, 1500 small squares =  300 large squares = 1minute

Heart Rate and ECG

Manual method of calculating heart rate

The pulse rate is the number of times our heart beats per minute. It is also known as the heart rate.  A normal resting heart rate should be 60 to 100 beats per minute though it can vary from minute to minute. Age and general health also affect the pulse rate, so it is important to remember a normal pulse can vary from person to person.

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Calculating heart rate from the ECG

Any of the following three methods can be used to calculate the heart rate on the ECG.

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Large square method

Recall from above 300 large squares.= 1 minute at paper speed 25 mm per second.

Divide 300 by the number of large squares between each RR interval (space between 2 consecutive R waves = 1 beat ).

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Small square method

1500 is divided by a number of small squares between consecutive R waves.

This method is used for fast heart rates.

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R wave method

Heart rate = Number of R waves on rhythm strip x 6

The number of complexes R waves on the rhythm strip gives the average rate over 10 seconds. When this is multiplied by 6, We get average beats per minute(10 secs X 6= 1 minute).

It is useful in slow and irregular heartbeats.

Automatic heart rate calculation by ECG machines

Automatic ECG machines can compute heart rate from the signals. This method is quick and accurate but may be unreliable if QRS and T morphology are abnormal. Always verify machine results by manual calculations.

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Heart Rate

A resting heart rate is an indicator of fitness in general health. In adults, a lower heart rate translates to a high degree of fitness and a low incidence of cardiac events. Trained athletes have a resting heart rate as low as 40.

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It is because the heart muscles are stronger and can pump blood more efficiently. Conversely, a higher rate is associated with cardiovascular diseases and premature death.

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Adults

• Normal. 50 - 100 beats per minute.

• Tachycardia > 100 beats per minute.

• Bradycardia <  50 beats per minute.

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Children

• Newborn 110.-150 bpm.

• 2 years 85 -125 bpm.

• 4 years 75 - 115 bpm.

• 6 years 60 -100 bpm. 

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Bradycardia (Slow heart rate)

A heart rate of less than 60 beats per minute.

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• Physiological causes-Athletes have resting bradycardia due to enhanced cardiac efficiency.

• Pathological causes. Heart blocks, Hypothyroidism, Beta blocker medication.

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Tachycardia (Fast heart rate)

• Heart rate exceeds 100 bpm

• Physiological causes Exercise, stress, fever, dehydration.

• Pathological causes: arrhythmia, atrial fibrillation, supraventricular tachycardia. Hyperthyroidism. Heart failure, Anemia.

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Tachycardia can be a normal reaction to a stressor, but if persistent and symptomatic, it needs evaluation.

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Practical Applications of Heart Rate Calculation

Calculating heart rate influences diagnosis, treatment, and management of various conditions.

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Diagnosis of Cardiac Conditions

Identifying arrhythmias: Heart rate calculation helps to detect abnormal rhythms such as atrial fibrillation, tachycardia, and bradycardia.

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Assessing Cardiac Health

Changes in resting heart rate indicate underlying heart conditions, such as heart failure or ischaemic heart disease.

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Monitoring Response to Treatment

• Medication Management: Monitoring heart rate helps to evaluate the effectiveness of prescribed drugs and allows dose adjustments.

• Post-procedure monitoring: It ensures stability and helps to take complications early after cardiac surgeries. Or pacemaker implantations

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Guiding Physical Activity and Rehabilitation

Heart rate sets a safe exercise limit for people with chronic conditions. Monitoring it during activities assesses fitness levels and detects abnormal responses, signaling possible heart problems.

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Critical Care and Emergencies

When in shock, the heart rate guides decisions on fluids, medications, and other treatments. Rapid or irregular heartbeats indicate worsening health, prompting quick action.

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Predicting Outcomes

A higher resting heart rate is linked to increased mortality. It helps assess risk in patients with heart disease, hypertension, or diabetes.

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Heart Rate Variations

Several factors can influence changes in the heart rate; some may be normal, while others may suggest underlying heart problems.

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Physiologic Variations

These variations reflect the body's adaptations to daily activities and emotional states.

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• The heart rate fluctuates naturally throughout the day. It lowers during sleep and increases during waking hours.

• Stress, anxiety, and excitement affect the heart rate. Arrhythmias indicate health issues that require evaluation.

• Physical activity increases the heart rate, and rest normalizes it.

• Breathing patterns: heart rate increases with breathing in and slows with breathing out.

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Pathological variations

Bradycardia is a slow heart rate, and tachycardia is a fast heart rate. The irregular rhythms suggest an underlying cardiovascular disease.

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• A heart rate below 60 bpm indicates a heart block or hypothyroidism.

• A heart rate faster than 100 bpm is due to atrial fibrillation, dehydration, or fever.

• Irregular heart rhythms indicate premature flutter or electrolyte imbalances.

• Variations in heart rate point to stress, autonomic dysfunction, or chronic diseases indicating a heart disease.

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Why a low heart rate is beneficial?

The heart rate lowers as the muscles become strong and get better at pumping more blood per heartbeat. The body needs a few heartbeats to pump the same amount of blood. But if the heart muscle is weak. It needs to beat more times to pump the same amount of blood.

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Common Mistakes in Heart Rate Calculation

Common mistakes in heart rate calculation that lead to inaccurate readings are counting beats, misinterpreting irregular rhythms,  improper device use, and measuring under inappropriate conditions.

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Miscounting beats

• Counting too quickly or slowly: Counting too fast or hesitating during the count can lead to missing beats or adding extra beats.

• Short measurement period: Measuring for less than 60 seconds and multiplying can amplify errors. It happens more when the rhythm is irregular.

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Incorrect use of devices

• Poor fit or placement: Loose or misaligned devices cause inaccurate readings, so all variables must be snuggly positioned.

• Movement artifacts: Minor movements can also disrupt the device's ability to measure heart rate correctly.

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Measuring under inappropriate conditions

• Measuring after activity: Counting immediately after physical activity or during stress. Gives. A higher reading. Misinterpreting the resting heart rate.

• Environmental distraction: Noisy or busy environments lead to losing focus in counting errors.

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‍Tips for accurate heart rate measurement

• Proper electrode placement reduces artifacts so that we can measure heart rate accurately.

• The skin should be cleaned for better contact and securing electrodes.

• All movements should be prevented to avoid electrode dislodgement.

• The procedure should be explained to the patient to reduce anxiety

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Conclusion

Measuring the RR interval on the ECG helps to determine the heart rate. Healthcare providers can identify arrhythmias and evaluate treatment response by determining heart rate from the ECG. It increases the diagnostic accuracy.

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Mastering this technique increases our ability to manage heart health. Gauze offers a one-stop AI-powered solution for interpreting ECG heart rate and improving clinical outcomes.