## Calculation of heart rate from ECG

###### Calculation of heart rate from ECG

In my last post I have enumerated the points for studying an ECG.

The first step is to check the calibration and paper speed. Then comes the calculation of heart rate. There are various methods of calculating the heart rate from ECG. We will discuss about the most commonly used and authentic methods of calculation.

ALL THESE METHODS ARE APPLICABLE FOR PAPER SPEED OF 25MM/SEC.

No.1 and 2 are applicable for a regular heart rhythm. No.3 is applicable for irregular heart rhythm

No.1: Calculate the number of large boxes

Count the number of large boxes between two consecutive R-R waves. 300 divided by the number of large boxes between two consecutive R-R waves is the heart rate. In figure 1 there are 3 large boxes between two consecutive R-R waves, so the heart rate is 300/3 =100/minute.

No.2: Calculate the number of small boxes

Count the number of small boxes between two consecutive R-R waves. 1500 divided by the number of small boxes between two consecutive R-R waves is the heart rate. In figure 1 there are 16 small boxes between two consecutive R-R waves, so the heart rate is 1500/16 = 94/min. This method is more accurate than the previous method.

No.3: Calculate the total number of R-waves in the rhythm strip

This method is applicable when the heart rate is irregular e.g. in patients with atrial fibrillation, frequent VPCs etc. At a paper speed of 25 mm/sec the duration of a 12-lead ECG is 10 seconds. So count the total number of R-waves in the rhythm strip (the long lead II at the bottom of the ECG ) and multiply it by 6 to get the heart rate. In the example shown below there are frequent VPCs.

The total number of R-waves is 12. So the heart rate is 12×6 = 72/min

I suggest you practice all the methods in the beginning so that after sometime you will be well habituated to use a method as needed.

Next week we will discuss about analyzing rhythm from ECG.

## Simplest approach to reading the ECG. Part-1

ECG or EKG (the electrocardiogram) has retained its role as the first and foremost investigations for many cardiovascular diseases. ECG is absolutely mandatory for diagnosis of heart rhythm and for myocardial ischemia. It has a prominent role in the diagnosis and management planning of a variety of cardiac diseases starting from heart failure and cardiomyopathy to valvular diseases and pericardial diseases.

Health care professionals are expected to be familiar with ECG. But to make sense of the variously shaped lines we need a few basic steps. Is article is part of a series of articles on ECG.

There is a systematic approach to reading the ECG. Medical students should always try to make a written report of the ECG according to the heading as listed below. Try to report as many ECGs as you get, and try to remember the systematic approach to ECG reading.

1. Speed – Paper speed is conventionally 25 mm/sec. It is normally written at the bottom of the Ecg.

2. Calibration – Vertically, the ECG graph measures the height (amplitude) of a given wave or deflection, as 10 mm (10 small boxes) equals 1 mV with standard calibration. Always check the calibration otherwise a false diagnosis of chamber enlargement or hypertrophy will be made or missed.

3. Rate

4. Rhythm

5. Axis

6. Loop (mainly in congenital heart disease)

7. P-wave

8. PR- interval

9. QRS complex

10. ST- segment

11. T-waves

12. QT- interval

13. U- Wave

14. Any other abnormal waves (like:- osborn wave, epsilon wave etc)

These 14 points when remembered and applied in the analysis of ECG will give the diagnosis in almost all cases.

We will further delineate each point in simple and clear terms in the subsequent posts.

## Coronary artery disease

Coronary artery disease

The heart like any other organ in the body needs constant supply of blood to survive. Blood reaches different parts of the heart through the coronary arteries.  Coronary arteries are of vital importance for the sustenance of life.

The different  normal functions of the coronary arteries include:

1. Carrying blood to different  parts of the heart

2. Regulating  blood supply to the heart in the face of varying blood pressure

3. Increasing blood supply to the heart in the face of increased cardiac demand like during exercise.

The coronary arterial system:  Can be divided into four parts

1. Left main coronary artery (LMCA)

Which divides into

2. Left anterior descending artery  (LAD) And

3. Left circumflex artery (LCX)

4. Right coronary artery (RCA)

What is coronary artery disease (CAD)

Any disease which involves coronary arteries is CAD. Usually the most common form is reduction in the size of the coronary arteries. Many disease conditions can result in coronary artery disease but the most common cause of CAD is atherosclerosis. Other diseases like autoimmune diseases, congenital diseases can result in CAD.

CAD occurs due to a variety of reasons, which are called risk factors. You can read more about risk factors here.

What are the types of CAD?

CAD is a septum of diseases and it is divided to two categories

1. Chronic stable angina (CSA): In CSA there is a pattern of chest discomfort associated with exertion or emotional excitability. The occurrence of angina is after a predictable amount of work.

2. Acute coronary syndromes ( ACS)

ACS are are again divided into three types

A. Unstable angina: When there is new onset angina, worsening of previous angina, rest angina, it is called unstable angina

B. Non-ST elevation myocardial infarction

C. ST elevation myocardial infarction – the classic heart attack

This classification is important for the point of view of management and the aggressiveness of treatment.

What are the symptoms of coronary artery disease?

A. Angina : Chest pain or discomfort .

B. Angina equivalents – fatigue , dyspnoea (shortness of breath) , eructations, palpitation

C. Sudden onset acute severe chest pain

D. Cold sweating

What to do?

First of all see your doctor for evaluation and treatment. Some of the general management modalities are discussed here.

Investigations

For the diagnosis of CAD the following investigations may be needed:

A. ECG – is of central importance in CAD. ECG in many occasions shows changes suggestive of reduced myocardial blood flow

B. Stress test – Different types of stress tests are available like treadmill test, nuclear stress  tests. A stress test can be done by performing exercise on a treadmill or by giving drugs in patients who are unable to do exercise. It is done when the symptoms are not typical and ECG changes are not typical.

C. Echocardiography – is for assessment of structure and function of heart

D. CT coronary angiography – It  is a noninvasive imaging modality for the diagnosis of CAD. It is like any other CT scan. Contrast injections are given to visualize the coronary arteries

E. MRI coronary angiography – Not very widely used for imaging of coronary arteries

F. Coronary angiography – this is the gold standard for the diagnosis of coronary artery disease and any percutaneous treatment for CAD can be done in the same setting

Treatment:

A. Risk factor control – Risk factor control is one of the most effective interventions for reducing the impact of coronary heart disease.  Proper control of blood pressure, diabetes, quitting smoking, treatment of abnormalities of cholesterol are some of the steps that greatly reduce the incidence and prevalence of CAD.

B. Medications- Patients with CAD will on some medications indefinitely (usually life long). For chronic stable angina, the first line of treatment is usually medical management. Even  patients who undergo coronary artery stenting or bypass surgery need to take medicines life long.

C. Coronary angiography and percutaneous coronary interventions are usually advised for patients who have more serious symptoms or for whom symptoms are not easily controlled with medicines. In presence of certain high risk factors patients should undergo early angiography and intervention or surgery

D. Coronary artery bypass grafting (CABG)

Drugs used in treatment of CAD:

1. Anti- platelets e.g. Aspirin, Clopidogrel, Prasugrel, ticagrelor, etc

2. Statins e.g. rosuvastatin, atorvastatin etc

C. Beta blockers (metoprolol, bisoprolol etc)

D. Ace inhibitors or angiotensin receptor blockers

E. Anticoagulants (heparin)

F. Nitrates

G. Nikorandil

H. Ranolazine

H. Therapies for refractory angina

Details about each class of drug I will post each week( Monday )