heartTarang™ is a Wireless ECG system that is being introduced as a product by Sosaley. A low powered wireless transmitter, connected to electrodes, sends data to a mobile phone, or the cloud. On the mobile phone, an advanced application delivers the results in ways that doctors and healthcare workers understand. The doctor can create a session for each patient and view the ECG tests results for instant decision. The device has an option of 3, 5, and 12 lead sensing. Other heart-related parameters will also be available.
One of the great strides Sosaley made was to deliver ECG waves that are 100% accurate and dependable. To do this, we had to design a special filter that would weed out the noise in the electrical signal. To do this properly, we first had to understand what constitutes an ECG wave and what constitutes noise, and then design and implement the noise filter.
We will explain these below.
Introduction to ECG
The electrocardiogram (ECG or EKG) is a tool that is used to measure the health of the human heart. It measures the electrical and muscular functions of the heart and gives the examiner and the doctor a quick look at how your heart is functioning. While the ECG test is simple enough, interpretation of the results needs a good eye and thorough knowledge of the heart’s functioning.
The Heart is a Pump
The heart is a pump that works in two stages through four chambers – the left and right atrium(s), and the left and right ventricles. An electrical impulse is created in the upper chambers (left and right atria). This causes the atria to squeeze and push blood into the ventricles. When the ventricles are filled with blood, they are squeezed to push blood to the body and the lungs.
Electrocardiogram (ECG/EKG) waves are indicators of the electrical activity of the heart. A healthy heart generates a regular waveform that is recognized as being consistent in terms of form and time. Any deviation from the usual and regular form and time period can be associated with a problem in the functioning of the heart.
How is Electricity Generated?
The heart has a group of cells called the sinoatrial node that is present in the right atrium of the heart. The main role of the sinoatrial node is to create an action potential (an electrical charge) that is used for squeezing of the chambers. The action potential is a change in the voltage across the membrane of the cells that are generated by the movement of the charged ions.
The group of cells that constitute the sinoatrial node can act independently of the human brain.
The proper functioning of the sinoatrial node signifies a healthy heart. When the node becomes defective, the rhythms become abnormal – too slow or too fast.
Blockages of the blood supply into or out of the heart and particularly to the sinoatrial node can cause ischemia and cell death in the sinoatrial node. This will cause the electrical function of the sinoatrial node to malfunction. These are usually because of myocardial infarction or progressive coronary artery disease.
Understanding ECG Signals
As I said before, though it is easy to conduct an ECG test, understanding and interpreting the ECG signals is not easy. Let us look at the aspects (or parts) of the waveform that a clinical analyst and doctor have to understand.
- P-Wave, PR Interval, and PR Segment
This is the first part of the heart’s pumping action. The P-wave shows the start of the action potential of sinoatrial node called atrial depolarization. The PR interval is the time between the start of the action potential to the next activation – that of the QRS complex.
- The QRS Complex
This represents the activation of the ventricles. Remember, this is when the ventricles get filled with blood? Though called QRS complex, an ECG may not necessarily show all the three waves. The QRS duration is the time between the start and end of the QRS complex. A short duration of <0.12 seconds represents a healthy heart.
- The J point and the ST Segment
The ST segment represents the plateau phase of the action potential. This part of the wave has to be studied carefully as it changes rapidly in a wide range of conditions. The ST segment starts at the J point and ends somewhere between S and T. Myocardial Ischemia causes deviation of the ST segment. Deviation could be suppression or elevation of the ST segment that is measured as the difference in height between the J point and PR segment.
- The T-Wave
The heart has two major types of cardiac muscle cells. The myocardial conducting cells and myocardial contractile cells. The myocardial conducting cells initiate and propagate the action potential and act as the conduction system of the heart. The contractile cells conduct electrical impulses and create the contractions that pump blood. Contractile cells constitute nearly 99% of the charge conducting cells in the atria and ventricles.
The T-wave shows the re-polarization of these cells. Again, changes occur in a wide range of conditions. In general, the transition from the ST segment to the T-wave should be smooth.
- The U-Wave
The U-wave is a positive wave occurring after the T-wave. This is seen frequently in leads V2-V4. People with slow heart rates display U-waves more often. The exact nature of the U-wave and its importance is still not understood fully.
- QT Duration and QTc Interval
The QT duration represents the total length of the ventricular depolarization and repolarization. It starts with the beginning of the QRS complex and ends with the completion of the T-wave. The QT duration is inversely related to the heartbeat and thus has to be corrected based on the heart rate. The corrected QT duration is referred to as QTc interval.