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P wave detection in the Cardiospy holter system
What is a „P” wave?
The P wave is a summation wave generated by the depolarization front as it transits the atria. Normally the right atrium depolarizes slightly earlier than left atrium since the depolarization wave originates in the sinoatrial node, in the high right atrium and then travels to and through the left atrium. The depolarization front is carried through the atria along semi-specialized conduction pathways including Bachmann's bundle
resulting in uniform shaped waves. Depolarization originating elsewhere in the atria (atrial ectopic) result in P waves with a different morphology from normal.
The importance of P wave detection
Nowadays the role of P wave detection has increased in ECG Holter technology. The better amplitude resolution and higher processing speeds allow us to perform reliable P wave analysis in 24-hour or longer records. The presence or absence of the P wave from the QRS is important information in detecting Atrio-Ventricular (AV) blocks to increase the reliability of Atrial Fibrillation detection, but it is also important to
know the change in P wave morphology, for example, when determining the cause of Supraventricular Tachycardia.
By detecting AV blocks, life-threatening disturbances can be detected and assisted in deciding whether or not the implantation of pacemaker is needed.
What is atrial fibrillation (AF)?
Atrial fibrillation is the most common heart rhythm disturbance. AF is an irregular or "racing" heartbeat that can cause blood to collect in the heart and form a clot, which can then travel to the brain and cause a stroke. AF has no visible symptoms. Some people with AF describe fluttering, racing or pounding feelings in their chests, while others feel dizziness, fainting or lightheadedness during an episode. AF can happen at any age, but is more common as you get older. Starting from 2 -3 % at age 45-54 , and increase to 3-7 % at age 55-70 and exceeds the 10 % above 80 years.
Therefore, AF is one of most important diseases that needs to be managed because it is a common disease in aged populations. Atrial fibrillation makes your risk of a stroke five times higher. So if you have this condition, it’s important that you get the right treatment – both to control it and to reduce your risk of stroke.
What is a stroke and it’s relation with AF ?
A stroke is a brain attack. It happens when the blood supply to part of your brain is cut off. It can be caused by a blockage in one of the blood vessels leading to the brain or by a bleed in the brain. Blood carries essential nutrients and oxygen to your brain. Without blood your brain cells can be damaged or die. AF raises a person's risk for stroke by 5X (500%) and most AF-related strokes (75%) can be prevented. AF-related strokes cause more deaths than other strokes. In fact, many people with AF (more than 70%) will die as a result of having a stroke.
What causes AF?
Some medical conditions increase your chances of developing AF. These include heart problems such as coronary heart disease, or disease of your heart’s valves. It can also be caused by other conditions including an overactive thyroid gland, high blood pressure, lung infections like pneumonia, or a blood clot in the lung
(pulmonary embolism). Drinking too much alcohol or caffeine, taking illegal drugs, such as cocaine or amphetamines, or smoking can also trigger an episode of AF.
What are the symptoms?
Palpitations (being aware of your heart beating fast), breathlessness, chest pain or fatigue are common symptoms of AF. However, some people do not have any symptoms at all and AF is often only diagnosed during a general medical check-up. The four different types of AF are:
• paroxysmal AF comes and goes – it’s not there all the time. Your heart goes back to its normal rhythm without any treatment, usually within 48 hours
• persistent AF is where you have AF episodes that last more than seven days and it is unlikely that they will stop on their own. You may need treatment to restore your normal heart rhythm
• long-standing persistent AF means you have had continuous atrial fibrillation for a year or longer
• permanent AF is there all the time. You might be diagnosed with permanent AF if you’ve had it for more than one year and treatment with cardioversion hasn’t helped.
How is AF diagnosed?
AF can be detected by a healthcare professional checking your pulse. If your pulse feels very fast and/or irregular, they may refer you for further tests to confirm whether you have AF, and if so, what type you have.
AF that comes and goes can be hard to detect. To help diagnose it, you may be asked to wear a portable ECG monitor for 24 hours or more to check how your heart works over a longer period of time.
This option is available in the Cardiospy ECG Holter system
Detection of P wave in ECG Holter technique is a complex and difficult task as these waves are very small amplitude signals. In addition to sampling the ECG signal at a high amplitude resolution, quite strong disturbances make it difficult to detect this signal.
The Cardiospy system simultaneously provides high amplitude resolution, efficient interference filtering, and reliable P wave detection.
Algorithm of diseases based on the P wave detection in the Cardiospy Holter software
Cardiospy software uses P wave analysis to detect AV blocks (AV-I, AV-II-M1, AV-II-M2, AV-III) and Atrial Fibrillation. This algorithm is developed by our colleague, Mr. László Farkas R/D manager, who has been working with digital signal processing for more than 30 years.
Technical conditions of P wave detection
To detect P waves, it needs high amplitude resolution, which is provided by the recorders of the Cardiospy system. The amplitude resolution is better than 0.6uV, which can even detect a few 10uV P waves.
Good resolution is not enough, however, because very small P waves can be covered or distorted by minor noise. The Cardiospy filter system ensures that the P waves are displayed clearly.
Validation of P wave detection
The result rate of Cardiospy algorithms is determined by testing on a reference database, thus validating the P wave detection algorithm. The reference database contains typical P wave occurrences: small and large amplitudes, mono and biphasic, narrow and wide, short and long PQ distances.
The result of the algorithm is: Se = 95.42%, Pp = 97.16%.
(Se = Sensitivity; Pp = Positive predictivity)
Validation of disease types associated with P wave detection
The Cardiospy system uses the P wave analysis to detect various AV blocks and Atrial Fibrillation. Similarly to the P wave detection, determination of the result ratio of AV blocks and Atrial Fibrillation analyses is also performed by reference to a reference database.
The reference databases consist of some of the representative records collected from MitBih (AF) database and partly by Labtech Ltd.