6.1 Medical background

The heart rhythm as detected by an ECG is the result of the conduction system which is used by the heart tocoordinate the heart beat. The electrical impulse is started by the SA node at the top of the heart. At this point the conductionsystem of the heart passes the impulse across both atria (top chambers of the heart) and to the AV node. The AV node acts as atime delay and then passes the impulse on to the conduction system in the Ventricles (lower chambers of the heart). The ventricles arelarger than the atria because they actually pump the blood out of the heart and to the lungs or the rest of the body. Due to theirlarger size their depolarization produces the largest deflection on the ECG reading. This large deflection is referred to as theventricular complex or the QRS complex. After the heart is done contracting the tissue must repolarize so that it will be ready tocontract again. This repolarization shows up on the monitor as the "T" wave, or the final wave after the large QRS complex.

The two lethal rhythms mentioned earlier, V-Tach and V-Fib, both cause death by interfering with the standardelectrical coordination of the heart.

• V-Tach is a rhythm characterized by a very rapid succession of ventricular complexes. In this rhythm the heart beats at a ratebetween 100 and 250 beats per minute. On the monitor you will see the QRS complex, but due to the fast rate of the rhythm there is noflat period for effective repolarization. This rhythm is so fast in fact that the Ventricles will begin to contract before they havehad time to actually fill with blood. This is called Pulseless Ventricular Tachycardia. Once a patient has gone into PulselessVentricular Tachycardia, they have only a manner of minutes before the drop to asystole and their chances of survival plummet.
• V-Fib occurs when the electrical system of the heart becomes exceedingly discoordinated. It is characterized only by randomelectrical activity without the presence of a pulse. If this rhythm is present immediate defibrillation is needed.

If either of these rhythms is left untreated they will rapidly degenerate to asystole or flatline. In asystolethe electrical activity of the heart has stopped and defibrillation is no longer capable of restarting it. At this point the only hopefor survival is aggressive pharmaceutical action through Advanced Cardiac Life Support algorithms, but even these methods are oftenineffective.

In addition to identifying cardiac rhythms that present the possibility of death within the next few minutes,signal analysis could also identify potentially life threatening conditions before they reach a state of cardiac arrest. AcuteMyocardial Infarctions (AMIs) or Heart Attacks are among the top causes of death in the United States. While many people becomeaware of their AMI through clinical signs such as chest pain, other conditions such as Diabetes or pain from other illnesses may maskthe presence of an AMI. In the hospital an AMI can be detected through its effect on the conduction system of the heart as shownby an ECG. An active AMI will result in a lack of Oxygen to some of the myocardium. The ischemic tissue has different conductiveproperties; as a result of these changes the T-wave of a patient suffering from Ischemia in the Myocardium will be inverted. Bydetecting this rhythm we would allow patients to be alerted of their problem before they have reached a state of fullarrest.

With the increasing use of electrocardiograms and the application of devices such as defibrillators, propermeasurement and identification of ECG signals is extremely important. However with such signals on the order of microvolts,significant levels of noise corruption make this very difficult. Having proper filters to remove such noise and allow for propersignal identification is crucial. This project aims to apply filtering algorithms in hopes of identifying some of the mostcommon types of ECG signals.

In addition to V-Tach and V-Fib the program identifies the following rhythms:

• Sinus is the normal rhythm found, 60 to 100 BPM with a flat period between QRS complexes for repolarization.
• Inverted T-wave is a normal sinus rhythm were the final wave after the QRS complex has inverted in polarity, this condition isindicative of a lack of Oxygen to the heart as caused by a heart attack.
• Asystole - is a lack of electrical activity shown by a flatline on the ECG readout.