Electrocardiograph (ECG or EKG [from the German Elektrokardiogramm]) is a transthoracic interpretation of the electrical activity of the heart over time captured and externally recorded by skin electrodes. It is a noninvasive recording produced by an electrocardiographic device. The etymology of the word is derived from the Greek electro, because it is related to electrical activity, cardio, Greek for heart, and graph, a Greek root meaning "to write". In English speaking countries, medical professionals often write EKG (the abbreviation for the German word elektrokardiogramm) in order to avoid confusion with EEG.
The ECG works mostly by detecting and amplifying the tiny electrical changes on the skin that are caused when the heart muscle "depolarizes" during each heart beat. At rest, each heart muscle cell has a charge across its outer wall, or cell membrane. Reducing this charge towards zero is called de-polarization, which activates the mechanisms in the cell that cause it to contract. During each heartbeat a healthy heart will have an orderly progression of a wave of depolarisation that is triggered by the cells in the sinoatrial node, spreads out through the atrium, passes through "intrinsic conduction pathways" and then spreads all over the ventricles. This is detected as tiny rises and falls in the voltage between two electrodes placed either side of the heart which is displayed as a wavy line either on a screen or on paper. This display indicates the overall rhythm of the heart and weaknesses in different parts of the heart muscle.
Usually more than 2 electrodes are used and they can be combined into a number of pairs (For example: Left arm (LA), right arm (RA) and left leg (LL) electrodes form the three pairs LA+RA, LA+LL, and RA+LL). The output from each pair is known as a lead. Each lead is said to look at the heart from a different angle. Different types of ECGs can be referred to by the number of leads that are recorded, for example 3-lead, 5-lead or 12-lead ECGs (sometimes simply "a 12-lead"). A 12-lead ECG is one in which 12 different electrical signals are recorded at approximately the same time and will often be used as a one-off recording of an ECG, traditionally printed out as a paper copy. 3- and 5-lead ECGs tend to be monitored continuously and viewed only on the screen of an appropriate monitoring device, for example during an operation or whilst being transported in an ambulance. There may or may not be any permanent record of a 3- or 5-lead ECG, depending on the equipment used.
It is the best way to measure and diagnose abnormal rhythms of the heart, particularly abnormal rhythms caused by damage to the conductive tissue that carries electrical signals, or abnormal rhythms caused by electrolyte imbalances. In a myocardial infarction (MI), the ECG can identify if the heart muscle has been damaged in specific areas, though not all areas of the heart are covered. The ECG cannot reliably measure the pumping ability of the heart, for which ultrasound-based (echocardiography) or nuclear medicine tests are used. It is possible to be in cardiac arrest with a normal ECG signal (a condition known as pulseless electrical activity). Read More
Heart With No Beat Offers Hope Of New Lease On Life
The search for the perfect artificial heart seems never-ending. After decades of trial and error, surgeons remain stymied in their quest for a machine that does not wear out, break down or cause clots and infections. But Dr. Billy Cohn and Dr. Bud Frazier at the Texas Heart Institute say they have developed a machine that could avoid all that with simple whirling rotors — which means people may soon get a heart that has no beat.
Inside the institute's animal research laboratory is an 8-month-old calf with a soft brown coat named Abigail. Cohn and Frazier removed Abigail's heart and replaced it with two centrifugal pumps. "If you listened to her chest with a stethoscope, you wouldn't hear a heartbeat," says Cohn. "If you examined her arteries, there's no pulse. If you hooked her up to an EKG, she'd be flat-lined."
The pumps spin Abigail's blood and move it through her body. "By every metric we have to analyze patients, she's not living," Cohn says. "But here you can see she's a vigorous, happy, playful calf licking my hand." Read More