To keep the heart muscle pumping as regularly as possible year in and year out, pulses are sent out by a pacemaker. These electrical activities can be recorded with electrocardiography. Their pattern provides information about heart function, rhythm and past infarctions. After 70 years of life, the heart has contracted and relaxed about 3 billion times to pump about 7,000 liters of blood through the body every day. In order to perform this task, the sinus node in a healthy person generates a stimulus 60 to 70 times per minute at rest. This stimulus spreads as an electric current along specific pathways to the heart muscles and stimulates them to pump. The sinus node is a network of specialized heart muscle cells in the right atrium of the heart and controls the heartbeat rate, thus serving as a natural pacemaker. The heart thus constantly motivates itself to work.
The ECG – how does it work?
Since the human body conducts electricity, this excitation propagation in the heart can be recorded in a waveform. To do this, several metal plates are attached to the surface of the body as electrodes at specific intervals, and the voltage fluctuations (electrical potentials) between them are derived. They are amplified in the ECG device and displayed or printed out on the monitor. Since the electrical impulse changes direction as it progresses, the waveform (electrocardiogram) also varies depending on the timing of the action. The entire resulting sequence repeats itself with each heartbeat. Tissue changes, such as those that occur after a heart attack, cause the currents to be diverted and thus lead to typical deviations.
What at best looks like line drawings of mountains and valleys to the layman gives the expert valuable information about the heart’s action. In addition to the rhythm, i.e. the frequency and regularity of the voltage changes, their magnitude, direction and duration are also evaluated. In this way, disturbances in excitation formation, propagation, and regression in the excitation conduction system and in the heart muscles can be determined, and the position of the heart in the chest can be determined.
