Diagnostics of the electrocardiogram

Due to the precisely defined excitation formation and regression, deviations of the individual waves and intervals can be very specifically attributed to malfunctions. By observing the individual P-waves, their regularity and frequency, conclusions about the heart rhythm are possible.A normative sinus rhythm is present if the P-waves are regular and positive in derivation II and III, the PP intervals are regular and each P-wave is followed by a QRS complex. The normal heart rate in adults is between 60 and 100 bpm.

A higher heart rate is known as tachycardia, slower frequencies than normal as bradycardia. Blockages in the transition from atrium to ventricle are indicated by prolonged PQ intervals or absence of QRS complexes. If the PQ time is abnormally extended, an AV block is present; if each P wave is followed by a QRS complex, the transition is delayed.

This means that the excitation from atrium to chamber is prolonged, but still occurs regularly at each excitation. This corresponds to an AV block I° (atrio-ventricular block; atrium = atrium, ventricle = chamber). If a QRS complex no longer follows each P-wave, this is referred to as AV block II°.

This block is again divided into 2 types: Several atrial excitations can be blocked one after the other. The most dangerous type is the AV-Block III°. In this case, the excitation transmission from atrium to chamber is completely absent.

This means that the P-wave is no longer followed by a QRS complex. A further heart function is then only possible if a replacement system is formed by the heart. This is shown by independently occurring P-waves and QRS complexes.

By assessing the ventricular complex or the regression of excitation, conclusions can be drawn about signs of ischemia (insufficient oxygen or nutrient supply) or electrolyte disorders. If the ST- interval > 0.2 mV on the anterior wall in two adjacent leads becomes positive, the medical term is ST- elevation myocardial infarction (STEMI), i.e. a heart attack, a reduced oxygen supply in a certain area of the heart muscle. However, heart attacks are also possible without the ST elevation (Non- STEMI = NSTEMI).

Angina pectoris manifests itself by a lowering of the ST segment. Electrolyte disorders, especially changes in potassium, such as hypokalemia, can be manifested by the formation of a further wave following the T-wave (so-called U-wave). It is a sign of delayed excitation regression.

Hyperkalemia is characterized by an increased T-wave and a broadened QRS complex. A zero line (permanent isoelectric line) occurs when there is no potential difference between two derivation points. It is a sign of asystole (cardiovascular arrest).

Excitation conduction disorders can be assessed by looking at the baseline: In addition to assessing the excitation of the heart, the electrocardiogram can also be used to determine the type of position of the heart. On the one hand, this indicates the position of the heart in the chest, on the other hand, it also indicates individual thickenings of the wall, for example due to additional stress or inflammation. The position is determined by the course of the excitation from the base of the heart to the apex and can be determined with the help of the Cabrera circle.

While a steep or left-handed type is physiological, a right-handed type may be an indication of pulmonary embolism due to the increased acute stress. Thus, the position type allows the assessment of the size and position of the heart in the thorax and can be an indication of serious heart disease. Another way of examining the heart is the so-called swallow echo, in which an ultrasound probe is swallowed and the proximity of the esophagus to the heart allows the functioning of the heart to be assessed.

Type 1 (Type- Wenckebach) means that the distance between the P-wave and the QRS complex increases with each excitation until the transition stops completely. After that, the period starts again.
Type 2 (type Mobitz) leads to a sudden blockade of the Vorhofer excitation to the chamber without having extended the interval before.
Atrial flutter is indicated by a typical sawtooth-like pattern of the baseline,
Atrial fibrillation shows a slight sawtooth-like pattern of the baseline. The QRS complexes are random and not rhythmic, the P-wave is missing.