An electrocardiograph is a device used for detecting changes of electrical potential (“electrical activity”) caused by heart activity. The record of these changes is called an electrocardiogram (ECG). The changes of heart electrical activity are responsible for mechanical (“spontaneous”) and coordinated contractions of every single part of the heart. Electrical impulses are created in the heart in so called sinoatrial (SA) node, which is found in the rear part of right atrium. From here, electrical impulses advance through the wall between right and left atrium to so called atrioventricular node, placed on the base (see picture 4, upper part) of the interventricular wall (it is the wall between the right and left ventricles). From here, electrical impulses spread through the bundle of His to Tawara´s branches and Purkinje fibers, which lead the electrical impulse to the entire heart muscle of ventricles. This electrical impulse (so called depolarisation of the heart muscle) leads to coordinated and optimal contraction of both atriums and afterwards even the ventricles (see picture 4).

Picture 4: Electrical conduction (author: Icewalker)

The electrocardiograph records this electrical heart activity and transfers it to the form of an ECG curve, which is separated into several waves and sections (segments):

Picture 5: ECG curve (author:  Agateller – Anthony Atkielski)

In reality, an ECG record looks like this (see picture 6):

Picture6: Normal ECG curve (author: Bionerd)

The first part of the ECG curve is a record of electrical potentials (“electrical heart activity) recorded from the extremities (leads I – III and aVR, aVL and aVF) and the second part is the record from leads on the chest (leads V1 – V6), see picture 7.

Picture 7: ECG leads (authors: Medic a Adnav)

During myocarditis, there are a lot of different changes on the ECG curve. None of them is completely typical for myocarditis. ECG findings of patients with myocarditis are highly variable. Sometimes, physicians observe ECG curves changes, which are also observed during heart attack or pericarditis (inflammation of pericardium – outer heart wrap).

The most typical ECG changes at patients with myocarditis are illustrated in the following ECG records.

During the disease, different ECG changes are observed. One of the most typical findings are so called negative (or inversed) T waves. This means that T waves are recorded on the ECG curve in the inverse position when compared to a usual record (see picture 8 and compare with picture 5 and 6).

Picture 8: ECG curve – T waves (author: Ped. Clinic FN Motol)

Other ECG changes observed during myocarditis are so called elevation or depression of ST segment (see picture 9 and 10).

Picture 9: ECG curve – ST elevation (auttor: Ped. Clinic FN Motol)

Usually, the wave S should be “deeper” than the Q wave. At the same time, the ST segment should be on the same level as the PQ segment. In the case of the ST elevation, ST segment is “raised” above the PQ segment.

Picture 10: ST elevation (author: Bron 766)

In the case of ST depression, this segment is by contrast under the level of the PQ segment. During myocarditis also tachycardia (accelerated heart rhythm even in rest) may be observed. The pulse can be periodic, but also even non-periodic. Also different types of extrasystoles (“extra” electrical impulses – e.g. of QRS complex – see picture 5) may be recorded. They can be created in the atrium and/or in ventricles. Further, atrioventricular (AV) blocks may be observed. It means that some electrical impulses from the heart atrium are not led “right” through the AV node or the bundle of His to ventricles (see picture 4).

In some cases, this disorder can show lower in the heart ventricles in the form of a block of Tawara´s branches. Sometimes, even changes of QRS complex are observed in the form of widened QRS complex. Physicians can also find some changes of the PQ complex and the Q wave or other sights that some changes in the function or structure of the heart has happened (e.g. “thicker” heart muscle).

Generally, it could be said that the ECG curve does not diagnose myocarditis, but it is a part of the diagnosis and it records the course and potential complication of the disease like arrhythmias, symptoms of pericarditis etc.

The ECG record does not distinguish the severity of heart muscle damage, but it helps with the diagnosis and during subsequent monitoring.

Some types of arrhythmias can persist even after myocarditis itself, but mostly they disappeared without any treatment.

Author of the opening picture: Agateller – Anthony Atkielski