Is it possible to have a pulmonary embolism even if nothing is visible on the ECG?
In principle, a pulmonary embolism can also be present if nothing is visible in the ECG. In most cases, the ECG is only used as a supplement when diagnosing pulmonary embolism. The clinical symptoms, laboratory values and imaging are decisive for the diagnosis.
The following applies to the ECG: the smaller the pulmonary embolism, the less the signs. It can be assumed that large pulmonary embolisms show a pathological (abnormal) finding in the ECG. However, smaller embolisms in particular do not initially have a major influence on the hemodynamics (= blood flow) in the lungs. They therefore show no or only minor effects on the heart and are therefore not detectable in the ECG.
Causes
The causes of the changes in the electrocardiogram are changes in pulmonary arterial pressure (blood pressure in the arteries of the lung). The physiological (normal) mean blood pressure (mean of systolic and diastolic pressure) is about 13 mmHg. In patients with pulmonary embolism, pulmo-arterial pressure can rise to 40 mmHg.
This pressure increase is not limited to the arteries of the lung but continues back to the heart. This is due to the fact that the right ventricle now has to work against a pressure of 13 mmHg rather than against 13 mmHg, which is double or triple the normal pressure. The right heart is overloaded by this and tries to compensate by changes in its structure.
The right ventricle (right ventricle) dilates, which means that its interior space becomes larger. This gives the heart more power to pump against the increased pressure. This is also called a cor pulmonale.
This dilatation leads to changes in the ECG. Furthermore, the increase in night load (the increased pulmonary artery resistance) results in a lower ejection volume of the heart. The pulmonary embolism ultimately results in insufficient oxygenation of the blood in the lungs – i.e. the enrichment of the blood with oxygen.
This leads to systemic (i.e. affecting all organs) hypoxia (lack of oxygen), which also affects the heart muscle (the myocardium). This reduced supply to the myocardium leads to further changes in the ECG.
