ECG changes in the case of a pulmonary embolism

Definition

In the course of a pulmonary embolism, one or more pulmonary arteries are displaced. Pulmonary embolism is often caused by a thrombus that has detached itself in the leg or pelvic veins or the inferior vena cava and entered the lung through the right heart. The (partial) occlusion of the pulmonary arteries changes the pressure against which the right heart must work. This is often shown in the electrocardiogram (ECG) on the basis of certain changes.

Changes and indications

The changes in the ECG can help the treating physician to diagnose pulmonary embolism. By themselves, the changes are not always meaningful. On the one hand, sensitivity must be viewed critically, since only a proportion of patients with pulmonary embolism also show changes in the ECG.

On the other hand, the abnormalities in the ECG, which are evident in pulmonary embolism, may also be caused by other diseases. The specificity is therefore not particularly high either. However, together with the clinical symptoms and the laboratory of a pulmonary embolism, the attending physician can make a meaningful diagnosis.

If the clinic is suitable, an ECG, a heart ultrasound (echocardiography), an angiography (imaging of the vessels) and/or a CT should be performed. A comparison with previously obtained ECGs is helpful for the assessment of changes in the ECG. To a certain extent, each person has an individual appearance of the ECG.

Therefore, abnormalities can be better assessed by comparing them with ECGs taken before suspicion of a pulmonary embolism. If the abnormalities were not there before, the probability that they are due to a pulmonary embolism is much higher. The changes that may occur occur completely only in rare cases.

Usually there are different combinations that the treating physician must recognize. It is important to note that many of the signs are often only visible in the first few hours after the embolism event. An ECG should therefore be taken repeatedly in the first few hours to monitor the progress of the disease.

Over a period of several days, the changes are only slight or no longer visible. One of the typical changes is the appearance of an S1-Q3 type. Q-waves appear in the III.

derivation and emphasized S-waves in the I. derivation. The result is a rotation of the heart axis as a result of right heart strain. Rhythm disturbances in the sense of atrial fibrillation or (supra-) ventricular extrasystoles (additional excitation points in the heart) are also evident.

This is also a result of overloading the right heart. The majority of patients also show sinus tachycardia – an increase in heart rate of more than 90 beats per minute. The increase in the P-wave is an additional sign of hypertrophy (excessive growth) and the pressure load on the right heart.

Differently pronounced blocks of the right thigh (transmission of excitation is blocked) appear as a result of the pressure load on the right heart. In the right heart, the electrical excitation is transmitted via the so-called right tawara leg. Acute or chronic pressure load causes damage to this leg.

In the ECG, this appears as a complete or incomplete block. A complete block results in a widening of the QRS complex beyond 120ms. In the leads V1 – V3, which are located above the right heart, further abnormalities are found.

Often the upper transition point (OUP) is delayed. This is the point at which the slope of the QRS complex is most negative. The R-spikes are sharply pronounced in these three derivatives.

In the course of the damage to the right heart muscle, a decrease in the ST segment is observed – this is here a sign of insufficient blood supply to the myocardium. The T-wave flattening or negation is also a sign of damage to the heart muscle. The position type describes the position of the heart in the chest and in which direction the excitation primarily spreads.

In the right atrium, at the mouth of the superior vena cava, lies the sinus node. This is where the heart rhythm of about 60-80 beats is generated. From here the electrical excitation spreads through the heart.

Depending on how the heart is located in the chest, i.e. whether the tip of the heart points downwards (caudally) or to the left, the main axis of excitation also lies differently.The sum of all excitation propagation finally results in the appearance of the ECG. In the normal state, the axis of the heart excitation shows from top right to bottom left. The direction changes due to the right heart load.

There is a rotation of the heart axis around the sagittal axis (from top to bottom) out of the frontal plane, so that the axis now points out of the body. In the ECG, the physician sees this as S1-Q3 type. In other cases, the position type changes towards the steep or (over-twisted) right type.

The heart axis rotates primarily in the frontal plane – i.e. it does not point out of the body. Again, the rotation is caused by the right heart strain. In the steep type, the tip of the heart points downwards.

In the right heart type, there is a rotation of the electrical axis of the heart, in which the excitation no longer spreads from right to left. In adults this is a sign of right heart strain. In children, a right heart type can be normal (physiological).

The ECG consists of several waves and spikes, which are named in alphabetical order from P to T. The P-wave shows the electrical excitation of the atria, the QRS-complex (consisting of Q-, R- and S-wave) stands for the excitation of the ventricles, the T-wave gives information about the regression of the ventricular excitation. The S1Q3 type is a pathological (abnormal) change in the ECG. The S-wave in the first lead (S1) and the Q-wave in the third lead (Q3) are altered. This S1Q3 configuration can occur in the ECG in case of a pulmonary embolism. Other possible causes include increased right heart strain or high blood pressure in the lungs.