EKG changes in a pulmonary embolism

definition

In the course of a pulmonary embolism, one or more pulmonary arteries are relocated. Pulmonary embolism is often caused by a thrombus that is found in the leg or pelvic veins or the inferior vena cava (Inferior vena cava) and got through the right heart into the lungs. The (partial) closure of the pulmonary arteries changes the pressure that the right heart has to work against. This is often shown in the electrocardiogram (EKG) based on certain changes.

You can find further information under our topics:

• Pulmonary embolism
• Prevention of pulmonary embolism
• Treatment of pulmonary embolism

Changes and signs

The changes in the ECG can help the attending physician make the diagnosis of pulmonary embolism. The changes are not always meaningful on their own. On the one hand, the sensitivity must be viewed critically, because only some of the patients with pulmonary embolism also show changes in the ECG. On the other hand, the abnormalities in the EKG that show up in a pulmonary embolism can also be caused by other diseases. So the specificity is not particularly great either. However, together with the clinical symptoms and the laboratory of a pulmonary embolism, the treating doctor can make a meaningful diagnosis.

At the appropriate clinic, an EKG, a heart ultrasound (Echocardiography), angiography (visualization of the vessels) and / or CT can be performed. The comparison with ECGs made earlier is helpful for assessing the changes in the ECG. Each person has to a certain extent an individual appearance of the EKG. Therefore, abnormalities can be better assessed by comparing them with ECGs that were made before a pulmonary embolism was suspected. If the abnormalities were not there before, the probability is significantly higher that they are caused by a pulmonary embolism.

The changes that can occur are rarely complete. There are usually different combinations that the attending physician must recognize. It is important to note that many of the signs are often only seen 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. Over a period of several days, the changes are only slight or not at all.

Effects of right heart strain

One of the typical changes is the appearance of an S1-Q3 type. Here, Q-waves occur in the III. Derivative and emphasized S-waves in the 1st derivative. A rotation of the heart axis as a result of the right heart load can be read off from this. Furthermore, there are arrhythmias in the sense of atrial fibrillation or (supra) ventricular extrasystoles (additional points of excitation in the heart). This is also caused by overloading the right heart. A large number of patients also have sinus tachycardia - an increase in heart rate over 90 beats per minute. The increase in the P wave is an additional sign of hypertrophy (overgrowth) and pressure load on the right heart.

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Effects of right bundle branch block

Different degrees of right bundle branch blocks (transmission of the excitation is blocked) appear as a result of the pressure load in the right heart. In the right heart, the electrical excitation is passed on via the so-called right tawara limb. In the event of acute or chronic pressure load, this leg is damaged. In the ECG this is shown as a complete or incomplete block. With a complete block, the QRS complex is widened beyond 120 ms. In leads V1 - V3, which are above the right heart, there are further abnormalities. Often the upper transhipment point (OUP) is delayed. This is the point at which the slope of the QRS complex is most negative.

The R-waves are pointed in these three leads. In the course of the damage to the right heart muscle, there is a lowering of the ST segment - this is a sign of insufficient blood flow to the myocardium. The T-wave flattening or negation is also a sign of damage to the heart muscle.

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Change of location type

The position type describes the position of the heart in the chest and in which direction the excitation primarily spreads. The sinus node is located in the right atrium, at the mouth of the superior vena cava. This is where the heart rhythm develops from around 60-80 beats. From here the electrical excitation spreads through the heart. Depending on how the heart is in the chest; So whether the apex of the heart points downwards (caudally) or to the left, the main axis of excitation is also different. The sum of all the excitation spreads ultimately gives the appearance of the EKG.

In the normal state, the axis of cardiac excitation points from top right to bottom left. The right heart stress changes the direction. The heart axis rotates 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, this is represented by the S1-Q3 type for the doctor. In other cases, the position type changes in the direction of the steep or (over-turned) right type. The heart axis rotates primarily in the frontal plane - so it does not point out of the body. Here, too, the rotation is due to the right heart load.
In the steep type, the apex of the heart points downwards. In the right type, the electrical heart axis rotates so that the excitation no longer spreads from right to left. In adults, this is a sign of a right heart strain. In children, a right type can be normal (physiological).

What is a S1Q3 type?

The EKG 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 waves) stands for the excitation of the ventricles, the T wave provides information about the regression of the ventricular excitation. The S1Q3 type is a pathological (abnormal) change in the EKG. The S wave in the first derivative (S1) and the Q wave in the third derivative (Q3) are changed. This S1Q3 configuration can occur in a pulmonary embolism on the ECG. Other possible causes are increased right heart strain or high blood pressure in the lungs.

Can you have a pulmonary embolism even if nothing is visible in the EKG?

In principle, a pulmonary embolism can also be present if nothing can be seen in the ECG. In most cases, the ECG is only used as a supplement to diagnose pulmonary embolism. Clinical symptoms, laboratory tests, and imaging are critical to the diagnosis. The following applies to the ECG: the smaller the pulmonary embolism, the fewer the signs. It can be assumed that large pulmonary embolisms show a pathological (diseased) finding in the EKG. However, smaller embolisms in particular do not initially have a major impact on hemodynamics (= blood flow) in the lungs. They therefore show little or no effects on the heart and are therefore not recognizable in the ECG.

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causes

The causes of the changes in the electrocardiogram lie in the changes in pulmonary arterial pressure (blood pressure in the arteries of the lungs). The physiological (normal) mean blood pressure (mean of systolic and diastolic pressure) is approx. 13 mmHg. Pulmonary arterial pressure can rise to 40 mmHg in patients with pulmonary embolism. This increase in pressure is not limited to the arteries of the lungs, but continues back to the heart. This is because the right ventricle does not have to work against a pressure of 13 mmHg, but against twice and three times the normal pressure. The right heart is overloaded and tries to compensate for this by changes in its structure. The right ventricle (right heart chamber) dilates, which means that its interior becomes larger. This gives the heart more power for a short time to pump against the increased pressure. One speaks here of a Cor pulmonale. This dilatation leads to changes in the EKG.

Furthermore, the increased night-time load (the increased pulmonary artery resistance) leads to a lower ejection volume from the heart. Due to the pulmonary embolism, there is ultimately insufficient oxygenation of the blood in the lungs - that is, the blood is enriched with oxygen. This leads to systemic (i.e. all organs) hypoxia (lack of oxygen), which also affects the heart muscle (the Myocardium) concerns. This under-supply of the myocardium leads to further changes in the EKG.