**1.4.2 Chest X-ray**

According to the PISAPED study, occlusion of the hilar artery, oligaemia, wedge shaped infiltration against the pleural wall is detectable in 15-45% of all cases (Miniati, Prediletto, Formichi, Marini, Di Ricco, Tonelli, Allescia & Pistolesi, 1999b). In acute PE the typical X-ray signs can be weak or absent, but a single-sided elevation of the diaphragm, stripe-like atelectasis and the oedema of the affected pulmonary tissue (Westermark-sign) may develop with the prominence of the pulmonary artery. Occasionally unilateral pleural effusion is present. Chest X-ray is useful to exclude certain diagnoses.

#### **1.4.3 Electrocardiography (ECG)**

The most common alterations are: sinus tachycardia, S1Q3T3 waveform (McGinn-White syndrome), acute P-pulmonale, negative T waves in V1-3 leads, incomplete or complete right bundle branch block, signs of RV strain, acute atrial fibrillation, atrio-ventricular conduction failures. Enlarged SISIISIII waveform develops after the dilatation of the right cavities causing the rotation of the cardiac axis. ECG signs are positive only in 50% of all patients (Torbicki et al., 2000; Torbicki et al., 2008; Geibel et al., 2005; Rodger, Makropoulos, et al., 2000).
