Electrocardiography (ECG) is a useful adjunct to other pulmonary tests because it provides information about the right side of the heart and therefore pulmonary disorders such as chronic pulmonary hypertension and pulmonary embolism.
(See also Electrocardiography Electrocardiography The standard electrocardiogram (ECG) provides 12 different vector views of the heart’s electrical activity as reflected by electrical potential differences between positive and negative electrodes... read more in cardiovascular disorders.)
Chronic pulmonary hypertension Pulmonary Hypertension Pulmonary hypertension is increased pressure in the pulmonary circulation. It has many secondary causes; some cases are idiopathic. In pulmonary hypertension, pulmonary vessels may become constricted... read more leading to chronic right atrial and ventricular hypertrophy and dilation may manifest as P waves of higher amplitude (P pulmonale) and ST-segment depression in leads II, III, and aVF; rightward shift in QRS axis; inferior shift of the P wave vector; and decreased progression of R waves in precordial leads.
Chronic obstructive pulmonary disease (COPD) Chronic Obstructive Pulmonary Disease (COPD) Chronic obstructive pulmonary disease (COPD) is airflow limitation caused by an inflammatory response to inhaled toxins, often cigarette smoke. Alpha-1 antitrypsin deficiency and various occupational... read more 
patients commonly have low voltage due to interposition of hyperexpanded lungs between the heart and ECG electrodes.
Pulmonary embolism Pulmonary Embolism (PE) Pulmonary embolism (PE) is the occlusion of pulmonary arteries by thrombi that originate elsewhere, typically in the large veins of the legs or pelvis. Risk factors for pulmonary embolism are... read more 
(submassive or massive) may cause acute right ventricle overload or failure, which manifests classically (but not commonly) as right axis deviation (R > S in V1), with S-wave deepening in lead I, Q-wave deepening in lead III, and ST-segment elevation and T-wave inversion in lead III and the precordial leads (S1Q3T3 pattern). Right bundle branch block also sometimes occurs. Sinus tachycardia is the most common ECG finding in pulmonary embolism.
