Which of the following is LEAST useful in investigating the above complication?

b. Fibrin degradation products (D-dimer) is a test useful only in the process of ruling out a pulmonary embolus. A negative result predicts a high likelihood of absence of pulmonary embolus; a positive result is almost meaningless diagnostically. D-dimers are expected to rise post-operatively and thus should not form the first line of investigation for a suspected pulmonary embolus. Arterial blood gases and electrocardiography are invaluable for the investigation of dyspnoea for both quantifying the respiratory compromise and in stratifying the differential to either cardiac or respiratory causes. Chest radiographs may demonstrate pneumonic processes or pneumothoraces and form part of the standard investigation of breathlessness. CT-PA forms the most definitive imaging in cases of suspected pulmonary embolus but may return equivocal results in the presence of pre-existing lung pathology