What is the most appropriate diagnostic investigation for a man presenting with dyspnoea and left basal chest pain, alongside other significant symptoms?

The most appropriate diagnostic investigation for a man presenting with dyspnoea and left basal chest pain, particularly in the context of the symptoms described, is CT pulmonary angiography. This investigation is crucial in evaluating potential pulmonary embolism (PE), especially when there is acute dyspnoea and chest pain involved, as these symptoms are classic presentations of PE.

CT pulmonary angiography provides direct visualization of the pulmonary arteries and is highly sensitive and specific for detecting thromboembolic disease. It can confirm or rule out the presence of clots in the pulmonary circulation, which could explain the acute onset of dyspnoea and chest pain.

While other options might have their place in different clinical scenarios, they do not address the immediate need to evaluate for potentially life-threatening conditions such as a pulmonary embolism. D-dimer testing, for instance, can help assess the likelihood of a thrombotic event but is not definitive, and its elevation can occur in various other conditions. Echocardiography is useful for assessing cardiac function and structure but is not the primary tool for diagnosing pulmonary embolism. An ultrasound scan of the lower limbs and pelvis is valuable for detecting deep vein thrombosis, but it does not provide direct evidence of PE and would potentially delay necessary