Where Is the Culprit Lesion?

A 67-year-old man who had experienced a previous heart attack 6 years ago now presents with severe constrictive chest pain for >2 hours with profuse sweating and low blood pressure. An ECG is recorded (Figure 1), and immediately after, the cardiac catheterization laboratory is activated. No prior ECGs are available. What is the diagnosis and what is the precise anatomic lesion?Figure 1. ECG recorded by the prehospital emergency service, which activated the catheterization laboratory. Please turn the page to read the diagnosis.The interpretation of the ECG is based on QRS-ST changes combined with the clinical state of the patient. The ECG changes are as follows (Figure 1).The ECG demonstrates sinus rhythm at 82 bpm with a very long QRS duration of at least 160 ms as a result of right bundle-branch block. We suspect the right bundle-branch block is probably new in the setting of acute ischemic injury, because the perfusion of the right bundle branch depends on the first septal artery, a branch of the …