The Patient: This ECG is from a 59-year-old woman who was found by the EMS crew to be unresponsive, with agonal respirations at about 6 breaths per minute. Her pulse was thready at the carotid, and absent peripherally. Her skin was pale, cool, and mottled. Her BP via the monitor is 81/40, peripheral pulses not being palpable. An initial rhythm strip showed sinus rhythm at 75 bpm with right bundle branch block and ST elevation.
The patient’s husband gave a history of “difficulty breathing” since sometime this morning, alcohol dependence, hypertension, tobacco use, and insomnia. He said she had been drinking heavily for several weeks.
She was immediately ventilated and intubated, and an intraosseous infusion line established. A12-lead ECG was done, and it showed a dramatic change in the rhythm and ST segments over the initial strip. She was transported to a nearby hospital with CPR support. She achieved return of spontaneous circulation (ROSC) at the Emergency Department, after having three doses of epinephrine. Follow up with the ED physician revealed that the patient had suffered a massive gastrointestinal bleed. This patient, due to loss of a critical amount of blood, had low blood pressure and very poor perfusion, which resulted in damage to her heart (and possibly other organs as well). I do not have further follow up, but will update this if I receive more information.
The ECG: The 12-Lead ECG done several minutes into the call is very different from the original rhythm strip. The P waves are slightly irregular, with an average rate of about 47 bpm. (Marked with blue arrows on the labeled ECG). The QRS complexes are also slightly irregular, but not at all related to the P waves. It appears to be a right bundle branch block pattern, with a pathological Q wave in V1. Because of the ST changes, it isn’t possible to discern a small S wave in Leads I and V6, as we would normally see in RBBB. This appears to be a junctional rhythm that averages about 51 bpm. I would call this a complete heart block, even though complete heart block usually implies that the atrial rate will be faster than the escape rhythm. In this ECG, I see no signs of the P waves conducting, even when they have ample opportunity – that is, they have not fallen into a refractory period. In fact, a few minutes after the 12-lead ECG was done, there was a period recorded of about four seconds with P waves only.
The most notable feature of this ECG is that there is extreme ST segment elevation in all leads except aVR and aVL. The J points are so high, it appears that the QRS complexes are extremely wide. A second view of this ECG is provided with the J points marked with red lines to help you see where the QRS ends and the ST segment begins. These types of ST segment elevations are often called “shark fin” pattern. Rather than wide QRS, this pattern represents a blending of the QRS and T wave. Shark fin pattern is often seen in “related leads”, leads that are oriented to one coronary artery. In this case, the ST elevations are very widespread. Without knowing this patient’s outcome, I can only make an educated guess, that this is a Type 2 M.I. Type 2 M.I. is defined as an M.I. caused by a mismatch between cardiac supply and demand, rather than by thrombosis. Especially in coronary arteries that are narrowed by disease, a low-perfusion state can cause myocardial damage and elevated troponins. This patient has severe hypovolemia and anemia due to her G.I. bleed. Another possibility is an occlusion from a thrombus in a dominant artery. For example, one of the branches of the left coronary artery could wrap around and perfuse the inferior wall, which is usually the right coronary artery's territory. An occlusion in a markedly dominant artery can cause widespread ST changes. I would be very interested in hearing your thoughts on this.
For more information on shark fin pattern, and myocardial infarction in general, we highly recommend Dr. Steven Smith’s excellent blog. Dr. Smith is an authority on M.I. ECG changes, and the shark fin pattern. http://www.hqmeded-ecg.blogspot.com