Perhaps quite too often, the knee-jerk reaction to an elevated Troponin is to call our friends from Cardiology. This becomes a flawed philosophy when taking into consideration the coronary circulation and its potential alterations in the setting of acute illness. The heart consumes a tremendous amount of O2 at baseline, despite receiving only 5% of the resting cardiac output. To compensate, O2 in the coronary circulation is extracted in the myocardium by a much higher degree than it is in any other tissues. In fact, myocardial oxygen extraction is so high, that in conditions imposing greater workloads on the heart (Sepsis, Shock, Hypoxia), the only way to increase myocardial O2 is by increasing coronary blood flow altogether. To do this, the coronary vessels are typically able to dilate significantly…typically.
Consider Sepsis, a condition characterized by PERIPHERAL VASODILATION. How can the coronary vessels dilate further if they are already maximally dilated? In many situations they cannot, coronary ischemia ensues, and the Troponin rises. Cardiology cannot help us with this beyond advising us to treat the primary cause. Now consider Tachycardia, often a physiological response to acute illness. Recall, little coronary blood flow occurs during Systole with the majority occurring in Diastole. Even during the Isovolumetric phase of Systole, the LV generates enough compressive force to effectively block off the coronary circulation. There is a bit more Systolic flow on the right side as the RV generates much less force. The faster the heart rate, the less time there is for Diastole and thus, less time for coronary perfusion. In a healthy heart, this may not be an issue as the vessels can easily dilate and respond. But in our patients with CAD with already dilated vessels, or acutely ill patients with systemic vasodilation, this may not be the case. Once again, other than dealing with the primary disturbance Cardiology may not provide much more insight.
There is no “one size fits all” in medicine and there are situations which may be similar where Cardiology may truly be needed. Just keep in mind the coronary circulation, the presenting illness, and predisposing conditions of the patient before making the call.
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