Ask the Clinical Instructor

Todd is the Cardiology Manager for Memorial Hermann Southeast in Houston, Texas. He also teaches an online RCIS Review course for Spokane Community College, in Spokane, Washington, and regularly presents with RCIS Review Courses. While in a case with a physician, he mentioned that there was a “sign” on the monitor that confirmed the suspicion of the patient having hypertrophic cardiomyopathy (HOCM). I missed it. What could he have been talking about? – Via email, a Cath Lab Employee from New Hampshire Without seeing any hemodynamics data or screen shots, I can only guess that he may have been talking about the Brockenbrough response, which is typically indicative of hypertrophic cardiomyopathy (HOCM). The Brockenbrough response is seen in patients with HOCM. In the past, this used to be called idiopathic hypertrophic subvalvular stenosis (IHSS). Sometimes you might hear this as “subaortic” instead of “subvalvular.” Either way, the use of this term is antiquated. To understand, first, think about what pressures look like after a normal PVC. From last month’s article (The Frank-Starling Principle, available at https://tinyurl.com/FrankStarling), we know that in a healthy heart, when there is a PVC, there will be a pause between QRS complexes as the myocardium resets after the PVC. This delay invokes the Frank-Starling principle, in that the heart will pump out all the blood that is returned to it in diastole (to a point, of course). Since the post-PVC beat has had longer time to fill, the next systolic action of the heart will result in a higher pressure because of more blood being ejected (Figure 1). This is why patients can feel the “palpitation” from this beat. In HOCM, the post-PVC beat generates LESS pressure read on the AO transducer than the beats before and after. Following extra-systole, there is an increase in the gradient and development of a spike-and-dome shape to the AO waveform (also known as pulsus bisfieriens). Where we would expect an increased AO waveform, we now see a substantially decreased AO waveform. While this is rarely done, if you happen to be measuring AO and LV at the same time, you will see the increase of the LV pressure after the PVC, because the heart is trying to pump as it should, but the outflow gets blocked from the myopathic obstruction, which decreases the aortic pressure (Figure 2). Even if you are not recording the LV and the AO at the same time, anytime you have a lower pressure than expected beat after a PVC, as demonstrated in Figure 2, you should suspect HOCM, or other outflow track obstruction. While the discussion of HOCM can in itself take a full article, this quickly describes the Brockenbrough response, which is a classic sign of HOCM. Email your question to tginapp@ rcisreview.com.

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