Coronary Artery Dominance

Knowing which coronary artery has the blockage can help you understand the effects of an MI on the myocardium. And seeing regional wall motion abnormalities on echo can often tell you which coronary artery has the blockage. Because certain areas of the heart are supplied by certain coronary arteries. But, there is a trick. In most people, the inferior wall of the heart is supplied by the right coronary artery (RCA), but in some people, it is supplied by the circumflex (LCx). This is known as coronary artery dominance and this Instagram post from our friends over at foamfrat explains it in a little more detail.

Frank Starling’s Curve

OK, it’s not actually Frank Starling’s curve, it’s the Frank-Starling curve, named for Otto Frank and Ernst Starling. But for some reason, a lot of people refer to it as if it is named for some guy named Frank Starling. It’s a pedantic pet peeve of mine. But, I digress…

The Frank-Starling Curve, often referred to just as the Starling Curve is a super-duper important (of you’ll forgive the technical jargon) concept in cardiac physiology. Understanding it is key to resuscitation of critically ill patients. Fortunately, Rishi Kumar does a great job of explaining it.

Vasopressor Receptors

Different vasopressors have different functions and these functions dictate why we choose certain pressors at certain times. We’re all familiar (hopefully) with the fact that epinephrine is a positive inotrope as well as a vasopressor while phenylephrine is pure vasoconstrictor. This is why we choose epi over phenylephrine when we need inotropy and why phenylephrine will actually make hypotension secondary to cardiogenic shock worse.

These differences in function are dictated by the different receptors on which the pressor drugs act. In addition to different functions, some vasopressors with the same general effect (vasoconstriction) act on different targets (catecholamine vs non-catecholamine) and so can have a synergistic effect. Adding vasopressin to norepinephrine for a patient in septic shock, for example, can help even beyond the fact that norepi is at its limit. This is why adding vasopressin before maxing out norepi is often beneficial. Additionally, vasopressin is less affected by blood pH, so it will work in patients with extreme acidosis where norepi will not.

Eddy Joe Gutierrez has a great Instagram post on this with a nice slide showing how the different pressors work.

Harlequin Syndrome in ECMO

One of the big complications of VA ECMO is something called Harlequin Syndrome, also known as North-South Syndrome. It happens when the oxygenated blood being returned from the ECMO circuit mixes with the deoxygenated blood being ejected from the heart (there was a big reason the patient was put on ECMO, remember?). This is actually sometimes a good sign, because it means the heart is able to pump (you were on VA because of heart problems). But, the lungs haven’t really recovered yet, hence the deoxygenated blood being ejected. And so, despite the good news of better heart function, the patient still may end up in life-threatening hypoxia from this mixing.

As usual, countbackwardsfrom10 is our go-to for all things cardiac surgery, and he has a nice Instagram post explaining this phenomenon and what to do about it.

POCUS Diagnosis of Aortic Dissection

Acute Aortic Dissection is a medical emergency and often a difficult diagnosis to make. The classic presentation is tearing, mid-scapular pain, but because the aorta runs the length of the thorax and abdomen, dissection can present in various ways. I learned POCUS diagnosis of dissection as part of the RUSH exam, but that specifically looks at the abdominal aorta.

Arthur Broadstock, an EM PGY-3 at University of Cincinnati presents a great case over at Taming the SRU and looks at identifying Type A dissections with bedside POCUS. His case focuses on using the PLAX view of the heart to evaluate the aortic root. The suprasternal view of the aortic arch can also be quite useful and it’s probably the most under-taught view of the heart in terms of bedside echo.

For more on how to use that view, and lot more detail on the diagnosis of aortic dissection (Types A and B), see this nice post on POCUS 101.

Cardiac Axis

Determining the cardiac axis from a ECG is an important skill. And it’s one that confused me initially when I first started reading ECGs. It is a topic that still confuses a lot of my students. But David Schaack has created a handy interactive tool to learn this skill. He and Mike Cadogan recently wrote a quick piece over at Life in the Fast Lane. It’s a neat little interactive tool where you can drag the axis around and watch the ECG change. It’s something I’m going to be sharing with my students next semester for sure.

Are Subclavian Lines Better than IJ Lines?

A friend of mine recently told me a story. He was told by someone that new best practice guidance was coming that the subclavian site is going to be the preferred site over the IJ. The reason for this is the decreased rate of infections at the subclavian site as compared to the IJ. I wasn’t able to verify this recommendation, but I can verify that subclavian lines have reduced rates of infection and clots. In a large, multi-center study in France, subclavian lines had a little fewer than half as many infections or clots (1.5 per 1000 catheter-days) as lines placed in the IJ (3.6 per 1000 catheter-days). And, IJ lines actually aren’t a lot better than femoral (4.6 per 1000 catheter-days). Additionally, you avoid several big problems (particularly in trauma and neuro patients) by not reducing venous drainage from the head or getting in the way of c-collars.

So, why don’t we all go for the subclavian as our first site of choice? Because we’re afraid of pneumothorax. That same French study found triple the rate of pneumothorax in subclavian lines (1.5%) as compared to IJ lines (0.5%). This is the reason we always hear for avoiding the subclavian site. But, I suspect that that pneumothorax rate is mostly related to technique. Whereas most IJ lines are placed with dynamic US guidance, most subclavian lines are placed using the old landmark technique. However, I had an attending teach me the US guided technique when I was a brand new NP and I regularly use it to place subclavian lines. Now, I still place far more IJ lines than subclavians, but I suspect that’s mostly habit.

It’s not a hard technique and I’ve had lots of success placing these lines with (so far, knock on wood) no pneumothoraces. How do you do it? Well, Josh Farkas over at PulmCrit has a great article detailing the use of US and the “shrug technique” for placing subclavian lines.

So, if the rate of infection and clots is so much lower (not to mention the other benefits) and we can reduce the rate of pneumothorax to an acceptable level, should subclavian be the site of choice? I mentioned that I wasn’t able to verify this rumor that the Best Practice guidelines were going to change, but, at least in Europe, there may be movement towards just that. The French Society of Intensive Care Medicine (SRLF), jointly with the French-Speaking Group of Paediatric Emergency Rooms and Intensive Care Units (GFRUP) and the French-Speaking Association of Paediatric Surgical Intensivists (ADARPEF) recently issued an expert consensus statement on management of intravascular catheters in the ICU. They make 2 interesting recommendations in this area: subclavian is the preferred site for central venous access, and IJ is probably not any better than femoral.

The American Society of Anesthesiologists, in Practice Guidelines for Central Venous Access 2020, cites the same data from the 2015 French study, but stops short of recommending subclavian over IJ, saying only, “in adults, select an upper body insertion site when possible to minimize the risk of infection.”

Where do you place your central lines? Do you use ultrasound? What are your thoughts on your current practice in light of this information?

Measuring Blood Pressure in Aortic Dissection

Acute Aortic Dissection is a potentially life threatening vascular emergency. We’ve previously discussed the classification of dissection and briefly looked at conservative management in the form of impulse control. The idea is to reduce blood pressure and slow the heart rate to prevent worsening of the dissection either until it can heal or until surgical correction can be performed.

But, what’s the best way to monitor blood pressure in these patients? My practice is to place a radial arterial line in any patient with an acute aortic dissection. But, is a cuff adequate? Which arm should be used? Academic Life in Emergency Medicine (ALiEM) recently featured a post looking at the evidence to possibly answer these questions.

Classically, these patients will have different blood pressures in each arm, although this is not a universal finding. This difference may be predictive of dissection, but a 2018 study found that “any recorded difference in volume/force [of the pulse] or difference in obvious signs of malperfusion” was better at diagnosing acute aortic dissection. In the case of different systolic blood pressures in each arm, the higher of the 2 should be used to guide antihypertensive therapy. So, check both arms with a cuff and place the arterial line in the side with the higher pressure. You can continue to spot check the contralateral arm with a cuff as well.