Feb 5, 2021 This Week in Cardiology Podcast

John M. Mandrola, MD


February 05, 2021

Please note that the text below is not a full transcript and has not been copyedited. For more insight and commentary on these stories, subscribe to the This Week in Cardiology podcast.

In This Week’s Podcast

For the week ending February 5,2021, John Mandrola, MD comments on the following news and features stories.

COVID, Briefly

My review of the Johns Hopkins site today reveals continued good news. Cases are on a steep decline. Every day more and more people receive vaccines, and on social media, you no longer risk cancellation if you mention herd immunity. Still, I was in the ICU yesterday and I asked the nurses how the COVID situation was going: a nurse, who was donning her PPE, responded: “it’s like Groundhog Day.”

What I took from her words and her look was—get out of here with your optimism; I’ll believe it when it I see it. When historians tell the story of this pandemic, I hope the ICU and emergency department nurses and support staff get some serious recognition. It’s impossible to pass them in the hallway or cafeteria and not feel reverence towards people who work in these units EVERY SINGLE DAY.

Carotid Screening

This week, the US Preventive Services Task Force (USPSTF) reaffirmed its recommendation against screening for asymptomatic carotid stenosis (CAS).

The USPSTF is an independent volunteer group of national experts in prevention and evidence-based medicine. The 16 members come from behavioral health, family medicine, geriatrics, internal medicine, pediatrics, obstetrics and gynecology, and nursing. I went through their conflicts; I saw no relationships with industry.

The task force based their recommendation against looking at carotids on evidence that the harms outweigh the benefits.

  • First is the scope of the problem of CAS. One way to assess this is using something clumsily called population attributable risk (PAR), the number or proportion of cases (here, stroke cases) that would not occur if the risk factor would be eliminated. The PAR depends on the prevalence of the risk factor and the strength of its association with the disease.

    The prevalence of asymptomatic carotid disease in older adults is low—about 0.9%. Contrast that with hypertension, which is super prevalent. The PAR for stroke related to carotid artery stenosis is just 0.7%. The PAR for hypertension is 95%, for smoking, 12%-14%, and for high lipids about 9%. Thus, even if there was a perfect way to treat asymptomatic carotid disease, it would have very little effect on stroke rates in the population.

    The evidence that carotid endarterectomy (CEA) improves outcomes over medical therapy is dubious. The ACAS, ACST, and VACS trials comparing CEA to medical therapy were done nearly 2 decades ago. The risk reduction in stroke was about 2% in absolute terms, with a number needed to treat (NNT) of about 50.

    Dr Steven Spence’s group has a paper showing that the risk of stroke at the time of 100% carotid occlusion has been reduced over time (remember the brain, even more so than the heart has built in collateral vessels). As journalist Sue Hughes points out in her coverage, there are now two ongoing RCTs looking at interventional approaches vs meds in patients without symptoms.

  • The data for carotid intervention with stents does not look any better than CEA. In fact, a Cochrane review of 22 trials involving nearly 10,000 patients found that perioperative strokes are higher for stenting and this tilts the balance in favor of CEA.

  • Let’s consider what a positive test means. A systematic review estimates a 90% sensitivity and 94% specificity of color duplex ultrasound for CAS greater 70%. So, let’s take an incidence of 5% of CAS in the population. What are the chances of having the disease if you have a positive test? Applying the Bayes theorem, we find that, the average patient being screened for CAS is more likely to have a false-positive than a true positive.

  • Think about all that can happen with either a true positive or a false positive. If the patient has surgery there are the risks of surgery—stroke is the biggest. If the patient is sent to the doctor for further evaluation, there are the costs and risks of downstream testing.

  • You might argue that if we detect disease, we can get the patient on statins and lifestyle therapy. Here’s the problem with that logic: all patients can reduce their risk of vascular disease with lifestyle changes, and nearly all high-risk patients who have disease discovered, would have been high-enough risk via a simple PCE to recommend statins.

My friends, screening asymptomatic people for anything is an intervention. If you think it is beneficial, theoretical advantages are not enough. Given the potential costs and harms of this test, you have to prove the benefits of this intervention through randomization. Until then, the USPSTF is spot on.

Subcutaneous ICD Recalls

Recently, the US Food and Drug Administration (FDA) issued a Class I recall of the lead used in the subcutaneous implantable cardioverter defibrillator (S-ICD).

An implantable ICD is a simple device designed to decrease the risk of death by detecting and shocking ventricular arrythmias. The standard or transvenous kind involves putting a lead into the veins and then the heart. This lead inside the heart can pace and sense and defibrillate the heart. Numerous highly convincing RCTs have shown that these devices, when used in selected patients, save lives relative to medical therapy.

The Achilles heel of these devices is that the leads don’t last forever, they can fracture and that can cause oversensing and painful inappropriate shocks. They can also get infected leading to blood-borne infection and/or endocarditis. Moreover, if the leads have been in place for years, removal can be a high-risk procedure, because over time, leads scar in place.

The subcutaneous device avoids the risks of having leads in the blood vessels and the heart. With a S-ICD, the generator is in the left midaxillary area and the lead is outside the chest wall, close enough to the heart to sense and shock the patient out of ventricular tachycardia or fibrillation. But not having leads in the heart comes with the downsides of not being able to pace the heart and having to use higher energy to shock the heart. Some early studies have suggested that over time, the energy required to defibrillate the heart with an S-ICD may exceed the output of the device. Obviously, this is a problem.

Surely, since the outcome of interest here is death, proper trials have compared standard transvenous devices to S-ICDs and they are equivalent over long follow-up. Well, no, not really.

I’ve recently reported on the PRAETORIAN trial which seemed like a fair comparison, but it was clearly not. For one, the median follow-up was only 4 years. The concern about transvenous leads is not over 4 years but over 10 or more. For another, PRAETORIAN used a non-inferiority design and counted outcomes that everyone knew would go in opposite directions.

Now, back to the FDA recall. Such a lead failure could prevent the device from delivering shocks as needed, the agency said in its recall announcement, which applies to about 20,000 devices manufactured from March 2016 to November 2020 and distributed until November.

Alcohol and AF

In the early days of my training, we called it holiday heart, that is the association between high-dose alcohol intake and atrial fibrillation (AF). Now, numerous observational studies have shown an association between smaller doses of alcohol intake and AF. The relationship seems linear—the more alcohol one takes, the more the risk of AF.

And a recent study from Alex Voskobonik found that in patients with AF, abstinence from alcohol significantly reduced AF burden. But why is this?

Drs. Greg Marcus and Ed Gerstenfeld from UC San Francisco have published a small but elegant study that provides some potential clues as to the mechanisms. They randomly assigned 100 patients who were undergoing AF ablation to an IV alcohol infusion vs a placebo infusion. They then measured refractory periods and conduction velocities in the right atrium, left atrium, and pulmonary veins. Pulmonary vein atrial effective refractory periods (AERPs) decreased an average of 12 ms in the alcohol group, with no change in the placebo group (p = 0.98). Refractory periods and conduction times in the left atria did not differ. AF inducibility also did not differ.

These observations suggests that alcohol exerts direct and acute electrophysiologic effects on the atria, and particularly the pulmonary veins, which have long been known to be an important driver of AF. Having a shorter ERP is arrhythmogenic. This is because it increases the excitable gap in which reentry can occur. Having a shorter ERP in the pulmonary veins may be especially important for AF genesis.

I was surprised that the only significant finding was ERP in the pulmonary veins. Perhaps this was because the authors kept the alcohol dose at the legal limit. Perhaps a bit higher dose would have changed more of the parameters. A type 2 error is also possible in that more patients may have allowed them to see other changes.

Clinical Skills Exam Ended

There’s little good about the pandemic, but it’s here, and it will usher in some positive changes. One seems to be the abrupt cancellation of the Step 2 Clinical Skills exam given to fourth year US medical students.

Here’s what the testers devised to be the Step 2 Clinical Skills exam: They hired an actor to simulate a model disease, as if we ever see a model disease. Then make medical students travel on their own dime to one of only five sites in the United States. Charge them $1300 to take the test. It won’t matter if the student can’t hear the murmur, she or he only has to put the stethoscope in the four quadrants on the chest.

For nearly two decades, this utter folly was just another pay-to-play scheme for US medical students. Then the pandemic came, and in-person exams were unsuitable, so they abruptly and permanently cancelled the exam. The testers now say clinical reasoning and communication skills will be assessed in other steps.

Of course, they can be. Medical schools teach and assess these skills. So do internship and residency; but if people would only tell the truth, they would say it takes years of non-hobbiest clinical practice to master doctoring. And even then, medicine humbles you on regular basis.

The larger lesson here transcends fourth-year medical students to the silliness of many testing schemes. The American Board of Internal Medicine’s Maintenance of Certification program comes to mind.


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