Conveyor Belt Medicine: Where Are the Brakes?

Jaya Mallidi, MD, MHS


June 03, 2019

"Wisely and slow; they stumble that run fast."
—William Shakespeare

I stumbled when Ms B was my patient. I met her for the first time as she lay on the cath lab table, draped in the overflowing sea-blue sheet with only her face visible to me. Her blonde hair was sticking to the beads of sweat on her temples. I felt a familiar heaviness at the center of my chest—an inner voice of caution that is amplified when I don't get time to evaluate or talk to the patient before the procedure.

Jaya Mallidi, MD, MHS

I introduced myself in a muffled voice through my mask. "Ms B, I'm Dr Mallidi. Do you have any chest pain now?" She drowsily replied, "No." I looked at the ECG. The machine-interpreted reading said, "Anterior ST-segment elevation myocardial infarction (STEMI)". I saw the tall T waves in the precordial leads without any reciprocal changes. I looked at Ms B again. A serene countenance. Not what I would expect from an ongoing STEMI. Ignoring the increasingly uncomfortable tightness in my chest, I calmly asked the nurse, "Do we have labs? What is the potassium?" After what seemed like an eternity: "We don't have any lab results. They couldn't be drawn in the emergency department."

Fifteen minutes earlier, I was wrapping up my Friday afternoon in clinic, when I was asked to help because the on-call interventional cardiologist was tied up in another procedure. The brief report from the emergency department: "Forty-five-year-old woman with hypertension and diabetes, presented with nausea, chest pain, and altered mental sensorium. Anterior STEMI on ECG. Stable, on her way to cath lab." Ms B was placed on the STEMI conveyor belt and rushed to the cath lab.

I needed a moment to think. High levels of potassium (hyperkalemia) can mimic anterior STEMI on ECG. I was staring at the ECG. All eyes were staring at me, wondering why I was not rushing. Time was of the essence if Ms B was truly having a heart attack from an occluded artery. I was not sure she was. To proceed with angiography or not?

No Stopping the Belt in Motion

Classic conveyor belt medicine is a fast-paced system that encourages reflexive actions, largely to meet quality metrics, and discourages meaningful patient interactions. The second the ECG was interpreted as "anterior STEMI," Ms B was placed on the conveyer belt. A single snippet of clinical information interpreted by a machine set the belt in motion. Her clinical history, symptoms, physical examination, and labs didn't matter. Her understanding, and accurate informed consent, mattered even less. The conveyor belt was now moving so fast that I could not stop it.

Ms B had a normal angiogram. She had stopped taking her insulin for diabetes, and had ketoacidosis with associated hyperkalemia that mimicked anterior STEMI on the ECG. Ms B had no complications from the angiogram. However, she underwent a procedure that she did not need, and was subjected to the risk for complications. From a population-wide perspective, there may be an acceptable false-positive activation rate so as not miss a true STEMI. From an individual patient perspective, I question it every single time.

The regional STEMI systems of care have undoubtedly reduced the time from first medical contact to reperfusion by primary percutaneous coronary intervention (PCI). Such measures as prehospital ECG transmission to centralized systems and direct cath lab activation by emergency physicians helped in streamlining the systems of care to reduce reperfusion time and improve outcomes in patients with STEMI.[1] The door-to-balloon time (D2B) became synonymous with quality and is publicly reported. Across the nation, more than 80% of patients with STEMI are treated within the guideline recommended D2B time of < 90 minutes,[2] such that the Centers for Medicare & Medicaid Services stopped providing a financial incentive for hospitals to achieve this metric.[3] It is no longer a discriminating quality metric between hospitals.[3]

By choosing the D2B time as a core quality metric, we oiled the conveyor belt to improve outcomes for patients with clinical history, ECG, and angiographic evidence of STEMI. But we forgot to put in checkpoints or brakes to stop the conveyor belt when needed. There are several clinical conditions—from benign pericarditis to life-threatening aortic dissection—that mimic STEMI on ECG. The sensitivity and specificity of standard computerized algorithms to diagnose STEMI on ECG have limitations.[4]

Automatons Versus Clinicians

Where are the brakes? The task of finding brakes where they don't exist falls to the interventional cardiologist.

The system has made it difficult to stop the conveyor belt before angiography. To even transiently pause the belt to assess the patient carefully, wait for labs, try to reach family for more information, or do additional testing in consideration of an alternative diagnosis takes a Herculean effort, prompting discussions that breed interdisciplinary distrust against the backdrop of the ticking clock. Bedside clinical evaluation and critical thinking to overcome the anchoring bias of STEMI diagnosis based on machine-interpreted ECG has been stripped away by conveyor belt medicine. The culture has so deeply penetrated our psyches that we work like automatons pursuing metrics that may not be relevant to the patient in front of us.

The burden of decision-making shouldered by interventional cardiologists in terms of when and where to stop the conveyor belt is hugely challenging. After more than a decade of regional STEMI networks, the literature on patient outcomes, overutilization of resources, and economic burden due to activation of the conveyor belt among patients without true STEMI are limited.[5,6] Given the multitude of clinical scenarios that can mimic STEMI on ECG and the heterogeneity in clinical presentation associated with each of them, variability in institutional cultures and physician practices in stopping the conveyor belt before the designated angiogram make it challenging to even name and define problem. Should we call it a "false STEMI alarm" or "inappropriate activation"?

Unlike D2B time, there is significant institutional variability in the rate of initiation and cessation of STEMI activations. Depending on the definition, anywhere between 10% and 65%patients placed on the STEMI conveyor belt do not have a clinical condition that warrants emergent coronary angiography.[7,8] This metric is not reported publicly. Discussion of the problem may remain confined to postcall hallway conversations, unless there is a strong physician champion voicing this concern to bring about an institutional cultural shift to allow for brakes on the conveyor belt when needed.

Interventional cardiology as a field is moving toward regional systems of care for patients with even more heterogenous clinical presentations, such as outside hospital cardiac arrests or cardiogenic shock. As we do this, we must improve the networks and algorithms used to build these systems by defining and choosing parameters that encourage comprehensive clinical evaluation and management in conjunction with relevant time-sensitive metrics. Let us begin to choose wisely and avoid stumbling in the haste of conveyor belt medicine.


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