There was a time before prehospital 12-leads when I learned why we need prehospital 12-leads.
The details are sketchy, but during paramedic school in 1995, I was treating a cardiac patient who presented with ST elevation in lead I. As for the other leads … well, there were only I, II and III on my Lifepak 10 – not much to go on. I knew ST elevation was a sign of badness – a heart attack, for example – but you had to view contiguous leads to justify that suspicion. Leads II and III were contiguous to each other, not to lead I.
I wanted to impress my paramedic preceptor, though, so I called the rhythm something like “sinus tach with ST elevation.” He just smiled at me, which I took to be validation of my brilliance, and helped load the patient on our rig. Once we were rolling, he said, “Let me show you something.”
He reached across the patient from the bench to the monitor and pressed RECORD to run an EKG for lead I. Then he did it again, only this time, he held the button down for a couple of seconds until DIAG appeared on the screen and the LP10 started to print. He tore apart the two strips and showed them to me.
The first tracing presented pretty much the same sinus rhythm and ST elevation I’d noticed before. The second strip was similar to the first, but with more artifact and something else much more important: the ST segments were depressed instead of elevated!
“What did you do?” I asked my wise and influential mentor.
“I ran that last one in diagnostic mode,” he said. “It means we’re getting more reliable ST segments.”
Later I learned the Lifepak’s diagnostic mode produced EKGs using a wider range of frequencies: 0.05-100 Hz instead of the 1-30-Hz default [1]. Although the augmented frequency could lead to more baseline drift and artifact, the expanded lower end also produced more accurate ST segments. That meant our patient’s true lead-I EKG was the one with ST depression instead of elevation – a change in direction that begged the question, what about leads II and III?
After finding true ST elevation in diagnostic tracings of both reciprocal leads, we suspected an inferior-wall or right-ventricular MI. When my preceptor explained that this sort of analysis can be expanded easily and routinely to many other views of the heart with modern 12-lead technology, I couldn’t wait to make use of those state-of-the-art monitors prehospitally. I signed up for a 12-lead course with Tim Phalen, an acknowledged EKG guru, and became an early and eager disciple.
I soon discovered that although learning about 12-leads wasn’t hard, doing them prehospitally could be.
Prehospital complexities
Six of the 12-lead’s electrodes – the precordial or V leads – required much more precise placement than three-lead electrodes. To locate landmarks, you had to expose the patient’s chest – often without sufficient privacy. I think most male paramedics felt awkward anyway about lifting a breast to attach those leads.
“Acquiring” the EKG was another new step: it meant keeping the patient and the ambulance still for a few seconds while the machine processed all those electrical impulses and turned them into 12 concurrent mini-tracings.
Then there was the matter of managing our new Lifepak 11 – a mid-’90s, first-generation prehospital 12-lead contrivance. The 11, like its grandchild, the Lifepak 5, consisted of two separable modules: a monitor and a defibrillator.
The monitor screen was bigger than the Lifepak 10’s, but not tall enough to stack multiple leads as clearly as future Physio/Medtronic models could. The defibrillator could be operated stand-alone unless the user needed to pace or cardiovert a patient. However, it was risky in a career-ending sort of way to leave either half in the truck.
The 12-lead payoff
Still, it was exciting to be doing 12-leads prehospitally. In 1995, the Long Island system I was working in got an early start on STEMI notifications with a pilot program involving not just paramedics, but EMTs who were taught to attach electrodes, acquire EKGs and send them to medical control, where they could be read and forwarded to the appropriate ED. Transmission problems in those early days of cellular networks limited effectiveness, but New York liked the program enough to reinstate it in 2016.
Today, a proliferation of STEMI centers makes prehospital 12-lead interpretation in populous areas a necessity rather than an option. Paramedics and, to a lesser extent, EMTs, call in STEMI alerts directly to receiving hospitals, saving time and heart muscle. According to the American Heart Association, prehospital 12-lead EKGs have reduced mortality 24-32 percent, depending on whether PCI (cardiac catheterization) or fibrinolysis is used for reperfusion [2].
For me, it all started with those first three leads and a little luck.
References
1. Lifepak 11 Operations Manual. Physio-Control. 1995.
2. O’Connor R, Al Ali A, Brady W, et al. Acute Coronary Syndromes: 2015 American Heart Association Guidelines Update for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2015;132:S484-S485.
