Artifact from Frayed Leads Obscures STEMI

Introduction:

Artifactual activity on 12-lead EKG presents a significant impediment to electrocardiographic diagnosis. A case is presented here in which underlying STEMI could not be appreciated due to artifactual interference from frayed electrode leads. Clinicians should to be aware of the causes and presentations of EKG artifact in order to avoid similar pitfalls.

Methods:

An “all fields” PubMed search was conducted using the term “artifact” in conjunction with each of the terms “STEMI”, “myocardial infarction”, “EKG”, “ECG”, and “ST segment.”  Results yielded 0, 76, 19, 317, and 22 references respectively. These 434 citations were then screened for relevance according to title. The scope of the search spanned from 1973 to June 2012.

Review:

Numerous sources and types of artifactual interference on EKG have been identified. Artifact may be defined as any electrical activity present on EKG recording which does not directly and appropriately reflect cardiac activity. Artifactual interference may be classified as either of primary, non-cardiac etiology, or of secondary etiology when authentic cardiac signals are deranged due to incompetent acquisition, processing, or presentation. In the former category, a multitude of electrical and mechanical devices have been implicated (1-12, 46). Movement artifacts such as patient tremor, respiration, coughing, and hiccups have also been described (13-21, 43, 44). Artifact resulting from bed or stretcher movement should also be included in this subgroup.

Regarding the derangement of authentic cardiac signals rather than non-cardiac interference, investigators have noted an extensive variety of effects due to electrode misplacement (25-28, 32, 37). Acquisition filters have also been found to deceptively alter the appearance of the electrocardiogram (30, 33). Inconsistent electrode contacts as well as flawed or inverted lead connections can be problematic (45). Printers, monitors, and electronic transmission software have all been implicated in significant distortion or augmentation of the EKG (29, 41).

Too numerous to count case reports involving both primary non-cardiac interference as well as secondary artifact effects have illustrated a diversity of arrhythmic, ischemic, and other electrocardiographic mimics. Typically low frequency primary artifact resulting from tremors or rhythmic movement of physiologic cycle length has been associated with the mimicry of dysrhymias, often wide complex dysrhthmias (13-21, 23). Derangements of authentic cardiac activity resulting from lead reversals, filtering effects, and post-acquisition processing have frequently been associated with the mimicry of ischemic EKG patterns. The appearance of pathologic Q-waves, dramatic changes in cardiac axis, T-wave deflection, and alterations of R-wave amplitude and progression have been documented (25-27). False ST elevation and depression have also been described (30, 31). Both the masking of intrinsic pathology and the pathologic representation of healthy cardiac signals have been noted (30-34, 40, 45). The consequences of unrecognized artifactual interference can include inappropriate pharmacological and electrical therapies; significant morbidity and mortality has resulted (15, 18, 19, 28).

In some cases, the clinician can exploit artifactual activity. Shivering artifact in the presence of electrocardiographic evidence of hypothermia is such a case (42). The utility of respiratory artifact has also been explored (24). More recently, the exploitation of systematic computer algorithm interpretation error has been discussed relative to “double counting” of heart rate in the setting of hyperkalemia (41).

In this case report, an anterior ST-elevation myocardial infarction was masked by opaque artifactual activity resulting from frayed electrode leads. To date, this would appear to be the first documented case of such an occurrence.

Case Presentation:

An 85 year-old Caucasian man with a history of atrial fibrillation and anxiety awoke at 2:30 AM with chest pressure and shortness of breath. He alerted his daughter and she administered his Xanex, believing his symptoms to be psychosomatic. When this had little effect, an ambulance was called. On their arrival at 3:40 AM, paramedics administered oxygen and 162mg of aspirin. Vital signs at this time were within normal limits. A rhythm strip was acquired which demonstrated heavy artifact obscuring all but one lead. Additional leads were not visualized and no intelligible 12-lead could be obtained.

The patient was transported to a non-PCI capable community hospital. There, a 12-lead EKG was recorded which showed explicit anterior wall STEMI.

The troponin was 0.65. Tenectaplase was administered at 4:30AM; a repeat EKG 90 minutes later was unchanged. At this time, he was transferred to an outside hospital for cardiac catheterization.

On arrival at 7:05AM, the patient was hypotensive with a systolic blood pressure of 70mmHg.

An aortic balloon pump was placed and dopamine initiated. A complete occlusion of the mid-LAD was identified; thrombectomy was performed and the vessel stented with TIMI3 result. Hypotension persisted and the patient developed increasing lethargy and dyspnea. He vomited and became apenic while in cath lab. At 8:15AM he was intubated and placed on levophed; his ejection fraction was less than <15%. Hypotension remained refractory despite the addition of vasopressin and dobutamine. At 10:25AM, the troponin was 92. At this time he was unresponsive on exam with central cyanosis and mottling to all four extremities. There was pulmonary edema with an arterial line indicating a systolic BP of 50mmHg. Blood gas analysis indicated a pH of 7.10. He was described as not likely to survive and made DNR at 10:50AM. At 11:58 AM no carotid pulse could be appreciated and he was pronounced dead.

Discussion:

Retrospective analysis of the prehospital EKG artifact was undertaken. The system was traced from the electrode-lead junctions back to the monitor. In this case, a Physio-Control Life Pack 12 device was being utilized and revealed cable-junction fraying. Experienced operators of this device are often familiar with this type of artifact, and the cable-junction is a known weak point.

Cable fraying or, more broadly, lead-connection artifact, has a distinct electrocardiographic signature. Fequentlely there is an erraticly wandering baseline with sharp, irregular voltage spikes showing inconsistantly varrying amplitudes. As usualy only one connection is effected, the artifact should localize to a particular lead. Thus there should also be leads present which are free of artifact.

Note that in the initial EKG from this case there are voltage spikes of varying amplitudes, a chaotically wandering baseline, and a lead-specific artifact distribution. Other etiologies may mimic lead-connection artifact, but are readily distinguishable once they become familiar to the clinician.

60Hz AC interference should demonstrate almost exactly 60 deflections per second; the baseline typically will not wander and the amplitude will be constant or demonstrate orderly undulation. (Image retrieved from “Doktorekg.com,” http://www.metealpaslan.com/ecg/artef3en.htm)

Artifact from nerve or muscle stimulators should also be of fixed amplitude and hold to a stable baseline. (1)

Shivering artifact may or may not be accompanied by hypothermic ECG stigmata such as bradycardia or Osborne waves; note that the artifact is not confined to any single lead distribution. (Image retrieved from “LifeInTheFastLane.com,” http://lifeinthefastlane.com/ecg-library/basics/hypothermia/)

Artifact from resting tremor is typically of lower (physiologic) frequency and thus can mimic VT or a-flutter; relative to lead-connection artifact, tremor interference is pervasive, consistent, and of much longer cycle length.

The distinguishing hallmarks of lead-connection artifact are,

  1. It is confined to a specific lead distribution– the lead with inconsistent connectivity.
  2. There is a chaotically wandering baseline.
  3. The cycle lengths are short (30-70Hz ?) and grossly irregular.
  4. The amplitude is widely variable and randomly distributed.

When lead-connection artifact is recognized, operators can trouble-shoot the system  for correctable problems. Often a “positional” solution can be temporarily utilized to acquire an acceptable tracing before the cables can be replaced. As in this case, when the origin of the artifact is unknown to the practitioner, it is not possible to investigate such a solution. The tragic coincidence presented here, where in the detection of STEMI was obscured by lead-connection artifact, illustrates that the potential significance of this issue.

While newer lead hardware has been made available, many operators continue to utilize the monitoring cables described in this case.

Conclusion:

In this case, an anterior wall STEMI could not be appreciated due to artifactual interference. The patient was therefore transported to a non-PCI capable facility; subsequently, he did not receive definitive reperfusion until nearly five hours after his initial encounter with ACLS providers. The result was a catastrophic infarction from which he could not recover.

Operators should be familiar with the appearance of lead-connection artifact and maintain a high index of suspicion when checking and trouble-shooting this hardware.

References

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9 responses

  1. Excellent case study! Cable failures are sometimes subtle, and we featured such a case at EMS 12-Lead in which a pair of cables had a small break: http://ems12lead.com/2012/05/comparing-12-leads-discussion/

    July 30, 2012 at 4:57 pm

    • I was much impressed when I read your case report in re poor R-wave progression– an excellent catch from a QA perspective. Very interesting to hear that it was lead-fracture there as well. I suspect the incidence of this is not insignificant; as the comments from EMS12Lead indicate, many operators are intimately familiar with these equipment issues and their various presentations.

      As one of your readers points out: “They [cables] degrade rapidly and they fail commonly and more troubling, inconsistantly. They’ll be fine for the morning check, and then on your 3rd chest pain of the day, good-bye 12 lead capability…” This has been my experience as well; work with dramatically frayed leads for a week with no problems, but suddenly total artifact at the least opportune time.

      As always thank you for your insights, Christopher.

      July 30, 2012 at 5:23 pm

      • Christopher

        I think the honest answer is the wire gauge used for cost and convenience in EMS equipment is not necessarily up to the wear and tear placed on them! Wrapping, unwrapping, tangling, getting caught in corners, all of these cause repetitive stress on the wires themselves. Eventually they’re going to give out. Physio uses 4-cables versus Philips and Zoll with 3-cables; statistically Physio has more opportunities for failure :)

        Monitor manufacturers could probably apply a measure of impedance from the cables, given they know when they are and are not attached, and proactively note when cables may have degraded.

        July 30, 2012 at 5:38 pm

      • I’m with you– one imagines that a resistance test could be applied on monitor start up “self-test”, perhaps link the leads to one another to complete the circuit or something, and higher resistance or even some test for ambient instability would suggest fracture or attenuation of some of the filaments.

        The pragmatist in me, however, says that it is hard to convince people to take action to exchange leads let alone buy new ones until there is consistent unignorable evidence of failure.

        July 30, 2012 at 6:12 pm

  2. I don’t understand how a fractured lead is responsible. If lead III has no artifact then the white and red electrodes are not to blame. So then why should aVF show artifact? Seems strange to me.

    August 8, 2012 at 3:17 pm

    • Tom- Thank you for your attention and insight. The reality of the situation is that I am not totally sure what happened here. My understanding is that avF= LL-1/2(LA+RA)… this would suggest to me that if either LA or RA is compromised, avF will show the result; so if, for example, the RA electrode is damaged, leads II and avF will show artifact, but lead III may be clean. Is this correct?

      The truth, however, is that this case study is not really a case of artifact obscuring electrocardiographic diagnosis. If I had proof that both I and avL were also unintelligible then maybe the case could be made. But the code summary indicates that those leads were never visualized. So my guess is that this is a story more about what happens when you get used to monitoring in II, III, and avF, than it is about equipment failure.

      Thank you again for you comments!

      August 9, 2012 at 1:36 am

    • Correction: Should read “lead III has no artifact so the black and red electrodes are not to blame…”

      August 14, 2012 at 1:43 pm

  3. Steve

    Regardless of the manufacturer, pt. cables, accessories, and such have a limited life span. I know Physio recommends replacing all pt. and therapy cables after a certain period of use. I cannot believe that the pt. cables shown in the case study were even being used! Shame on the EMS service that allowed that, either by omission or commission. Can you see any healthcare provider working with something like that in that condition?

    August 8, 2012 at 5:33 pm

    • Steven- Thank you very much for your comments. I certainly sympathize with your position! Nonetheless, I must tell you that there are some places where the resources simply do not exist to proactively prevent problems before they occur. I have worked for agencies where half of the most important medications are expired (some not present at all), where the ET tubes are rarely sterile, capnography works only intermittently, etc.. I do not blame the agencies– they were doing the best they could under incredible economic and political pressures, and doing admirably with what they had. I was grateful to have end tidal waveform at all. Some of us worked 45 minutes from the base station with no backup– we made due or did without.

      I do not even consider these conditions I am describing to be “bad”. I was always astonished by the sincerity of the people for whom I was working and their commitment to the populations we served. I hear about places where you wash the BVM mask after the code. Where the trauma center is 4 hours away and it will take two hours to back-fill your position. Where there is no ALS.

      I very much share your values about the way things should be. But I do not feel ashamed. We (most of us) were doing the best we could.

      August 9, 2012 at 2:20 am

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