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.
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.
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.
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.
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)
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,
- It is confined to a specific lead distribution– the lead with inconsistent connectivity.
- There is a chaotically wandering baseline.
- The cycle lengths are short (30-70Hz ?) and grossly irregular.
- 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.
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.
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A 35 yr old white male presents to EMS with 20 minutes of 8/10 burning epigastric discomfort and left arm numbness. He denies nausea and shortness of breath; he is non-diaphoretic. He appears fit, healthy, and eerily calm.The pt. relates that this is not his “typical heartburn.” The only thing it reminds him of is when, 10 years ago, “a truck I was working on fell on my chest.” His BP is 180/110; his glucose is 399mg/Dl. He states that he has no medical history and has not seen a doctor in years. His father had an MI at 45, and died of another at 56; his mother died of an MI when she was 53. Social history reveals 16 pack-years of smoking.
The following EKG was recorded on arrival at the ED:The initial prehospital 12-lead in this case demonstrates a junctional tachycardia with ST elevation in V2-5, I, and avL; reciprocal depressions are suggested in V6, III, and avF sealing the diagnosis acute anterolateral MI. Evidence of an inverted P-wave buried within the QRS complex may be appreciated in the first deflection of the depolarizations in lead I. Sinus tachycardia supervenes in the second and third prehospital 12-leads, as well as the tracing obtained on arrival in the ED. Note the dramatic Q waves and loss of R-wave progression seen across the precordium, often a valuable tool for differentiating STEMI from benign early repolarization. Also of interest in this case is the 7th complex seen in the third prehospital tracing. The QRS morphology here reflects that of the initial junctional rhythm, while the p-wave preceding the complex remains normative, perhaps indicating an event of junctional fusion.
Contiguous precordial ST elevations are typically associated with lesions of the LAD and circumflex. Although the majority of coronary systems are right-dominant with the AV nodal branch arising from the distal RCA, in a left-dominant system the AV node is perfused by a distal branch of the left circumflex. Thus, while the specific anatomy remains unknown here, the presence of junctional tachycardia may reflect an irritable AV nodal focus resulting from circumflex disease in the setting of left-dominance. The graphics below illustrate these coronary variants.
Anterior views of the coronary arterial system, with the principal variations. The right coronary arterial tree is shown in magenta, the left in full red. In both cases posterior distribution is shown in a paler shade. A, The most common arrangement. B, A common variation in the origin of the sinuatrial nodal artery. C, An example of left ‘dominance’ by the left coronary artery, showing also an uncommon origin of the sinuatrial artery. (Text and images retrieved from: http://pgmcqs.com/2011/05/17/anatomy-thorax/)
Coronary angiography in this case revealed an 85% proximal occlusion of the left circumflex, a 60% proximal occlusion of the first diagonal branch and a 40% diffuse occlusion of the second diagonal branch. Stents were deployed across the two more serious lesions, reducing their stenosis to 0% post procedure. A 22-minute DTB time was recorded. Documentation of cardiac enzymes was not available at the time of follow up, however this pt made a good recovery and was discharged several days post PCI.