A woman in her 70s presented with chest pain. Her ECG showed atrial fibrillation and intermittent native complexes among predominantly paced complexes. Application of the Sgarbossa criteria to the ECG did not meet STEMI criteria. Serial ECGs showed ST changes in native complexes indicative of ischemia. Coronary angiography revealed a thrombus causing 95% occlusion, which was treated with stenting. This case highlights the challenges of diagnosing ischemia in paced rhythms and emphasizes the importance of evaluating native complexes, as the Sgarbossa criteria have limitations in paced rhythms.

1. Enhancing the Sgarbossa Criteria for the Diagnosis
of ST Elevation Myocardial Infarction
Timothy F. Simpson, MD, PharmD; Salman Rahman, MD; Nora Goldschlager, MD
Awomaninher70spresentedtotheemergencydepartmentwith
chest pain of 30 minutes’ duration. Her medical history included
coronaryarterydisease,ischemiccardiomyopathy,andtachycardia-
bradycardiasyndromewithatrialfibrillation.Shehadpreviouslyun-
dergoneimplantationofadual-chamberpacemaker,subsequently
upgraded to a biventricular pacing system for cardiac resynchroni-
zation therapy in the setting of worsening left ventricular ejection
fraction (<35%) and high pacemaker dependence.
On arrival at the emergency department, blood pressure was
114/44 mm Hg; pulse irregular, averaging 65 bpm; respirations, 20
per minute; and oxygen saturation, 93% on ambient air. Cardiopul-
monaryexaminationrevealedanS3gallopheardbestattheleftlower
sternalborder,tracedependentpittingedematotheankles,andno
other abnormalities. Laboratory data was remarkable for B-type a
natriuretic peptide level of 311 pg/mL (normal, <79 pg/mL) and ini-
tialtroponinIlevelof0.05μg/L.A12-leadelectrocardiogram(ECG)
was obtained (Figure 1).
Questions: What does the ECG in Figure 1 demonstrate, and
what is the appropriate next step in management?
Interpretation
The Figure 1 ECG shows the atrial rhythm to be fibrillation. The pre-
dominant QRS complex duration is 116 milliseconds, and occurs at
regular intervals at a rate of 60 bpm (QRS complexes 2-4, 7, and 10
intheleadIIrhythmstrip).Pacingstimuliareseenimmediatelypre-
cedingadominantRwaveinleadV1;thereisanorthwestmeanfron-
tal plane QRS axis consistent with, but not specific for, biventricu-
larpacing.1
Intermittentnativecomplexesareseen(QRScomplexes
1, 5-6, 8-9 in the lead II rhythm strip), with a normal duration (80
milliseconds) and frontal plane axis.
The ninth QRS complex demonstrates native interventricular
conductionwith1-mmSTsegmentelevationinV5,and2-mmSTseg-
mentelevationinV6.PacedQRScomplexesshow1-to2-mmSTseg-
ment elevation in the inferior and apical leads (II, aVF, and V5-V6).
Applying the Sgarbossa criteria2
for the diagnosis of ST eleva-
tionmyocardialinfarction(STEMI)inleftbundlebranchblock(LBBB),
which is extrapolated to paced rhythms, the ECG was interpreted
as not meeting the criteria for STEMI. The diagnosis of STEMI in the
presenceofLBBBismadeunderthecriteriaifthesummedscoreof
thefollowingcriteriais3orhigher:concordantSTelevationgreater
than 1 mm in leads with a positive QRS complex (5 points); concor-
dant ST depression greater than 1 mm in leads V1 through V3
(3points);and/ordiscordantSTelevationgreaterthan5mminalead
with a negative QRS complex (2 points).
Because of ongoing chest pain, serial ECGs were performed,
which revealed anterior (V1-V3) ST segment depression in native
complexes (Figure 2A). Posterior leads (Figure 2B, leads V7-V9)
showed native complexes with 1-mm ST segment elevation.
Clinical Course
The patient was given aspirin, atorvastatin, and nitroglycerin. After
posteriorleadsdemonstratedSTsegmentelevation,thepatientwas
takenonanemergencybasistothecatheterlaboratory,wherecoro-
naryangiographyrevealedacutethrombusintheleftcircumflexar-
tery causing 95% occlusion. Aspiration thrombectomy was per-
formed,andadrug-elutingstentsuccessfullyplacedacrossthelesion.
Figure 1. Twelve-Lead Electrocardiogram Recorded on Arrival at the Emergency Department
aVR V1 V4
V2 V5
V3 V6
aVL
aVF
I
II
II
III
VI
V5
Clinical Review & Education
Challenges in Clinical Electrocardiography
jamainternalmedicine.com (Reprinted) JAMA Internal Medicine Published online February 11, 2019 E1
© 2019 American Medical Association. All rights reserved.
Downloaded From: https://jamanetwork.com/ by Ramachandra Barik on 03/10/2019

2. Repeat troponin measurement 4 hours after presentation showed
alevelincreasedto6.12μg/L.Type1acutemyocardialinfarctionwas
diagnosed on this basis in the setting of ischemic ECG changes and
identificationofcoronarythrombusatangiography.3
Thepatientwas
discharged with instructions to take aspirin and prescriptions for
clopidogrel, atorvastatin, metoprolol, and captopril.
Discussion
This case highlights the challenge facing physicians in diagnosing
cardiacischemiainthesettingofventricularlypacedrhythms.Italsoem-
phasizestheimportanceofcloseinspectionofallECGleadsintheevalu-
ation of ischemia and intentional inspection of normal His-Purkinje–
conductedQRScomplexes,ifnoted,inanotherwisepacedrhythm.
In this case, application of the commonly used Sgarbossa
criteria2
tothepresentingECGdidnotfulfillthecriteriaforaSTEMI.
Notably,thesecriteriawerederivedinasmallcohortofpatientswith
conduction-system disease characterized by LBBB but no pace-
maker, where they proved to have high specificity (96%) but poor
sensitivity2
(36%)andthusalimitednegativepredictivevalue;meta-
analysis of several validation studies show similar results.4
Since the original publication, the Sgarbossa criteria have been
extrapolated to right ventricular paced rhythms where retrospec-
tiveanalysisshowedsimilartestcharacteristics.5
Thefurtherextrapo-
lation to biventricular paced ECGs, which have greater variability in
QRS complexes owing to heterogeneity in lead placement, is yet to
be validated, although studies are underway (NCT02765477).
ToincreasethesensitivityoftheSgarbossacriteria,Smithetal6
tested variations of the criteria in patients with LBBB, and con-
cluded that replacing the original third criterion (discordant ST el-
evation>5mm)withanewcriterion(“proportionallyexcessive”dis-
cordantSTelevation,definedasSTsegmentelevationamplitudeto
Swaveamplituderatio>0.25,withapositivetestresultmeetingany
1 of the 3 criteria) increased sensitivity to 91% with minimal effect
on specificity (98% to 90%).6
Application of this modified Sgar-
Figure 2. Twelve-Lead Electrocardiograms Recorded 30 Minutes After Arrival at the Emergency Department
aVR V1 V4
V2 V5
V3 V6
aVL
aVF
I
II
II
III
VI
V5
Standard leadsA
aVR V1 V7
V2 V8
V3 V9
aVL
aVF
I
II
II
III
VI
V5
Posterior leads V7-V9B
Clinical Review & Education Challenges in Clinical Electrocardiography
E2 JAMA Internal Medicine Published online February 11, 2019 (Reprinted) jamainternalmedicine.com
© 2019 American Medical Association. All rights reserved.
Downloaded From: https://jamanetwork.com/ by Ramachandra Barik on 03/10/2019

3. bossacriteriontothepresentingECG(Figure1)yieldsapositivetest
forSTEMI(10thQRScomplexleadV6STelevation,2.5mm;Swave
elevation, 6 mm; ratio, 0.41).
ThepresenceofnativeHis-Purkinjeconductioninthepresent-
ing ECG (Figure 1) allows direct evaluation of the native ST seg-
ment, which is altered in cardiac ischemia. Ischemic injury creates
voltage gradients, inducing abnormal current flow between nor-
mal and ischemic zones (so-called current of injury), which mani-
fests as deviations of the ST segment. A number of ECG abnormali-
ties may occur after return from ventricularly paced to normal
His-Purkinjeconductedcomplexes.Mostnotablearetransientper-
sistence of T-wave inversions (so-called cardiac memory or T-wave
memory) that can mimic ischemic changes.7
However, ST seg-
mentsremainunaffected,allowingforunimpededinterpretationand
application of current consensus STEMI criteria (new ST elevation
attheJpointof2mminmenor1.5mminwomeninleadsV2and/or
V3 and/or of 1 mm in other contiguous chest leads or limb leads).8
ThepresenceofnativeconductionwithST-segmentelevationshould
supersede application of the Sgarbossa criteria, even when the cri-
teria are not met, and prompt rapid revascularization.
Take-Home Points
• A focused inspection of all ECG leads should be undertaken in the
evaluation of cardiac ischemia. Special attention should be given
to native QRS complexes if they occur in an otherwise ventricu-
larly paced patient.
• In validated populations Sgarbossa criteria2
are relatively specific
and thus useful for diagnosing acute STEMI in the setting of con-
duction disease, but have low sensitivity and thus poor negative
predictive value. The criteria as modified by Smith et al6
moder-
ately improve the sensitivity.
• The application of Sgarbossa criteria has not yet been assessed or
validated in biventricular paced rhythms.
• T-wave inversions may occur after a period of abnormal ventricu-
lar depolarization.
ARTICLE INFORMATION
Author Affiliations: Department of Medicine,
University of California, San Francisco (Simpson,
Rahman, Goldschlager); Division of Cardiology,
Department of Medicine, Zuckerberg San Francisco
General Hospital and Trauma Center, San Francisco,
California (Goldschlager).
Corresponding Author: Tim Simpson, MD,
PharmD, University of California, San Francisco,
505 Parnassus Ave, San Francisco, CA 94131
(timothy.simpson@ucsf.edu).
Published Online: February 11, 2019.
doi:10.1001/jamainternmed.2018.7993
Conflict of Interest Disclosures: None reported.
REFERENCES
1. Fazelifar A, Jorfi F, Haghjoo M. Electrocardio-
graphic patterns in biventricular pacing delivered by
second-generation cardiac resynchronization
devices. Indian Pacing Electrophysiol J. 2018;18(1):
13-19. doi:10.1016/j.ipej.2017.10.007
2. Sgarbossa EB, Pinski SL, Barbagelata A, et al.
Electrocardiographic diagnosis of evolving acute
myocardial infarction in the presence of left
bundle-branch block: GUSTO-1 (Global Utilization of
Streptokinase and Tissue Plasminogen Activator for
Occluded Coronary Arteries) investigators. N Engl J
Med. 1996;334(8):481-487. doi:10.1056/
NEJM199602223340801
3. Thygesen K, Alpert JS, Jaffe AS, et al; Executive
Group on behalf of the Joint European Society of
Cardiology (ESC)/American College of Cardiology
(ACC)/American Heart Association (AHA)/World
Heart Federation (WHF) Task Force for the
Universal Definition of Myocardial Infarction.
Fourth universal definition of myocardial infarction.
J Am Coll Cardiol. 2018;72(18):2231-2264. doi:10.
1016/j.jacc.2018.08.1038
4. Tabas JA, Rodriguez RM, Seligman HK,
Goldschlager NF. Electrocardiographic criteria for
detecting acute myocardial infarction in patients
with left bundle branch block: a meta-analysis. Ann
Emerg Med. 2008;52(4):329-336.e1. doi:10.1016/j.
annemergmed.2007.12.006
5. Sgarbossa EB, Pinski SL, Gates KB, Wagner GS.
Early electrocardiographic diagnosis of acute
myocardial infarction in the presence of ventricular
paced rhythm: GUSTO-I investigators. Am J Cardiol.
1996;77(5):423-424. doi:10.1016/S0002-9149(97)
89377-0
6. Smith SW, Dodd KW, Henry TD, Dvorak DM,
Pearce LA. Diagnosis of ST-elevation myocardial
infarction in the presence of left bundle branch
block with the ST-elevation to S-wave ratio in a
modified Sgarbossa rule. Ann Emerg Med. 2012;60
(6):766-776. doi:10.1016/j.annemergmed.2012.07.119
7. Shvilkin A, Huang HD, Josephson ME. Cardiac
memory: diagnostic tool in the making. Circ
Arrhythm Electrophysiol. 2015;8(2):475-482.
doi:10.1161/CIRCEP.115.002778
8. O’Gara PT, Kushner FG, Ascheim DD, et al;
American College of Cardiology Foundation/
American Heart Association Task Force on Practice
Guidelines. 2013 ACCF/AHA guideline for the
management of ST-elevation myocardial infarction:
a report of the American College of Cardiology
Foundation/American Heart Association Task Force
on Practice Guidelines. Circulation. 2013;127(4):
e362-e425. doi:10.1161/CIR.0b013e3182742cf6
Challenges in Clinical Electrocardiography Clinical Review & Education
jamainternalmedicine.com (Reprinted) JAMA Internal Medicine Published online February 11, 2019 E3
© 2019 American Medical Association. All rights reserved.
Downloaded From: https://jamanetwork.com/ by Ramachandra Barik on 03/10/2019