Tag Archives: ecg

ECG lead placement: cheat sheet

22 Nov

always good to know where to hook up the leads

  • not only to be able to do it on your own
  • but also handy for checking placement if your ECG looks inexplicably odd (hint: go back and see where the stickers/leads are sitting on your patient’s chest)

 

for the LIMB LEADS:

if you’re lucky, they’re labeled and not faded, with RA (right arm), LL (left leg), etc.

in the UNITED STATES (colors are apparently different in Europe), here’s the mnemonic I learned:

think of it like 4 corners of your torso (where your limbs start):

  • smoke over fire (black over red)limb
  • white on right (hey, it rhymes)
  • by process of elimination the green lead goes in the one remaining corner of their torso (RL)

in EUROPE, the colors are apparently different, so if anyone has a mnemonic from across the pond, please feel free to share.

us-eu

 

PRECORDIAL LEADS (V1-V6):

here’s how I remember placement:

  • V1 is on the right sternal border, V2 is on the left sternal border: both are ~4th intercostal = nipple line
  • V4 is mid-clavicular, so I put it at the lower edge of pectoral/breast under the left nipple
  • V6 is mid-axillary, easy enough
  • then fill in the blanks: V3 (placed halfway between V2 and V4), then V5 (between V4 and V6)

there you go.

 

References: limb leads picture; european/us lead colors; precordial leads + picture

 

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pulmonary embolism ECG findings

30 Sep

Interesting article by Marchick et al from a 2010 Annals:

6,049 patients that a doc had enough suspicion for a PE to order testing (d-dimer, CTPA, V/Q scan).

Some tables worth eyeballing:

petable2

TAKEAWAYS:

sensitivity of all the ECG findings suck.  can’t rule out PE if you don’t see these.

specificity isn’t that great either (mostly in the 80s).  Among the better ones:

  • inverted anterior (V1-4) t-waves
  • S1Q3T3 (classically taught)
  • RBBB

petable3

 

TAKEAWAYS:

some context for you: compare the odds ratio of the d-dimer (a notoriously non-specific test that is elevated by many things), vs. the odds ratio of some of the more specific ECG findings.

so seeing these (e.g. anterior TWIs, S1Q3T3) may increase your suspicion for a PE, by no means is it a slam dunk.  Keep an eye out for these ECG findings, but take ’em with a grain of salt, keep your mind open.

 

References: annals article (tables from article).

Sgarbossa and pacemakers

18 Dec

quick refresher’s HERE and HERE

WHAT’S THE BIG IDEA WITH PACEMAKERS?

–ventricularly paced ECGs are tough to interpret for MI, because the signal starts somewhere other than the SA node/AV node/Purkinje fiber expressway, giving it a wide QRS complex pattern similar to a bundle-branch block

WHAT IF YOU USE SOMETHING THAT WORKS IN LBBB FOR PACED ECGs?

Study by Maloy et al:

57 study patients, retrospective review

  • ventricularly paced ECG
  • elevated cardiac markers <12hrs after ED ECG
  • diagnosis of AMI

99 control patients

  • ventricular-paced ECG
  • negative cardiac markers

A blinded board certified cardiologist reviewed all ECGs for Sgarbossa criteria.

RESULTS:

“ST-segment elevation of 1 mm concordant with the QRS complex”

  • no ECG fit this criterion;

“ST-segment depression of 1 mm in lead V1, V2, or V3,”

  • sensitivity was 19% (95% CI 11-31%),
  • specificity 81% (95% CI 72-87%),
  • likelihood ratio of 1.06 (0.63-1.64);

For “ST-segment elevation >5mm discordant with the QRS complex,”

  • sensitivity was 10% (95% CI 5-21%),
  • specificity 99% (95% CI 93-99%), 
  • likelihood ratio of 5.2 (1.3 – 21).

 

BOTTOM LINE:

 “the most clinically useful Sgarbossa criterion in identifying AMI was ST-segment elevation >5mm discordant with the QRS complex. This characteristic may prove helpful in identifying patients who may ultimately benefit from early aggressive AMI treatment strategies.”

translation: if you see discordant ST elevation >5mm in a paced rhythm, worry about an MI.

interesting that the least useful rule in LBBB might be the most useful in paced rhythms.

 

 

References: article, nice review on pacers at lifeinthefastlane; picture

Sgarbossa Criteria — modified

17 Dec

QUICK REVIEW:

–Sgarbossa criteria help look for STEMIs in people with LBBB (left bundle branch block)

 

ECG CRITERIA:
5 pts – concordant (same direction as QRS complex) ST elevation >=1mm any lead
3 pts – ST depression >=1mm in anterior leads (V1, V2, V3)
2 pts – discordant (opposite direction of QRS) ST elevation >=5mm any lead

–add up the points, score >=3 is 90+ percent specific for an MI

Smith et al study:

admission ECGs for all patients with an acutely occluded coronary artery and left bundle branch block

R or S wave, whichever was most prominent, and ST segments, relative to the PR segment, were msmith-sgareasured to the nearest 0.5 mm.

ST/S ratio was calculated for each lead that has discordant ST deviation of greater than or equal to 1 mm

cutoff for proposed rule was ST/S ratio <=  -0.25  (e.g. more discordant)

The study and control groups included 33 and 129 ECGs, respectively.

 

NOTABLE:

  • (3rd sgarbossa criteria) discordant ST-segment elevation of 5 mm was present in at least one lead in 30% of ECGs in patients AMI vs 9% of the control group
  • (proposed criteria) ST/S ratio less than (i.e. more negative than; more relative discordance than) -0.25 was present in 58% versus 8%.
  • Sensitivity of the revised rule (proposed ST/S ratio rule replaces 5mm ST elevation rule): 91% versus 52%.
  • Specificity of the revised rule was lower than that of the weighted rule (P=.002) and similar to that of the unweighted rule (P=1.0): 90%  versus 98% versus 90%.
  • Positive likelihood ratio for the revised rule 9.0
  • negative liklihood ratio for the revised rule 0.1

 

THEIR CONCLUSION:

“Replacement of the absolute ST-elevation measurement of greater than or equal to 5 mm in the third component of the Sgarbossa rule with an ST/S ratio less than -0.25 greatly improves diagnostic utility of the rule for STEMI.”

 

BOTTOM LINE:

the ST/S ratio rule seems more sensitive, similar specificity of old rule.

 

HOW DO I USE THIS?:
–you’re handed an EKG, there’s a LBBB

–look for >=1mm concordant ST elevation
–look for ST depression in anterior leads

–look for discordant ST deviation; if ST segment change is > 1/4th the amplitude of the R or S-wave, be curious

 

–if you see these things, worry about an MI

 

Reference(s): old post; article; picture is from the article

Can EKG abnormalities predict older adults with an increased risk of CHD events?

23 Jul

RAGING HYPOTHETICAL:

A 82 yo male presents with 3 hours of nausea. He has hyperlipidemia and hypertension, no hx CAD. He does not know his FMH. Vital signs are stable. His EKG shows a new RBBB. Pt never has any chest pain. What now?

Auer et al. “Association of Major and Minor ECG Abnormalities with CHD Events” JAMA April 11, 2012, Vol 37, No 14

Question: Can EKG abnormalities predict older adults with an increased risk of CHD events?

Methods: Population Based study of 2192 adults age 70-79. Baseline EKG was collected from 1997-1998. Repeat EKG done from 2006-2007. EKG were sent to central coders and classified as minor vs major abnormalities from baseline

Criteria for major prevalent ECG abnormalities:

  • Q-QS wave abnormalities
  • left ventricular hypertrophy
  • Wolff-Parkinson-White syndrome
  • complete bundle branch block or intraventricular block
  • atrial fibrillation or atrial flutter
  • major ST-T changes

Criteria for minor prevalent ECG abnormalities:

  • minor ST-T changes

Results: 351/2192 pts had a CHD event (death, MI, hospitalization). 782 pts had an abnormal EKG. Minor EKG changes had a hazarad ratio of 1.35 (95% CI 1.02-1.81) and Major EKG changes 1.51 (95% CI 1.2-1.9).

Teaching points: Risk stratification in elderly adults for CHD can be difficult as many can present without chest pain and do not have the traditional risk factors. A minimally abnormal EKG can help identify an elderly pt at risk for a serious cardiovascular disease.

Submitted by W. Rushton.

Reference(s): Auer et al. “Association of Major and Minor ECG Abnormalities with CHD Events” JAMA April 11, 2012, Vol 37, No 14; picture