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Myocardial Ischemia (MA66)
-True myocardial ischemia in kids is rare
-Must c/s it in w CP or other Dx than can cause ischemia (Kawasaki, etc)
-Most pts don't present until after a myocardial event
-This ch focuses on pts presenting w CP before/during an event
Definition:
-Myocardial Ischemia = VO2>DO2 to myocardium
-decr DO2 bc decr cor Q bc of cor spasm or obstruction --> acute cor synd or myocard infarction
-or w Nl cor Q, but severe hypoxia
-cyanotic heart dz, sev anemia, Hgb'opathies all have potential to --> signif hypoxia...
-incr VO2 w exercise, etc, can cause ischemia if there is limited supply
Hx:
-Chest Pain
-more likely to be ischemic if:
-exertional>rest, +dyspnea, +diaphoresis, +syncoope
-substernal pressure/burning (as oppose to pain), Pressure radiate to neck/arm,
generally reproducible w similar activity; short lived- 2-10min (not lasting for hours)
-If pt is able to continue to run/play and pain goes away despite ongoing activity, less likely ischemic
-PMH- unless +athero CAD (w htn, DM, tobacco, hyperlipid being relevant), PMH unhelpful otherwise, except for Kawasaki dz
-if +KD Hx, then must review PMH for KD Tx, echo results, f/u results etc
-also screen for fevers that might have been unrecognized KD
-FHx- check for Marfan's, aortopathies, and for HCM
-c/s past surgeries where cor arts were handled
DDx:
-non athero CAD and myocard ischemia causes are rare:
-Coronary Artery XX
-Anomalous CA's
-L main CA fr PA (LCAPA)
-L main CA fr R cor cusp
-RCA fr L cor cusp
-Cor Art Fistula
-Cor Art Spasm
-Thromboembolic/embolic CAD
-KD
-Cor Art dissection
-Ostial Cor Art dz after reimplantation (dTGA art switch, Ao root replacement, Ross)
-Intramyocardial bridging
-Myocardial XX
-HCM, DCM, Severe AS, tachycardia w limited cor Q
-Misc
-sev hypoxia/cyanosis
PE:
-Nl exam, or:
-Dynamic SEM fr HOCM
-nonobstructive HCM pt might not have LVOT murmur w dynamic maneuvers, but still have same risk for ischemia; still check for murmur w change fr squat to stand to check for HOCM
-cont murmur louder in diastole at LSB = cor fistula or anom L main CA fr PA (LCAPA)
-DCM and HF w JVD, +S3 or S4, holosyst MR murmur, periph edema, hepatomegaly
-Suprasternal notch thrill, syst ej click, harsh SEM = hemodynamically signif AS
ECG:
#1 test for ischemia
-d/o age, autonomic tone, HR, race, gender, body habitus
-standing, hyperventilating, Valsalva all affect ST segments w small degree of ST depr or T wave inversions fr position etc
-Best to check ECG during a CP episode or soon afterwards
-it is key to have a previous ECG or ECG while ASx to compare the two to see if the dynamic ST changes were there before the possible ischemic episode
-ECG d/o:
-ischemia duration
-BBB or WPW presence, or paced rhythm -all can change findings in ischemia
-myocardial ischemia extent- subendocardial or transmural
-ischemia location- ant/post
-duration, location, extent of ischemia --> changes on ECG
-if it was subendocardial or transmural effects the ST changes
-Acute transmural ischemia --> Tall T waves w ST elevation bc of epicardial injury at ischemic zone
ISCHEMIA LOCATION PATTERNS:
-Inferior --> II, III, aVF
-Ant-Lat --> I, aVL, V2-6
-Post --> V1-2, with tall R and ST depression, usually also with inferior changes
-subendocardial ischemia--> ischemic zone is twd the inner ventric layer, so the overlying precordial leads show ST depression (bc net force away fr the lead, see diagram)
-often seen in pts w chronic CP 2y to ischemia
-AbNl baseline ECG w BBB or preexcitation--> limit Nl findings, harder to Dx w ECG - look for Q waves...
-Peds/Teens- Nl varient and other dz can mimic ischemia ST changes.
-Repolarization changes, pericardial dz, digitalis effect, elec abNl all affect ST changes
-Completely negative ECG at time of CP is very predictive of nonischemic CP. with acute myocardial event of <2% among pts w/o prior CAD hx who have negative ECG in setting of +CP
Myocardial Injury Biomarkers:
-2hrs post injury, enzymes released can be detected in blood.
-Cardiac Troponin T & I and CK-MB all important biomarkers for myocardial injury.
-good Sp/Sn for myocardial injury
-start to rise at 2hrs, and continue thereafter
-at 12hrs, the CK-MB peaks
-by 24hrs, the Troponins' Sn is still high but CKMB Sn is low
-CKMB false + possible bc of trace amts in skeletal muscle, so if much skeletal damage, c/s false +
-cardiac ez are also high w perimyocarditis fr inflmn
-Troponin I and T more Sp than CK-MB for myocardial injury, but bc Troponins check for small amts of myocardial damage, it might not always be + bc of coronary art dz
-could be + w myocarditis, pericardial dz, trauma, so c/s the context
-Sn/Sp incr if check serial biomarkers
-CKMB and Troponin I early after CP onset have 34-40% Sn respectively, but if checked late at >12hrs after CP onset, they are nearly 90% Sx
-so best to draw ez at presentation and if + then start Tx if not already started by other Sx/Si. If negative initially, but still likely to be ischemic, then check serial /24 hours
-if low probability of ischemic cause of CP, then DON'T CHECK ENZYMES bc of likelihood of false+
Cardiac Imaging & Stress Testing:
-TTE if H&P/ECG dictate it is needed
-not useful if unconcerning Hx/PE/ECG
-check echo if:
-HCM, sev AS, DCM are possible causes
-possible check if: (but it might look Nl)
-LCAPA - echo--> diastolic flow in ventric septum fr collateral cor arts, retrograde LMCA Q, MR w Nl valve, signif LV syst dysfx
-Cor Art Fistula - echo--> diastolic color flow in chamber getting the cor fistula - RA, enlarged RA and RV w signif L to R shunt, big coronary root
-KD
-Coronary aneurysm
-MRI/CT - eval anomalous cor arts, cor fistulas, cor aneurysm, ostial cor art dz after reimplantation
-Stress Testing
-to unmask mismatch bn DO2 and VO2... ischemia w activity...
-ECG changes- ST depression
-segmental wall motion abNly by echo/MRI
-perfusion defect by nuclear imaging/MRI
-?role of stress testing for pt w poss ischemia...
-it is the most Sn and Sp to assess pt who has Nl heart at rest (w Nl ECG, LV myocardial perfusion/wall motion), Thus change in myocardial pefusion w stress more clearly defines diff bn Nl vs abNl.
-if structurally abNl heart (HCM), or abNl ECG (LBBB) then less able to accurately tell true ischemia
-In pt w nonathersclerotic fixed cor art dz, a negatv stress test might not clearly define pt's ischm risk
-Pts w anom CAD may be ASx w sports/exercise, as stress tests are often Nl
-one study of pts w death w sports w known anomalous coronary artery origin, of the 6 pts w prior stress test, all were Nl!
-Thus, if you want to decide who's best for stress testing, c/s who's should have high index of suspicion after the initial workup, has a Nl heart structure (bc test not accurate otherwise), and are able to cooperate with the test
-Type of stress test- nuclear vs echo, d/o institutional preference
Tx:
-Immediate Tx for ischemic pt in CP:
-decr VO2: beta-blocker, antipltlt Rx
-Dx test to check cause
-definitive Tx
-if h/o KD, and pt in CP w ischemic ECG--> Tx like a typical acute MI - antithrombotic Tx vs immediate cath w perQ cor intervention
-surgical Tx if anomalous cor art origin...
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