True Posterior Wall MI ( role of mirror image , vectorcardiography and echocardiography )
An Answer to ECG Case Challenge !!!
69 year old man with substernal chest discomfort. BP 70 mm Hg. History of HTN.
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What is diagnosis ?
1- Acute Inferior wall MI
2- Acute Inferior MI + Reciprocal changes in V1 and v2
3- represent anterior subendocardial injury
4- posterior subepicardial injury.
5- all could be possible
6- none .
The ST-depression in V1 and V2 can be reciprocal change, represent anterior subendocardial injury; OR (as is the case here) posterior subepicardial injury.
In the setting of inferior wall MI (IMI), the ST segment depression seen in Leads V1 and V2 in this patient’s ECG can be merely reciprocal or…
Just By one move you can diagnosis it easily , turn it upside-down and see the left image as a STEMI , but this time , the anterior leads can act as a mirror of posterior aspect of heart , because in standard 12-leads ECG there is not specific lead for Posterior wall of heart . its similarly the dark side of the Moon .
This pattern called mirror image of “mirror-image “ pattern of acute anterior MI ;indicator of True posterior wall MI (if occurred purely just in leads V1 and v2 ) .
The term PMI is used for necrosis of the dorsal, infraatrial part of the left ventricle located beneath the atrioventricular sulcus. The majority of patients with the typical electrocardiographic abnormalities for PMI have a stenosis or occlusion of the RCX. Some patients have a stenosis or occlusion of the RCA. In 10% of the population the RCX is the dominant vessel. It is the least commonly infarcted coronary artery. PMI has been reported to represent 15 to 21% of acute MI, often accompanied by inferior and/or lateral MI. A strict and true PMI is thought to be very rare; however, a more recent study showed an incidence of 3.3% using posterior leads. Risk factors, clinical presentation and differential diagnosis are no different than with other myocardial infarctions.
Goldberger described a characteristic voltage drop-off pattern ( decreased amplitude of R waves ) in v5 and v6 in true posterior MI which is probably due to lateral wall extension .
thus in acute true posterior myocardial infarction , lead v1 shows the “mirror-image “ pattern of acute anterior myocardial infarction namely , the anterior QRS displacement reflected by an increase in the R-S wave ration , an upright T wave and ST-segment depression , placement of posterior chest leads (v7 through v9) can occasionally show diametrically opposite changes to v1 , ( ie, Q waves , ST segment elevation and T wave inversion .
The term “posterior infarction “ in the older ECG literature was used to denote what is now called “inferior or diaphragmatic MI “ . the term true posterior infarction ( also known as “high posterior” “strictly posterior “ ‘Pure posterior” “posterobasal, inferobasal, or dorsal paravertebral “) refers to involvement of the posterior aspect or infra-atrial part of the left ventricle adjacent to the atrioventricular groove . Although true posterior myocardial infarction can occur as an isolated lesion , it often occurs in association with diaphragmatic or lateral infarction .
The occurrence of tall R wave and shallow S waves in leads v1 and v2 is noted as posterior MI with or without ST segment and T wave changes , depending on the stage of the infarction , which points to a lesion in the true posterior aspect of the left ventricle .
Because of the absence of Q waves , true posterior MI is a commonly overlooked ECG abnormality . Vectorcardiography is considered to be more decisive than scalar ECG in the diagnosis of true posterior MI , but even Vectorcardiography has difficulty in differentiating true posterior MI from right ventricular hypertrophy or normal anterior loop variants .
The differentiation of posterobasal myocardial infarction (PMI) from either right ventricular hypertrophy (RVH) or normal subjects displaying an anterior loop (AL) by electrocardiography (ECG) or vectorcardiography (VCG) is difficult.
The presence of a prominent R wave in the right precordial leads of the ECG frequently creates a clinical dilemma. In the adult a distorted anteriorly directed vector may occur in posterobasal infarction as a result of loss of posterior forces, in right ventricular hypertrophy as a result of increased anterior forces and in at least 20% of normal in- dividuals.
. criteria for diagnosing posterior Myocardial infarction ;
1- *An R wave duration of 0.04 s in leads v1 and v2 with upright T wave and in the acute phase ST-segment depression .
2-* ST segment Depression (Horizontal >> downsloping /upsloping)
3-* Prominent R wave and Upright T wave
4- *Combination of Horizontal ST segment depression with upright T wave
5- Coexistent Acute Inferior and /or Lateral MI
6- Additional ECG leads (posterior leads V7 to V9) ≥ 1mm ST segment Elevation
7-* An R-S wave ratio of one or more in leads V1 or v2.
8- No pathologic Q wave in the standard 12-leads ECG , unless diaphragmatic or lateral infarction coexists .
9- A Q wave duration of 0.04 s in an area posteriorly between the spine and the left scapula .
10- *Slurring of the descending limb of the R wave in lead V1.
Differential diagnosis of Tall R wave in lead V1
once you see the tall R wave in lead V1 remember these 14 points ;
1- True Posterior MI
2- Right ventricular Hypertrophy
3-Ventricular Septal hypertrophy
4- Duchenn’s dystrophy
5- Right bundle Brunch Block
6- wolf-parkinson white syndrome
7- Rightward Cardiac displacement
8- misplacement of precordial leads
10- in children
`12-Congenital heart disease
14-ventricular ectopic impulse