The ECG in RV MI shows relatively short-duration ST segment elevation over the right ventricular wall; it has the following unique features;

a)   the ST elevation in V1>V2 or V3[1]; and spatially projects a rightward anterior vector in the frontal plane. Since most cases show also acute inferior MI, this rightward influence often makes the frontal axis of the ST segment approximate 120^o; the ST_iii > ST_ii

b)   the ST is elevated in leads V3R and V4R[2]. Besides being diagnostic of RV infarction [sensitivity=88%; specificity=78%] ST elevation in V4R independently predicts a higher incidence of pace-requiring AV block, ventricular arrhythmias, cardiogenic shock and a greater in-hospital mortality: 31% vs. 6%[3]

c)   V3R and V4R may also show pathologic Q waves; these respective leads normally register an rS or rSr prime deflection in 99-100% and 91% of cases[4].

d)   Although the enzymes show a diagnostic rise, the ST elevations return to normal without further T wave change

e)   Catheterization will show occlusion in the RCA, if dominant, or in the RV branch of a diminutive RCA

f)    In many cases the function of the right ventricle improves sufficiently quickly to suggest reversible ischemia as opposed to muscle necrosis. In similar fashion the Q waves in V3R and V4R, having appeared sooner than is the case with LV MI, disappear rapidly also, seldom seen after 2 months.

g)   while most right ventricular infarctions show transmural inferior MI, evidence for the latter is occasionally lacking

h)   atrial infarction is seen if 3^o AV nodal block permits scrutiny of the elevated ST_a wave

i)    RV coronary insufficiency during exercise is also suggested by stress-induced elevation of ST in V4R[5] (occasionally V1). In other words, while nonocclusive angina, or stress induced myocardial ischemia in the LV, is expressed as ST depression, nonocclusive ischemia, proximal RCA or RV branch PTCA, and acute RV MI, all uniquely cause ST elevation over the RV, optimally in V4R. Thus the RV does not exhibit a physiologically separable subendocardium

In RV MI the ST elevation in V1 has a dome-like character, while ST is normal or even depressed in V2. In isolated RV MI [i.e. without left ventricular ischemia] the ST elevations in V1-V3 may resemble entirely an acute ASMI, except no Q waves develop and the ST’s rapidly normalize.

The very early appearance of both ST and QS in right precordial leads and their rapid disappearance (generally within 10 hours) make the expression RV ischemia[6] more appropriate than infarction. The literature, trying to explain these RV peculiarities, emphasizes the lower O₂ needs of a ventricle with less myocardial mass, less squeeze of intramural vessels, lower preload and afterload, in which coronary flow takes place in both systole and diastole, with 30% from the left coronary system. But there are other reasons for differential behavior of the two ventricles in the face of ischemia. In 1995 the Antzelevitch group had already[7] noted that there were marked differences between the endocardium and epicardium in terms of a) the impact of cycle length change on action potential [AP] duration, b) the morphologic characteristics of the AP in these two regions which were a function of the strength of the transient outward current [I_to]. In further papers these authors noted that the presence of I_to in a tissue layer rendered it more sensitive to ischemia[8]. Of specific relevance to the subject at hand, the canine right ventricular epicardium was very much more sensitive to ischemia than the epicardium of the left ventricle[9]. The action potential typifying I_to shows a ‘spike and dome’. It is probably no coincidence that the ST elevations seen in the V1 of RV ischemia are described as “dome-like”. Thus the RV is more sensitive to ischemia, shows the classic features of same [ST elevation and Q waves] much sooner. Of signal importance: I_to is maximally expressed at slow heart rates or long cycle lengths, explaining why the bradycardia of AV nodal block is so severe a complication, responding well to RV pacing.