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That said, there is no long-term mortality benefit to nitrate administration in STEMI, and current ESC guidelines recommend against the routine use of nitrates, even without RV involvement, except in the setting of hypertension or heart failure. Adequate right ventricular preload is essential to maintaining LV function and systemic perfusion, and medications that decrease venous return and RV filling, such as nitrates, should be avoided in RVI. RVI may result in right ventricular dysfunction, compromising left ventricular filling and cardiac output. Current ESC/ACC/AHA/WHF guidelines define this as the appropriate diagnostic cutoff, except in men under age 30, for whom 1 mm should be used (Table 2). Right-sided chest leads V1R-V6R (Figure 2) can be used to improve diagnostic accuracy for RVI, and ST-segment elevation in V4R ≥0.5 mm is roughly 80% sensitive and specific. On a standard 12-lead ECG, RVI may present with ST-segment elevation in the right precordial leads, most prominent in V1, typically with concurrent inferior ST-segment elevation in the setting of associated posterior MI, however, elevation in V1 may be attenuated or absent due to superimposed ST-segment depression. Autopsy data suggests isolated RVI is both rare and non-fatal. Right ventricular infarction (RVI) typically occurs with concomitant inferior wall MI, most often due to occlusion of the right coronary artery proximal to the acute marginal branch. Thus, while the presence of ST-segment elevation in V7-V9 warrants emergent intervention, its absence should not necessarily preclude it. Notably, concern for ongoing ischemia – as in a patient with refractory angina despite maximal medical therapy – should also prompt immediate catheterization, even with a normal ECG. Leads V7-V9 may therefore have the greatest utility in patients with clinically-suspected MI but non-diagnostic 12-lead ECGs by providing an objective finding to expedite emergent intervention. Per both the AHA/ACC and ESC Guidelines, however, isolated anterior ST-segment depression alone is an indication for emergent cardiac catheterization. The addition of posterior leads V7-V9 (Figure 1) increases ECG sensitivity for posterior MI, and current guidelines consider ST-segment elevation ≥0.5 mm in V7-V9 (≥1 mm for men under age 40) to be diagnostic (Table 1). The predominant 12-lead finding in isolated posterior MI is ST-segment depression ≥0.5 mm in leads V1-V3. The standard 12-lead ECG does not directly assess the posterior wall of the left ventricle, and while posterior MI most commonly occurs with concomitant inferior or lateral infarct, isolated posterior MI may occur in up to 8% of acute circumflex occlusions.
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Fontaine lead has been designed to improve visualization of Epsilon wave in arrhythmogenic right ventricular dysplasia.ST-segment elevation is particularly insensitive as a marker for occlusion of the posterior coronary circulation, and specifically the left circumflex artery. Lewis lead and the newly devised modified limb lead system are useful in enhancing detection of atrial activity. EASI lead system permits derivation of 12 leads from just five electrodes. Lund system with leads on proximal part of limbs have both stability and fair diagnostic value. Mason-Likar modification with limb leads shifted to the torso is popular for exercise testing, though the diagnostic value of the ECG is altered.
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Lead stability is important when the movement of the subject is maximum as in exercise testing. Using five leads gives the option of getting a chest lead in addition to bipolar limb leads, enhancing detection of ischemia during procedures. This can be used to record modified bipolar chest leads as well. Simple three electrode bipolar recording is ubiquitous for monitoring. The need for different types of lead systems in different settings has been emphasised. ECG monitoring is common place in the hospital and even pre-hospital setting.