Is reciprocal ST segment changes occur only in STEMI ? Can it occur in UA/NSTEMI ?
Even after 100 years of electro cardiology the electrophysiological mechanism of ST elevation in STEMI and ST depression in Unstable angina is still in the hypothetical stages. One popular theory says that the current of injury as we see as ST segment elevation in surface ECG is actually an illusion. It’s apparently due to constant negative current pushing down the rest of ECG segments. Ironically the concept of reciprocal ST depression in patients who have ST elevation is well debated for over 3 decades and is considered a settled issue. It probably represents , a purely electrical phenomenon where the tail end of the lead picks up the opposite vector. Even as conflicts continue to confront the basic electro physiological concepts management strategies of acute coronary syndromes is witnessing great strides.
Aim
We hypothesized if ST depression occurs as response to ST elevation it’s logic to expect strong ST depressive forces should possibly elevate The ST segments in the reciprocal leads .
In fact we have seen this phenomenon in three distinct clinical situations.
1) ST elevation in posterior leads: Patients who present with isolated ST depression in V1, V2 , V3 and ST elevation in posterior chest leads V7, V8 .These patients were initially thought to have isolated posterior MI. But later the cardiac enzymes were found to be normal indicating no myocardial necrosis echo evaluation revealed wall motion defects in anterior segments rather than in posterior segments. CAG revealed critical LAD disease . This we believe a pure reciprocal ST elevation in the posterior leads to a ST depressive forces in anterior leads.
2) Inferior ST elevation with ST depression in V4- V6 : Few patients who present with infero lateral STEMI later do not evolve into Q MI but as a NSTEMI .The initial ST elevation was found be transient and disappeared much earlier, while the ST depression lateral leads persisted.
3) ST elevation in AVR in high risk unstable angina :As already reported in the literature, we have seen ST elevation in AVR in patients with high risk unstable angina. This was more often observed when there is > 3mm ST depression in V4-V6. The AVR ST elevation possibly represents the reciprocal vector.
Conclusion
ST elevation in certain specific leads in some of the patients with ACS, could be a pure reciprocal electrical phenomenon to dominant ST depressive forces in Opposite leads . And hence ST elevation in the surface ECG during early hours of ACS should be interpreted more cautiously. The sanctity assocociated with ST segment elevation could be opened for debate.
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