You Ask I Find The Answer-ECG Interpretation: Infarction-Injury Part IIIa

Infarction

Myocardial Infarction Triad

Injury

(means acute or recent)

Injury indicates the acuteness of an infarct. Elevation of the ST segment denotes "injury" sometimes called the "current of injury".

The ST segment is that section of baseline between the QRS complex and the T wave. The ST segment contains.

Elevation of the ST segment signifies "injury". The ST segment may be elevated only slightly, or as much as one or more milimeters above the baseline.

ST segment elevation tells us that a myocardial infarction is acute. It is the earliest consistent sign of infarction to record on EKG.

Angina with exertion, "Prinxmetal's angina, can cause transient ST elevation in the absence of an infarction.

ST Elevation

If there is ST elevation, this indicates that the infarction is acute. ST elevation, alone, can indicate an infarction.

Once you have made a diagnosis of infarction, it is important to know whether the infarction just occurred and needs immediate treatment, or if the infarction is old, maybe years old.

The ST segment rises above the baseline with an acute infarction, in fact it is usually the earliest EKG sign of an infarction. With time, the ST segment returns to the baseline. 

If the ST segment is elevated without associated Q waves, this may represent non-Q wave infarction, which is usually a small infarction that may herald an impending larger infarct. Significant ST changes require enzyme studies and close scrutiny.

A ventricular aneurysm (the outward ballooning of the wall of ventricle) can cause persistent ST elevation in most of the chest leads; but in this case, the ST segment does not return to the baseline with time. Pericarditis (next page) produces a unique type of ST segment elevation that may also elevate the T wave off the baseline.

Brugada Syndrome-ST Elevation

RBBB pattern QRS with ST elevation in V1-V3

Can cause sudden cardiac arrest (in absence of coronary obstruction)

Brugada syndrome is a hereditary condition that can cause sudden death in individuals without heart disease. It is characterized by Right Bundle Branch Block with ST elevation in leads V1 to V3. Look for it; this malady is not rare.

Sudden cardiac death (cardiac arrest ) can occur spontaneously in patients with Brugada syndrome.

In Brugada syndrome there is RBBB and ST elevation in leads V1 to V3. The elevated ST segments have a peculiar, peaked downsloping shape, particularly in V1 and V2.

Brugada syndrome is a familial condition caused by dysfunctional cardiac Na+ (sodium) channels. Prophylaxis against the deadly arrhythmias requires ICD implantation in order to immediately treat cardiac arrest (usually ventricular fibrillation). 

This syndrome is responsible for nearly one half of the sudden deaths in healthy young individuals without structural heart disease.

Pericarditis-ST Elevation

With pericarditis, the ST segment is elevated and usually flat or concave. The entire T wave may be elevated off the baseline. 

Pericarditis is inflammation of the membrane (pericardium) that surrounds the heart. Pericarditis may be caused by a virus, bacteria, cancer, or other sources of inflammation, including myocardial infarction.

Pericarditis can elevate the ST segment. It usually produces an elevated ST segment that is flat or slightly concave (middle sags downward). This resolves with time.

Pericarditis seems to elevate the entire T wave off the baseline; that is, the baseline gradually angles back down (often including the P wave) all the way to next QRS.

The characteristics shown in the left illustration are found in lead in which the QRS is usually mainly negative (like the right chest leads). The pattern shown in the right illustration is seen in leads where the QRS is mainly positive (such as the lateral and inferior limb leads). Sometimes PVC's are produced.