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Acute M.I. In Patient With Pacemaker

Submitted by Dawn on Wed, 01/04/2017 - 21:07

This ECG is taken from an elderly man who has a history of complete heart block and AV sequential pacemaker. On the day of this ECG, he presented to the Emergency Department with chest pain and shortness of breath. His vital signs were stable and within normal limits. We do not have information about his treatment or outcome.

I don’t see spikes. How do we know this is a paced rhythm? The ECG clearly shows the presence of an AV pacemaker. There are very tiny pacer “spikes”, probably best seen in Leads III, aVF, aVL, and most of the precordial leads. Other ECG signs that this is a paced rhythm are: wide QRS at about .16 seconds (160 ms); abnormal left frontal plane axis; regular rhythm with AV dissociation (there are P waves seen occasionally that have no fixed relationship to the QRS complexes). Also, V6 is negative. That rules out left bundle branch block unless the electrodes are misplaced. There are no capture beats in this strip. The patient appears to be, at least right now, 100% dependent on the paced rhythm.

Why does the presence of a pacemaker make it harder to diagnose an M.I. from the ECG? Wide-QRS rhythms, such as right-ventricular paced rhythms, left bundle branch block, and ventricular ectopic rhythms, usually have “discordant ST and T wave changes”. That is, when the QRS is positive (upright), the ST and T wave are negative. The reverse is also true: when the QRS is negative and wide, the ST and T wave changes are positive (ST elevation). This is not true for right bundle branch block because the conduction delay that causes the widening of the QRS is in the right ventricle, and the ST segment is reflecting the LEFT ventricle’s repolarization. Discordant ST changes can make it difficult to determine from the ECG alone that there is an ST elevation M.I. (STEMI). Diagnosis usually must be made from patient presentation, ECG changes over time, and cardiac enzymes – or more definitively from cardiac angiogram. Pacemakers that produce narrow QRS complexes do not cause discordant ST changes.

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Teaching Series: Acute Anterior Wall M.I.

Submitted by Dawn on Sun, 06/26/2016 - 15:33

Intermittent chest pain. This series of three ECG were taken from a 41-year-old man with a two-week history of intermittent chest pain. At the time of the first ECG, 12:05 pm, he was pain-free. We see a sinus tachycardia at 102 bpm, and has just come under the care of paramedics. There is a very subtle ST sagging and T wave inversion in Lead III, and no other ST changes. He had an uneventful trip to the hospital.

On arrival at the Emergency Department, just before he was unloaded from the ambulance (12:15), he experienced chest pain. An ECG was obtained, which shows ST elevation in V1 through V4, as well as in Leads I and avL. There are reciprocal ST depressions in Leads III and aVF.

The patient was taken into the ED, where his symptoms abated, and a third ECG was obtained (12:19). The third ECG looks very much like the first one. V5 and V6 have T waves that appear flat, or even inverted, but there is some baseline artifact making it hard to see them.

Diagnosis confirmed Based on the patient’s presentation, and the second ECG, he was taken immediately to the cath lab. A 100% occluding lesion with a clot was discovered in the mid LAD. The clot was removed with suction, and the lesion stented. A 40% narrowing was discovered in the RCA.

Repeat ECGs whenever possible This series of ECGs offers a compelling argument for performing repeat ECGs. This can be especially important when symptoms are waxing and waning. Sometimes, a clot can completely occlude an artery, then “float” to another position, allowing blood flow to resume. Sometimes, the artery constricts around the lesion, causing occlusion, then relaxes. Had the rescue crew not repeated the ECG at 12:19, there may have been a delay in this young patient receiving interventional care.

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Recent M.I.

Submitted by Dawn on Wed, 04/20/2016 - 23:07

This ECG is from a 54-year-old woman who had an M.I. one week prior to this tracing. She did not receive interventional treatment, as it was not available where she lived when this happened years ago. Her ECG shows the signs of healing injury, as well as probable permanent damage.

Where was this M.I.? The affected leads are all of the precordial leads (V1 through V6), as well as I and aVL. The precordial leads reflect the anterior and low lateral walls of the heart, and Leads I and aVL show us the high lateral wall. This area is perfused by the left coronary artery, and she had a proximal lesion.

What ST and T wave changes are present? All of the leads listed above show a flattening of the ST segments. While they are no longer elevated (the acute injury is over), they are flat and almost convex upward. This shape is usually abnormal, and it has persisted even though the acute injury is subsiding. The T waves in the anterolateral leads are all inverted. This represents reperfusion of the injured tissue. Whether the offending clot is removed by invasive procedure, thrombolytic drugs, or natural degradation, the tissue that is still alive will reperfuse.

Paced Rhythm With Acute Anterior Lateral M.I.

Submitted by Dawn on Mon, 11/28/2011 - 18:57

We caution students that the signs of acute M.I. (ST elevation) cannot reliably be seen in cases of wide QRS. This is because, in wide QRS situations like left bundle branch block, ventricular rhythms, or right ventricular pacing, the ST segments will elevate in leads with downward QRS complexes, and depress when the QRS is upright. These is called discordant ST changes.

In this ECG, a man in his 60's presented with chest pain. His ECG showed AV sequential pacing, with ventricular pacing from the right ventricle. The QRS is 162 ms in duration. He has ST segment elevation in Leads I, aVL, and Leads V2 through V6.

The ST elevations are more pronounced than expected in this paced patient. But, the real clue here is the ST elevation in Leads I, aVL, and V2 - leads that should have ST depression because of their upright QRS complexes, have elevation! This patient was taken to the cath lab and the left coronary artery wass reperfused and stented. For more information about ST elevation in wide QRS complex rhythms, see this LINK.