12-Lead ECG case: A tale of too many Q waves
Review the findings for a critical shock patient and understand the ominous implications of pathological Q waves
An 88-year-old woman was brought to the emergency department by paramedics. She was hypotensive and weak. She was able to answer questions with brief answers. Her breath sounds were decreased in the bases. She had been sick for about four days without calling for help, and was found by someone on the fifth day very ill. This is her ECG.
The findings on this ECG include elevated, flat-topped or domed ST segments in V2 through V6. Sometimes called tombstone ST segments, these are in the anterior wall, in the area supplied by the left coronary artery’s anterior descending branch (LAD). Other notable findings include:
- Pathological Q waves in V2 through V6. Pathological Q waves indicate necrosis of the myocardium, which is usually permanent.
- ST elevation and flattening in Leads I and aVL, which indicates high lateral wall injury. This is the area of the LAD and the left circumflex artery.
- Pathological Q waves in II, III and aVF. More necrosis, but this time the ST segments are not elevated. This is the inferior wall, usually supplied by the right coronary artery (RCA).
- ST segments convex upward — frowning — in II, III and aVF. These indicate ST elevation which is resolving.
What does the ECG tell us?
This patient is having an acute anterior-lateral wall MI. Further, the pathological Q waves tell us that hours have passed since the onset of the blockage and there has been irreversible damage to the anterior wall. Picture that area of her heart not contracting at all. In addition, her inferior wall has pathological Q waves, which means more necrosis, no contraction and abnormal ST segments.
Are pathological Q waves an important EMS finding?
Remember, pathological Q waves signify necrosis. ST elevation indicates injury. Injured tissue contracts poorly because of stunning. Dead tissue does not contract at all.
So, it is not surprising that this patient presented in shock. It is easy to recognize that this is cardiogenic shock caused by pump failure, not hypovolemia. The patient is hypotensive and hypoperfused. What do you think a fluid bolus would do to her?
Do pathological Q waves indicate an old MI?
They can. Unlike ST elevation, pathological Q waves in the left ventricle rarely go away. They remain as a scar or injury on the heart for life.
When we see pathological Q waves with normal ST segments and T waves, the acute phase is over. When the Q waves are accompanied by ST elevation, we know this is an acute MI that has, unfortunately, developed necrotic areas.
Of course, the clinical findings help tremendously. Remember, this patient was sick for four days and then got worse. She most likely had the inferior wall MI four days ago, and then today had the anterior wall MI.
What causes the Q waves on the ECG?
Some leads have a normal Q wave, which indicates the septum depolarizing from left to right, and slightly ahead of the rest of the ventricular muscle. The rest of the QRS complex is comprised of a combination of forces in the left ventricle — right to left — and the forces in the right ventricle — left to right. The ECG machine combines information from the two ventricles to produce a QRS that is mostly influenced by the large left ventricle.
When part of the left ventricle is killed, the dead cells no longer depolarize. Electronically, that area becomes a dead "hole" in the heart. The ECG electrode positioned over the dead zone would have normally seen depolarization waves coming toward it — now it sees nothing from that area, as if it is looking through a hole.
The ECG machine will record the forces on the other side of the heart, unopposed by the tissue that is dead. In other words, the dead area is removed from the equation. The forces from the opposite side of the heart produce a negative deflection — a pathological Q wave. Areas that have pathological Q waves have a full-thickness injury that has resulted in necrotic tissue which does not depolarize, conduct or contract.
Pathological Q waves are:
- Wider than 1 mm which is 1 little block or 40 ms.
- More than 2 mm deep which is 2 little blocks.
- 25 percent or more of the total vertical size of the QRS.
- Seen in leads V1 through V3 since these leads never have a normal Q wave.
Q waves that look pathological may be seen in Leads III and or aVR as a normal variant.
What happened to the patient?
She was quickly taken to the cath lab. The findings on the patient’s cardiac cath were:
- 100 percent occlusion of the proximal LCA, at the bifurcation of the circumflex artery. Anterior-lateral MI.
- Occlusive lesion of the RCA that had spontaneously reperfused after the clot dissolved over time, indicating inferior wall MI that occurred several days ago.
The patient suffered cardiac arrest during the procedure and was resuscitated. Her LCA was opened and she was admitted to the cardiovascular ICU on balloon pump support. Sadly, she died approximately three hours later.
In this case, the huge number of pathologic Q waves are an ECG sign of necrotic tissue over a very large percentage of the myocardium. Dead tissue does not contract. Overwhelming pump failure — cardiogenic shock — is rarely survivable.
Our goal is to prevent the formation of pathological Q waves by getting patients to intervention as quickly as possible. Time is muscle. It is just as important for EMS providers to educate people about the importance of calling 911 when they have cardiac symptoms.