Deadly 12 Lead ECG Diagnosis: Pulmonary Embolism

Its well known that there are things other than STEMI that stand ready to confound, perturb, and otherwise confuse your clinical impression. Pulmonary embolism (PE)  is one of those things. Massive PE has been linked to all sorts of ECG changes. A recent article printed in the American Journal of Emergency Medicine highlighted some of the ECG features associated with cardiogenic shock:

• The S1 Q3 T3 sign
• qR in lead V1
• T wave inversions in V2-V4
• STE in lead V1
• STE in lead aVR

These problematic ECG signs come as no surprise to fellow ECG enthusiasts. The incomplete right bundle branch pattern + T wave inversion indicate "heart strain" that accompanies large pulmonary emboli, 

Here's a recent prehospital 12 lead concerning for pulmonary embolism: 

Bottom line:

The ECG represents a valuable screening tool. Though its not particularly sensitive or specific for pulmonary embolism, there are definitely patterns that should alert the clinician to an adverse outcomes. In the setting of suspected pulmonary embolism, for example, watch out for:

• Right bundle branch block
• Anterior T wave inversions
• STE in aVR or V1

There's STE in V1 !

EMS responds to the report of a 77 year old male with chest pain. The patient is hypertensive, alert, and hemodynamically stable. Aspirin and nitroglycerin are administered per treatment protocol. A 12 lead ECG is obtained, and the paramedic asks about transport to the closest hospital versus a facility capable of percutaneous coronary intervention...


12 lead ECG



12 lead ECG Discussion

There is a baseline sinus rhythm. The rhythm is regular. Close scrutiny of lead II and V1 reveals the presence of p waves. The ST segments are upright in most leads with the exception of aVR. The QRS duration is slightly prolonged consistent with an interventricular conduction delay. The (1) positively deflected QRS in lead V1 and the (2) lengthened QRS duration suggests the presence of a RIGHT bundle branch block. There is a subtle slurred l S wave in V6 which further corroborates the diagnosis of a right bundle branch block.

The Slurred S Wave

12 lead ECG Interpretation

Sinus rhythm, right bundle branch block, rate of approx 80 beats/min.

Case resolution

The patient was transported to a local facility. Serial ECGs remained unchanged and cardiac enzymes were normal. The patient was discharged to home following an overnight hospital stay and a cardiac stress test.

Syncopation and Strain

EMS is inbound with a 50 yo male patient. The patient reports shortness of breath and diaphoresis. He was feeling a bit lightheaded and passed out for approximately 30 seconds prior to calling 911. The patient denies other trauma or recent illness. The patient has noted some increasing dyspnea on exertion during the past week. The onset of symptoms occurred without warning or provocation. EMS acquires a 12 lead ECG. A nurse onscene advised that the patient was hypotensive and "clammy" following the syncopal episode.

PMHX:
Hypertension
Dyslipidemia
Appendectomy

Vitals: 
BP: 110/70
P: 131
R: 22
Sp02: 95%

12 Lead ECG:

12 Lead ECG Interpretation and Discussion: 
The rate is tachycardic at approximately 140 beats per minute and regular. The RSR' morphology and duration of the QRS complex in V1 suggests the presence of a right bundle branch block. The terminal R wave in V1,  the slurred S wave in V6, and the inverted T waves in aVL and V1 are expected in the setting of a bundle branch block. It is difficult to discern p waves though there may be a retrograde P waves present in leads III and V2. Tachycardia and right bundle branch block suggest the presence of "right heart strain."

Final interpretation:
Supraventricular tachycardia, rate of 140/min. Right bundle branch block. Electrocardiographic evidence of right heart strain.

Emergency department course:
Supplemental oxygen was administered. A bedside echocardiogram revealed a dilated right ventricle. There was no pericardial effusion. A portable chest xray was without any obvious abnormality. The patient received an infusion of unfractionated heparin and underwent multi-detector CT angiography of the chest. The patient was found to have bilateral, segmental pulmonary embolisms.

Pulmonary embolism:
A pulmonary embolism, or "PE", may be extremely difficult to diagnose. Patients present with a wide variety of symptoms, and not all pulmonary embolisms result in persistent vital sign abnormalities. Providers should have a low suspicion for pulmonary embolism in patients with tachypnea, tachycardia, and pleuritic chest pain. Syncope is a concerning complaint and can be effectively evaluated with a 12 lead electrocardiogram. In this case, the syncope resulted from the patient's clot burden. A sub-massive pulmonary embolism can reduce preload and compromise cardiac output.

Syncope? Get the 12 lead! 

A Serial Case

An elderly male patient is transported to the emergency department following a syncopal episode. The patient reported feeling lightheaded, and experienced two witnessed syncopal episodes lasting for several minutes. Symptoms were made worse when standing up. The patient denied chest pain and reported some mild dyspnea. The patient had been in his usual state of health. The patient's medical history is significant for a tibial fracture several months prior.

Vitals:

Afebrile

BP: 72/P

P: 100

R: 24

Sp02: 92%, poor waveform, on NRB

Physical exam:

Pt is diaphoretic and alert.

Lungs are clear bilaterally.

The patient's abdomen is soft and non tender.
No evidence of lower extremity edema.

(Prehospital) 12 lead ECG:

Upon arrival at the hospital, large bore IV access was secured. A FAST (Focused Assessment with Sonography for Trauma) exam revealed no obvious free fluid and no obvious pericardial effusion. The abdominal aorta appeared grossly normal. The patient remained alert and responded to a bolus of IV crystalloid. A repeat ECG was obtained following another pre-syncopal event in the emergency department.

12 Lead ECG Interpretation and Discussion

On the repeat ECG, a sinus rhythm is present. The electrical axis is physiologic. Artifact interferes with the tracing in the inferior limb leads. ST segment elevation is present in aVR, V1, and V2. The ST segments appear horizontal in shape. That particular morphology is concerning for ischemia. While some mild ST segment depression is present in lead I, there are no clear cut reciprocal changes. The evolving changes suggest a septal wall myocardial infarction.

Final Interpretation

Sinus tachycardia, septal ST segment elevation myocardial infarction

(WRONG!)

Case Conclusion

The patient was transported emergently to the cardiac catheterization lab. The patient's coronary arteries were CLEAN and without evidence of disease. An emergent echocardiogram showed a severely dilated right ventricle with concurrent diastolic dysfunction. The clean coronary arteries and echocardiograpghic findings combined point to a massive pulmonary embolism as the cause of the patient's symptoms. Another subtle clue to this diagnosis was the hypoxia that persisted with high flow oxygen administration.

Though not all that elevates is a STEMI, field providers should nevertheless focus on identifying worrisome ST segment changes. The patient's initial ECG was somewhat non-specific. Though close inspection can reveal some slight ST segment elevation of less than 1mm in aVR and V1, it certainly did not meet standardized criteria for STEMI. The second ECG, however, represents a clear-cut evolution. ST segments have become more pronounced (elevated) in the septal leads. The increase in elevation combined with the horizontal plateau of the ST segments in leads V1-V2 suggest an evolving myocardial infarction- or an alternative diagnosis.

The patient presented with a syncopal episode and profound hypotension. Any number of emergent medical conditions can present with those complaints. Pulmonary embolism, internal bleeding, and aortic dissection must be considered in the initial assessment of the hypotensive patient. Unfortunately, there are no "classic" electrocardiographic findings associated with a large PE. That said, the following features can be seen in the setting of a pulmonary embolism.

PULMONARY EMBOLISM ECG FINDINGS

• Sinus tachycardia
• Right bundle branch block or incomplete right bundle branch block
• Deep S wave in lead I, Q wave in lead III, and an interveted T wave in lead III (S1, Q3, T3)
• T wave inversions
• Right axis deviation
• ST segment deviation (depression and elevation)

Sinus tachycardia and right bundle branch block may suggest "heart strain." These are electrical manifestations caused by the right ventricle that is pumping against a greatly increased pulmonary resistance.

The Deceptive Ears of a Rabbit

This particular ECG resulted in a great deal of discussion. Though I don't have the actual details of the patient encounter, its clear that the ECG machine, the paramedic student, the preceptor, and the emergency physician all contest the actual interpretation of the following tracing. ECGs like this one represent fantastic learning opportunities. When confronted with a bunch of squiggly lines and conflicting information, it is imperative to stay focused and proceed through the ECG interpretation in a stepwise fashion. Judging from all of the hashmarks, pen marks, and circles, there wasn't any resolution by the time the paramedics had cleaned their stretcher and left for their station!

1) What's the rate?
2) What's the rhythm?
3) Are concerning ST/T segment changes present?
4) Where are my defibrillator / pacer pads?

12 lead ECG

12 lead ECG interpretation and discussion

The ECG tracing reveals a regular rhythm. Before getting distracted by rabbit ears or conduction delays, it is important to discern whether or not a sinus rhythm is present. P waves are occasionally visualized, but there is simply no fixed PR ratio. The absence of a fixed PR suggests that a high grade block is present. Considering the widened QRS, it is likely that the tracing represents a third degree heart block. Further corroborating that interpretation is the relatively fixed R to R interval. Putting this together: wide QRS + fixed R to R + varied PR interval  = third degree heart block. By definition, a right bundle branch block or left bundle branch block CANNOT be diagnosed in the absence of a sinus rhythm.

The ST/T segments are grossly abnormal. The large QS wave present in leads III and aVF suggest a prior inferior wall myocardial infarction. In addition, there is poor R wave progression across the precordial leads. The R wave is still of decreased amplitude in lead V4. Recall that the R wave should transition to a mostly positive deflection by lead V4. There is minimal ST segment elevation in the inferior leads as well. Though this patient may be suffering from acute ischemia, the presence of a third degree block is requires aggressive management and expeditious transport. This rhythm, in the presence of anginal symptoms, warrants chemical or electrical therapy. Transport to an interventional facility, patient stability permitting, is a good strategy.

Fix the rate first!

Final interpretation

Probable third degree heart block, probable inferior wall myocardial infarction, old anterior wall myocardial infarction