Faint-hearted at Flinders Street

What are we seeking when we look at an ECG?  We may be looking for normality,  or for findings that confirm or support our clinical suspicion.  Often we find changes that are “non-specific” or else   are clear-cut but are unrelated to the current problem.  Perhaps we should call the latter changes “distractors”.  This case highlights some of these issues.

The patient is a 33 year old man with a past history of bipolar disorder.  He smokes 20 cigarettes per day and intermittently smokes marijuana.  On the day of presentation he shared a “joint” with a stranger at Flinders Street Station.  After two inhalations he blacked out and collapsed to the ground.  An ambulance was called and found that the patient’s initial GCS was 6,  he had pinpoint pupils and an initial heart rate of 170 beats per minute. The patient’s GCS rapidly improved to 15, although he had a short period of visual hallucination.

This is the ECG recorded on arrival.

Right axis deviation is present
A S1S2S3 pattern is present
A S1Q3T3 pattern is present
The QRS complexes are widened
Right atrial abnormality is present
The Brugada ECG pattern is present
The early repolarization pattern is present
The QT interval is prolonged

+ Which of the above statements is/are true regarding this ECG?

The answers are:

False; True; False; True; False; False; True; False

+ Describe and Interpret ECG_0013

Sinus rhythm is present with a ventricular rate of 100 beats per minute. The P wave shape is normal and the PR interval is 0.16 seconds Right bundle branch block (RBBB) is present, with a QRS width of 120 msec in most leads and 160 msec in Lead V1. There is J point elevation and slight ST elevation in Lead II and Leads V3 to V6, consistent with the early repolarization pattern. The QT interval is normal.

Leads I - III all have a S wave. This S1S2S3 pattern can be a normal variant but also occurs in RBBB and in right ventricular hypertrophy. Lead III has a small Q wave, but the T wave is not inverted. The ECG has a S1Q3 pattern but not a S1Q3T3 pattern.

We can explain the SIS2S3 pattern by reviewing the normal QRS vector in the frontal plane hexaxial system.

The frontal leads shown in the frontal plane hexaxial system. Normal depolarization of the ventricles produces three sequential vectors: an initial vector (1) at + 135 degrees, a second vector (2) at + 20 degrees and a third vector (3) at - 180 degrees.

Vector 1 depolarizes the interventricular septum and may produce a small Q wave in Lead I. Vector 2 is the vector that depolarizes the ventricular walls. Vector 3 depolarizes the part of the ventricles adjacent to the atria.

The shape and size of the QRS complexes in the frontal leads is determined mainly by vector 2. The ECG deflection caused by vector 3 is usually masked by the ECG deflection produced by vector 2, which is larger and travels in a opposite direction to vector 3.

RBBB delays vector 3, so its ECG deflection is not hidden by that of vector 2. The result is a prominent deflection after the R wave produced by Vector 2. If vector 3 is in the quadrant between ± 180 degrees and + 90 degrees a downward deflection (a S wave) is seen only in Lead I. If vector 3 is in the quadrant between± 180 degrees and - 90 degrees a S wave will be present in all the inferior leads.

We can now return to ECG_0013.

The above figure shows the depolarization vector (A) derived from the shape of the complexes in the initial 0.04 seconds of each QRS complex. This represents a QRS axis of about + 65 degrees (which is a normal axis). A second depolarization vector (B) has been derived from the shape of the complexes in the last 0.04 seconds of each QRS complex. This represents vector 3 that has been discussed earlier.

Suppose there was no history of drug use preceding the collapse, and the case was an unconscious collapse in a young male with an ECG that shows RBBB. There is a hint of a 'saddle back' ST segment in the first complex in Lead V1, and this raises the possibility of Brugada Syndrome.

The ECG changes in Lead V1 and Lead V2 in Brugada Syndrome may resemble those of RBBB, as shown in the following figures.

The figure above illustrates the ECG appearance of type 1, type 2 and type 3 Brugada syndrome. The following ECG (from ecgpedia.org) shows a case of Brugada Syndrome that could easily be mistaken for RBBB.

An example of Brugada Syndrome obtained from ecgpedia.org.

The analysis of the above ECG from ecgpedia.org was: "There is no Type I morphology to be seen on this ECG. There is however a suggestion of a Brugada syndrome ECG by the RSR in V1 and V2 (could also represent Right Bundle Branch Block) with, typically for Brugada syndrome associated ECGs, ST elevation; best seen in V2. RSR with ST elevation and a positive T wave is known as a 'saddle back' ST morphology. This patient received sodium channel blocking drugs to acquire a Type I morphology and the diagnosis. Note that V5 and V6 are placed one intercostal space above V1 and V2 (V1 IC3 and V2 IC3)"