Ventricular arrhythmias: Pathology review

Definitions & Key takeaways

An arrhythmia is any disturbance in the rate, rhythm, site of origin, or conduction of the cardiac electrical impulse. Ventricular arrhythmias are those that originate within the ventricles and have a wide QRS complex on ECG. These two types of ventricular arrhythmias are ventricular tachycardia and ventricular fibrillation.

Ventricular tachycardia can be monomorphic meaning that all the QRS complexes look the same, or polymorphic meaning the QRS complexes are different in each beat. A specific and very dangerous type of polymorphic ventricular tachycardia is Torsades de Pointes, which presents a twisting pattern of QRS complexes. This can rapidly progress to ventricular fibrillation, in which the whole PQRST ECG pattern breaks down completely, leaving just some random undulating waves. This is the most common cause of sudden cardiac death.

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Case study0:00–0:24

Clint is a 19 year old male that’s brought to the emergency department for acute chest pain. Upon examination, you notice that his heart rate is really fast, about 170 beats per minute.
He has a history of depression, and is currently being treated with TCAs. He is otherwise healthy.
A few minutes after arriving, Clint loses consciousness. His ECG shows this.

Physiology0:24–1:25

All right, so based on his presentation and ECG, Clint has some form of arrhythmia. The best way to approach arrhythmias is to one: know what a normal ECG looks like, and two: have a good classification system to narrow down the diagnosis.
To help identify an irregular rhythm, you can look at the morphology of the waveform and make sure that there is a P wave before every QRS complex, and a QRS complex after every P wave.
Now let’s take a look at the heart rate. The resting heart beats at a rate between 60 to 100 times per minute, and each of those beats starts off with depolarization of the sinoatrial node, and so we call it a normal sinus rhythm.
It's also important to know that there is typically a delay in the conduction at the AV node and the Bundle of His, which gives some time for ventricular filling before the ventricle contracts.
On the ECG, this is represented by the PR interval, which should be less than 5 small boxes, or 200 milliseconds. Now, any disturbance in the rate, rhythm, site of origin, or conduction of the cardiac electrical activity is called an arrhythmia.

Arrhythmias1:25–3:00

Arrhythmias could be completely asymptomatic, and be picked up incidentally on an ECG. Arrhythmias can also present with palpitations, which is a sensation of your heart beating too hard or fast, fluttering, or skipping a beat.
Additionally, they may alter cardiac output, causing individuals to present with signs of hypotension and decreased brain perfusion, like dizziness, altered mental status, or syncope.
If an arrhythmia is really fast, the heart muscles now demand more oxygen, and if oxygen supply is not met, then the myocardium suffers from ischemia, which presents as angina.
In people with underlying heart disease, the sudden onset of an arrhythmia can precipitate acute heart failure. Finally, some arrhythmias may also cause sudden cardiac death.
Now, arrhythmias can be classified into those originating from above the ventricles, so supraventricular arrhythmias, and those originating in the ventricles, so ventricular arrhythmias.
In general, what's important to remember for your exams is that supraventricular arrhythmias have a narrow QRS complex because there’s a rapid excitation of the ventricles, which means the arrhythmia is originating above or within the bundle of His.
On the other hand, ventricular arrhythmias have a wide QRS complex because there’s a slower spread of ventricular depolarization.Okay, now the two types of ventricular arrhythmias are ventricular tachycardia and ventricular fibrillation.

Ventricular tachycardia3:00–6:41

Ventricular tachycardia or VT for short originates from an ectopic focus located in the ventricle. The two main subtypes are monomorphic and polymorphic ventricular tachycardia.
On ECG, both appear as wide QRS complexes at a rate ranging between 120 and 200 beats per minute. “Monomorphic” means that all the QRS complexes look the same, and it’s classically a complication of myocardial scarring due to acute myocardial infarction.
On the other hand, “polymorphic” means the QRS complexes have different shapes in each beat, as they come from different areas of the ventricle.
This may occur due to acute myocardial ischemia causing the pacemaker cells to be stressed, and it’s not associated with myocardial scarring.
Another cause of polymorphic VT that is frequently tested in the exams is Brugada syndrome. This is a rare autosomal dominant condition characterized by genetic mutations hitting cardiac sodium channels.
Now, the test question will typically describe a male of Asian descent, whose ECG pattern in V1 to V3 shows pseudo- right bundle branch block with the widened QRS presenting an RSR’ configuration, as well as ST elevations.
Now, some individuals affected may present this ECG pattern and yet be asymptomatic, while others may present symptoms like syncope.
Regardless, they’re all at risk of developing polymorphic VT and sudden cardiac death, so treatment is primarily focused around prevention with implantable cardioverter-defibrillators.
A specific and very dangerous type of polymorphic ventricular tachycardia is known as Torsades de Pointes, which is French for “twisting of the points”.
This is because on ECG, the varied QRS complexes give off the appearance that they’re twisting around the isoelectric baseline.
For your exams, remember that Torsades de Pointes is associated with anything that prolongs the QT interval. This includes diseases with genetic mutations hitting ion channels, most often potassium ones.
Examples of these diseases include Jervell and Lange-Nielsen syndrome, which also causes deafness, and Romano-Ward syndrome, which is not associated with deafness.
A prolonged QT interval can also be due to electrolyte abnormalities and especially hypokalemia, hypocalcemia or hypomagnesemia.
On your exams, look for clinical scenarios that may cause these electrolyte abnormalities, such as someone with diarrhea who loses tons of potassium in their stool, and subsequently develops an arrhythmia.
In addition, many medications can prolong the QT, and this is frequently tested.To help you remember them, think ABCDE - where A is anti-Arrhythmics type 1A, 1C and type III; B is antiBiotics like macrolides; C is for antipsyChotics like haloperidol, olanzapine, and ziprasidone; D is for antiDepressants like tricyclic antidepressants; and finally E for anti-Emetic like ondansetron.
Now, regardless of the cause, remember that Torsade de Pointes must be quickly treated with intravenous magnesium sulfate, as it can rapidly progress to ventricular fibrillation.
In many cases, ventricular tachycardia can progress to ventricular fibrillation or V-fib. High-yield triggers include acute myocardial infarction, heart failure, shock, hypoxemia or hypercapnia.

Ventricular fibrillation6:41–7:32

In ventricular fibrillation, the heart’s muscle fibers start quivering because they’re not contracting at the same time.
On ECG, the whole PQRST pattern breaks down completely and there are no actual QRS complexes, just random undulating waves.
And it's important to be able to recognize this pattern, since this situation is extremely dangerous. Essentially, the heart’s not able to squeeze anymore, so there’s no cardiac output.
As a result, your body, especially your brain, isn’t getting fresh oxygen. That’s why ventricular fibrillation is one of the most common causes of sudden cardiac death, so it must be immediately treated with CPR and defibrillation.All right, as a quick recap...

Review7:32–8:24

An arrhythmia is any disturbance in the rate, rhythm, site of origin or conduction of the cardiac electrical impulse. Ventricular arrhythmias are those that originate within the ventricles and have a wide QRS complex on ECG.
These two types of ventricular arrhythmias are ventricular tachycardia and ventricular fibrillation. Ventricular tachycardia can be monomorphic meaning that all the QRS complexes look the same, or polymorphic meaning the QRS complexes are different in each beat.
A specific and very dangerous type of polymorphic ventricular tachycardia is Torsades de Pointes, which presents a twisting pattern of QRS complexes.
This can rapidly progress to ventricular fibrillation, in which the whole PQRST breaks down completely, and is the most common cause of sudden cardiac death.Okay, back to our case.

Summary8:24–8:54

Clint’s presentation describes palpitations and chest pain followed by syncope, suggesting something is going on with his heart.
On ECG, you see a twisting pattern of QRS complexes, typical of Torsade de pointes. It was probably triggered by the TCAs he takes to treat his depression.
You immediately give intravenous magnesium sulfate, successfully saving Clint’s life. Moving forward, Clint should stop TCAs and switch to another antidepressant.