A 64-year-old male with a past medical history of atrial fibrillation on rivaroxaban (but not taking rivaroxaban for the past one week), myocardial infarction with multiple prior stents placed, heart failure with reduced ejection fraction, and hypertension presents to the emergency department (ED) with palpitations, dizziness, chest pain, and shortness of breath since 5:00 PM. At the time of initial assessment, the patient reports that his dizziness, chest pain, and shortness of breath have greatly improved since earlier tin the day and nearly resolved, though he is still having palpitations. An ECG is obtained immediately upon his arrival (Figure 1).
Interpretation:
Rate: 85 bpm; Rhythm: irregular rhythm; Axis: normal axis Intervals: PR: unable to calculate;
QRS: 99, normal; QTc: 432, normal; P-Waves: not present; QRS Complex: normal; ST Segment/T-
waves: 2 mV ST elevation in lead V4, 1 mV elevation in lead V5
Shortly after the initial evaluation, the nurse notices a new heart rate on the cardiac monitor, and a second ECG is obtained (Figure 2).
Figure 2. Repeat ECG.
Interpretation:
Rate: 227 bpm; Rhythm: regular ; Axis: extreme/NW axis Intervals: PR: unable to calculate;
QRS: 251 wide; QTc: 381, normal; P-Waves: not present; QRS Complex: abnormal; ST Segment/T-
waves: unable to calculate
The new ECG is concerning for ventricular tachycardia (VT). The patient remains hemodynamically stable, so the decision was made to treat with amiodarone 150 mg IV. However, prior to administration, the patient spontaneously cardioverted back to atrial fibrillation and was admitted to the Cardiac ICU.
Discussion:
What is the rate of VT, and why is that so important?
Rate 20-40 bpm: ventricular escape rhythm (VER)
Rate 40-120s bpm: accelerated VER or accelerated idioventricular rhythm (AIVR)
AIVR is usually associated with myocardial reperfusion. It can also be due to digoxin toxicity or cardiac ischemia. If you see a run of AIVR in a patient with a story for acute coronary syndrome, you should consult cardiology for possible catheterization.
AIVR is transient and self-resolving. It should not cause hemodynamic instability.
Differentiating AIVR from VT is important (i.e. check the rate and if it’s sustained) because treatment of AIVR with lidocaine, amiodarone, or procainamide can cause asystole.
Rate >120s -130s bpm: ventricular tachycardia (usually >140 bpm but can be as low as 120 bpm)
How does VT with a rate of 120 bpm happen? What are the three mechanisms that cause VT?
Re-entry (the most common)
Typically, a Purkinje fiber divides into two branches, and when the impulses from both branches meet, they cancel each other out. Re-entry happens when one of the pathways develops a conduction block due to myocardial scarring, often caused by ischemia or a previous infarction. This block allows a ventricular impulse from the normal pathway to re-enter the blocked region, forming a re-entry circuit (Figure 3).
Triggered activity
Due to after-depolarizations, which are abnormal depolarizations that occur during or after a normal action potential during the repolarization phase.
If the amplitude of the after-depolarization reaches the threshold potential, it initiates a new action potential, leading to a triggered activity (Figure 4).
Examples include Torsades de Pointes and digoxin toxicity.
Abnormal automaticity
This happens when a cluster of cells in the ventricle, outside the heart's normal pacemaker, spontaneously fire at a rate faster than that of the sinus node.
It can be triggered by ischemia, reperfusion, inflammation (such as myocarditis), or electrolyte imbalances (especially potassium).
How could you tell that the ECG in Figure 2 was VT despite the slow rate?
Begin by determining whether the rate is regular or irregular. If you have a regular wide-complex tachycardia, VT should be considered.
ECG features that suggest that the regular wide-complex tachycardia in Figure 2 is VT:
QRS: QSR >120 is considered wide, a QRS >160 favors VT.
Note: Beware a QRS >200, this could be suggestive of toxicologic and metabolic VT mimics.
AV Dissociation: This occurs when the atria and the ventricles beat independently of each other, which may lead to fusion beats and capture beats.
Fusion beat: This occurs when a normal supraventricular impulse and an abnormal ventricular impulse simultaneously activate the ventricles, leading to a QRS complex with a morphology that is intermediate between the two (Figure 3).
Capture beat: This occurs when a sinus impulse travels through the AV node and depolarizes the ventricles (effectively capturing the ventricles), resulting in a QRS complex of normal duration, occurring between wide QRS complexes in the context of AV dissociation.
Figure 3. Fusion beats (Life In The Fastlane).
Extreme axis deviation (or NW axis): Look for negative QRS complexes in leads I and aVF.
Atypical QRS morphology: Lack of classic RBBB or LBBB morphology.
Josephson’s sign: Notching near the nadir of the S wave is seen in leads II, III, aVF.
Positive or negative concordance: Uniform direction of QRS complexes across all precordial leads (either all positive or all negative) is concerning for a ventricular origin.
What if the wide-complex tachycardia has an irregular rhythm?
An irregular wide-complex tachycardia could be many things, one of which is polymorphic VT. In polymorphic VT, there are multiple ventricular foci with the QRS complexes that vary in amplitude, axis, and duration. The two subtypes include:
Torsades
Bidirectional VT (seen in digoxin toxicity)
Typically, these QRS complexes are of varied amplitude, axis, and duration.
How is VT treated?
The first step, always, is to determine whether the patient is stable, unstable, or pulseless.
Pulseless: ACLS
Unstable: Synchronized cardioversion
Stable: Amiodarone vs Procainamide vs Lidocaine
Torsades: Magnesium
Authored by Taylor Wahrenbrock, MD; Michael Hohl, MD; and Ari Edelheit, MD.
References:
LITFL Monomorphic VTach: https://litfl.com/ventricular-tachycardia-monomorphic-ecg-library/
ECG Weekly VT: https://ecgweekly.com/ecgstat/ventricular-tachycardia-vt/
IBCC Ventricular Arrythmias: https://emcrit.org/ibcc/storm/