A premature ventricular complex (PVC) is an abnormal heartbeat caused by an ectopic focus in the ventricles. In this segment of 'Simplified in Practice', we will be discussing what causes PVCs and how to determine their ECG features.

---

A premature ventricular complex (PVC) is also referred to as ventricular ectopics, ventricular extrasystoles, ventricular pre-beats, and ventricular pre-depolarisations.

ECG characteristics of PVCs

• A broad QRS complex with aberrant morphology (120 ms)
• Premature - i.e. happens sooner than the following sinus impulse would be anticipated
• Discordant alterations in the ST segment and T wave
• Usually immediately followed by a complete compensating pause
• The capture of the atria retrogradely may or may not occur

---

Ectopic beats: What causes them?

Ectopic impulses from subsidiary pacemakers are generally blocked by faster impulses from above. However, if an ectopic focus depolarises early enough before the arrival of the following sinus impulse, it may "catch" the ventricles, creating atrial (PACs), junctional (PJCs), and ventricular (VV) ectopic contractions.

---

Basis of ECG findings

1. The His-Purkinje system is bypassed, and the ventricles are depolarised directly as a result of ectopic ventricle firing.
2. This alters the usual cardiac activation sequence, resulting in erratic activation of the two ventricles.
3. As a result of the resulting interventricular conduction delay, QRS complexes with extended length and aberrant shapes are formed.
4. PVCs are considered "frequent" if they occur more than five times per minute on the ECG, or more than ten to thirty times per hour during ambulatory monitoring.

---

Reasons

PVCs that occur often or are symptomatic may be caused by:

1. Anxiety
2. Sympathomimetic drugs
3. Beta-agonists drugs
4. Myocardial ischaemia
5. High caffeine
6. Hypokalemia
7. Hypomagnesaemia
8. Digoxin toxicity

---

Categories

PVCs may be classified as follows:

1. Unifocal - each PVC is similar and arises from a single ectopic focus.
2. Multifocal - caused by the coexistence of two or more ectopic foci; various QRS morphologies.

The QRS morphology may reveal the origin of each PVC:

1. PVCs emerging from the right ventricle exhibit morphology similar to that of a left bundle branch block (dominant S wave in V1).
2. PVCs emerging from the left ventricle exhibit the shape of a right bundle branch block (dominant R wave in V1).

PVCs are often seen in recurring patterns:

• Bigeminy- Each subsequent beat is a PVC

• Trigeminy- Each third beat consists of a PVC
• Quadrigeminy- Each fourth beat consists of a PVC

• Couplet- Two PVCs in succession

• NSVT- A series of three to thirty successive PVCs

Definitions differ in about three or more PVCs. Some sources refer to this as a triplet of PVCs, while others refer to it as a 'short burst of VT', but more generally as NSVT.

---

Significance in the clinical setting

1. PVCs are a common electrophysiological phenomenon that usually does not require investigation or treatment.
2. Frequent PVCs may cause palpitations and a sensation that the heart is "skipping a beat".
3. In patients with pre-existing predispositions (e.g. ischaemic heart disease, WPW), a PVC may precipitate the initiation of a re-entrant tachydysrhythmia, e.g. VT, AV.

Generally, frequent PVCs are benign, unless in the presence of a prolonged QTc, when they may lead to malignant ventricular arrhythmias such as Torsades de Pointes by creating the "R on T" phenomenon.

---

Click here to see references

Disclaimer- The views and opinions expressed in this article are those of the author's and do not necessarily reflect the official policy or position of M3 India.

The author is a practising super specialist from New Delhi.