Electrocardiography (EKG/ECG) is the cornerstone of arrhythmia detection. Among the many rhythms identified, two patterns stand out for their very different clinical implications:
Premature Ventricular Contractions (PVCs): Common, often benign extra beats that can sometimes indicate underlying heart problems.Premature Ventricular Contractions (PVCs)
What are PVCs?
PVCs are extra heartbeats originating from the ventricles rather than the sinoatrial (SA) node. They occur earlier than expected in the cardiac cycle, interrupting the regular rhythm.
PVCs are common and may be found in healthy individuals, but frequent PVCs or specific patterns can indicate risk of ventricular tachycardia or fibrillation.
EKG Features of PVCs
- Rate: Depends on underlying rhythm
- Rhythm: Regular, interrupted by premature beats
- P wave: Visible normally, but may be absent during PVCs
- PR interval: Slower than normal but within 0.12–0.20 sec
- QRS complex: Wide, sharp, and bizarre during PVCs
Key Sign: PVCs appear as wide, abnormal QRS complexes that occur earlier than expected.
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Causes of PVCs
Cardiac causes:
- Heart failure
- Myocardial ischemia or infarction
Drug-related causes:
- Toxicity (e.g., digoxin)
- Stimulants (caffeine, nicotine, alcohol, cocaine)
- Electrolyte imbalances (hypokalemia, hypomagnesemia)
- Stress or pain
- Increased cardiac workload (exercise, fever, hypervolemia, tachycardia)
Clinical Manifestations of PVCs
- Often asymptomatic
- Sensation of “skipped beat”
- Palpitations or pounding heartbeat
- Dizziness or anxiety in frequent PVCs
- Chest pain (warning sign—especially if associated with ischemia)
R-on-T Phenomenon: If a PVC falls on the T wave (ventricular repolarization), it may trigger ventricular fibrillation, a fatal arrhythmia.
Types of PVC Patterns
- Bigeminy: PVC every other beat
- Trigeminy: PVC every third beat
- Quadrigeminy: PVC every fourth beat
Treatment of PVCs
If asymptomatic with healthy heart: No treatment needed
If symptomatic or frequent:
- Oxygen therapy
- Reduce caffeine, alcohol, or stimulant intake
- Correct electrolyte imbalances
- Adjust or discontinue causative drugs
- Beta blockers or antiarrhythmics in select cases
Clinical Tip: Notify healthcare providers if PVCs increase in frequency, cause chest pain, or occur during the T wave (R-on-T).
Asystole (Flatline)
What is Asystole?
Asystole is the absence of ventricular electrical activity—a flatline on EKG. There is no cardiac output, no pulse, and no oxygen delivery to the body.
It represents one of the most severe cardiac arrest rhythms, with very low survival rates.
EKG Features of Asystole
- Rate: None
- Rhythm: Flat, absent
- P wave: Absent
- PR interval: None
- QRS complex: None
Key Feature: A straight flatline with no discernible cardiac activity.
Causes of Asystole
- Myocardial ischemia or infarction
- Severe heart failure
- Electrolyte imbalances (hypokalemia, hyperkalemia)
- Severe acidosis
- Cardiac tamponade
- Drug overdose (e.g., cocaine, opioids)
- Post-cardiac arrest deterioration
Clinical Manifestations
- Unconsciousness
- Absence of pulse and blood pressure
- No respiration
- Cardiac arrest
Treatment of Asystole
Unlike ventricular fibrillation, defibrillation is not effective in asystole. Treatment focuses on high-quality CPR and advanced life support.
High-Quality CPR Guidelines:
- Hands placed at center of chest (lower half of sternum)
- Arms straight, shoulders above hands
- Compression depth: 2–2.4 inches (5–6 cm)
- Rate: 100–120 compressions/min
- Ratio: 30 compressions to 2 rescue breaths
- Minimize interruptions
Additional Management:
Epinephrine every 3–5 minutes- Hypoxia, Hypovolemia, Hypothermia, Hydrogen ion (acidosis), Hypo-/hyperkalemia
- Tension pneumothorax, Tamponade, Toxins, Thrombosis (MI/PE)
Comparative Overview: PVCs vs Asystole
| Feature | PVCs | Asystole |
|---|---|---|
| Definition | Extra premature beats from ventricles | Complete absence of electrical activity |
| EKG appearance | Wide, abnormal QRS complexes | Flatline |
| Symptoms | Often asymptomatic; palpitations | Unconscious, pulseless |
| Severity | Often benign, but can trigger VT/V-Fib | Universally fatal without immediate CPR |
| Treatment | Correct causes, reduce stimulants, meds if needed | CPR, epinephrine, correct reversible causes |
| Risk | May progress to dangerous arrhythmias (R-on-T) | Immediate death if untreated |
Frequently Asked Questions (FAQ)
Q1. Are PVCs dangerous?
Most PVCs are benign, especially in young healthy individuals. However, frequent PVCs or those associated with heart disease may indicate risk for ventricular tachycardia or fibrillation.
Q2. What is the difference between PVC and PAC (Premature Atrial Contraction)?
PVCs originate from the ventricles and appear as wide, bizarre QRS complexes. PACs originate from the atria and show premature P waves with narrow QRS complexes.
Q3. Can asystole ever be shocked (defibrillated)?
No. Defibrillation works only when chaotic electrical activity (like V-Fib) is present. In asystole, the heart is electrically silent, so shocks won’t help.
Q4. What is the survival rate in asystole?
Survival is very low (<5%), but immediate CPR and correction of reversible causes may save some patients.
Q5. Can PVCs progress to asystole?
Not directly. PVCs can progress to more severe arrhythmias (like V-Tach or V-Fib), which can eventually lead to asystole if untreated.
