Premature Ventricular Contraction (PVC) Vs Premature Atrial Contraction (PAC)

Fluttering, jumping, pounding, or skipping a beat disturbs us. These are palpitations. These sensations occur due to extra or early heartbeats and are also known as ectopic beats or premature beats.

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Abnormal heartbeats

When the muscles of the heart contract rapidly, we feel as if our heart is racing or jumping. PAC (premature atrial contraction) and PVC (pre-ventricular contraction) are two such conditions causing abnormal heartbeats. 

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Ectopic or abnormal heartbeats are harmless and do not occur because of a heart problem or health condition. The heart functions normally and may beat out of rhythm rarely. These beats do not require treatment, but you may need to consult your healthcare provider if you have a 

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• heart condition

• if your heart beats out of rhythm often

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What are the types of ectopic or abnormal heartbeats?

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There are two main types:

• Premature atrial contractions, PAC, occur when signals arise abnormally from the two upper chambers- atria of the heart.

• Premature ventricular contraction, PVC, occurs when abnormal signals come from the two lower chambers of the heart, ventricles.

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Who all experiences abnormal heartbeats?

They can occur in any age group but are common in older adults . Children who have abnormal heartbeats usually have PAC. These abnormal beats occur if one has

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• Family history of ectopic heartbeat

• Heart valve disease

• A history of heart attack

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Other factors causing them are

• Alcohol and caffeine drinks 

• Foods that have more fat, sugar, or carbohydrate content

• Stress and anxiety

• Dehydration 

• Nasal decongestants in use 

• Obesity 

• During menopause and pregnancy

• Smoking

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An ectopic heartbeat arises as a result of a heart problem or health condition like

• Atrial fibrillation and tachycardia.

• Coronary heart disease and heart failure.

• Chronic obstructive pulmonary disease.

• Structural heart problems.

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Symptoms of ectopic heartbeat

Symptoms may not be perceptible to all, while others may feel them lying down. One may feel

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• Skipping a heartbeat or stopping for a moment.

• The heart is speeding up and slowing down.

• Pounding or fluttering in the chest.

• A racing heartbeat.

• Dizziness

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Premature Atrial Complex (PAC)

Premature atrial complex is a premature beat arising from ectopic pacemaking tissue in the atria. An abnormal P wave followed by a normal QRS complex is atrial ectopic, atrial extrasystoles, atrial premature beats, and atrial premature depolarisations.

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Classification of PAC

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PAC may be of 2 types

• Unifocal: It arises from a single ectopic focus. And each PAC is identical.

• Bifocal: They arise from two or more foci. They have multiple P-wave morphologies.

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Recurring patterns in PAC

• Bigeminy: Every other beat is a PAC

• Trigeminy: Every 3rd beat is a PAC.

• Quadrigeminy: Every 4th beat is a PAC.

• Couplet: 2 consecutive PAC.

• Triplet: 3 consecutive PAC.

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Clinical significance of PAC

PAC is a normal electrophysiological phenomenon and does not require investigation or treatment. Frequent PAC causes palpitation a sense of the heart skipping a beat. In patients who already have heart conditions like left atrial enlargement and ischemic heart disease, a PAC causes 

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• Atrial fibrillation

• Atrial flutter

• Tachycardia that may be of the following types, AV nodal re-entrant tachycardia (AVNRT) or Atrioventricular re-entrant tachycardia (AVRT).

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Causes of PAC

Symptomatic PAC occurs due to

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• Anxiety.

• Excess caffeine

• Hypokalaemia

• Hypomagnesaemia

• Digoxin toxicity

• Myocardial ischemia

• Sympathomimetics and Beta Agonist.

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ECG characteristics of premature atrial contraction

• Abnormal P wave morphology. The P wave originates outside the sinus node and is followed by a QRS complex <120 ms.

• Post extrasystolic pause. If a PAC depolarises, the SA node. It resets its rhythm, leading to a longer than usual interval before the next sinus beat.

• Variable conduction patterns. PAC can be conducted normally, abberently, as with a right bundle branch block or maybe non-conducted. In non-conducted PAC, the P wave pattern remains visible, even without a subsequent QRS complex.

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Aberrancy and Blocked PACs

PACs occur early in the cycle and are conducted aberrantly, with a RBBB morphology (the right bundle branch has a longer refractory period than the left). They are distinguished from PVCs by the presence of a preceding P wave.

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PACs that arrive early in the cycle may not be conducted to the ventricles at all. Hence, we see an abnormal P wave not followed by a QRS complex (“blocked PAC”) instead, a compensatory pause as the sinus node resets follows it.

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Premature atrial contraction (PAC): ECG Review

PAC occurs when the focus in the atrium, not the SA node, generates an action potential before the next scheduled SA node action potential.

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The four main characteristics are

• Premature and occur earlier than expected if measured against P-P intervals.

• Ectopic beats originate outside the SA node, causing P wave morphology to be different from the normal sinus P wave.

• PACs typically produce narrow QRS complexes as they originate in the atrium and follow the normal conduction pathway through the AV node. In contrast, PVCs generate wider complexes since they bypass the normal conduction system. However, in some cases, PAC may conduct apparently with a right or left bundle branch block pattern, making differentiation from PVCs mode challenging.

• A compensatory pause occurs when a PAC renders the SA node refractory, causing it to skip its next scheduled beat. As a result, the rhythm resumes exactly two P-P intervals after the normal sinus speed.

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Every other QRS complex is a premature atrial contraction. The rhythm is atrial bigeminy. 

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Premature Ventricular Complex: PVC

Premature ventricular contractions occur when the lower chamber of the heart, the ventricle beats prematurely. ECG shows this as an early wide and bizarre-looking QRS complex that does not have a P wave. A compensatory pause often follows it. Let us see how PVC looks on ECG. 

Symptoms and causes of PVCs 

• A fluttering feeling in the chest 

• Pounding or jumping heart rate 

• Skipped beats and palpitations 

• An increased awareness of your heartbeat.

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The SA node controls sinus rhythm; from here electrical impulses travel across the atria to the ventricles, pumping blood to our lungs as normal sinus rhythm. Ventricles contract earlier than the next expected heartbeat and disrupt the heart’s normal rhythm, causing PVC.

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The premature beat is followed by a stronger contraction making a sensation of a skipped beat or flutter. These extra beats are generally less efficient in pumping blood to the body.

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Some important causes that trigger PVC are

• Heart diseases interfere with normal electrical impulses.

• Chronic obstructive pulmonary disease, COPD, or Pneumonia: when the oxygen supply in the blood is low.

• Medications like decongestants.

• High blood pressure.

• Alcohol.

• Anemia

• Tobacco.

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Diagnosing Ectopics

PACs vs. PVCs are diagnosed during an ECG or by the Holter monitor, a portable device worn for some time when it captures abnormal heart rhythms.

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Prevention and Treatment

PVCs and PACs in the healthy heart are harmless and Do not require any treatment. They can often be kept under control by lifestyle changes such as limiting. 

• Caffeine

• Tobacco

• Alcohol

• Stress

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PVC that occurs regularly requires medications like beta blockers and calcium blockers. For severe cases, catheter ablation may be recommended. During catheter ablation, radio frequency energy cauterizes the area where the ectopic originates.

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What is the Difference Between PAC vs PVC?

Both PAC and PVC are the premature heart beat originating at different locations in the heart. Both cause symptoms like palpitations or a skipped beat, though the severity differs.

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• The difference lies in their point of origin. PVC originates from the ventricles and PAC from the atria.

• Symptoms are more forceful in PVC than in PAC.

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Solitary PVC vs. PAC are benign. Frequent PVC and PAC indicate an underlying condition depending on the frequency, pattern, and overall health.

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Conclusion

You may have been astounded by the statement; my heart skipped a beat. Nevertheless, it is too true to be ignored. Once in a while, it may not warrant attention, but an increased frequency could indicate an underlying health condition.