Today our topic of discussion is Electrocardiogram for Blocks. An Electrocardiogram (ECG or EKG) is a graphic representation of the electrical activity of the heart. It’s an essential diagnostic tool that can help determine various cardiac conditions, including heart blocks. Heart blocks, also known as conduction disorders, are disturbances in the normal rhythm of the heart due to a delay or failure in the conduction of electrical impulses.
Electrocardiogram for Blocks
Blocks
- Sino-atrial blocks (SA block) occasional long pauses between R-R complexes
- First degree AV block: P-R interval is prolonged beyond 0.20 second
- Second degree AV block (Mobitz type I or Wenckebach): P-R interval is progressively prolonged until finally as QRS complex is dropped.
- Second degree AV block (Mobitz type II): A QRS complex is present after every 2nd, 3rd, 4th P wave.
- Third degree AV block (Complete heart block): P wave, do not have any relation with QRS complexes. In this block, none of the atrial impulses reach the ventricles. Thus, the atria and ventricles beat independently. On an ECG, the atrial rate is regular (from the P waves), and the ventricular rate is also regular (from the QRS complexes), but they are at different rates, with the atrial rate usually being faster. There’s no consistent relationship between the P wave and the QRS complex.
- Bundle Branch Blocks: These can be right or left, indicating which side of the heart’s conduction system is affected. In a right bundle branch block (RBBB), the right ventricle is activated late, causing the QRS complex to be widened (> 0.12 seconds) and usually showing a characteristic ‘rabbit ear’ appearance in the right precordial leads. In a left bundle branch block (LBBB), there’s a broad, monophasic QRS complex in the left precordial leads and a widened QRS complex.
- Right bundle branch block (RBBB): M-shaped QRS complexes in lead V1, V2, QRS complexes measure more than 0.12 second in width and are above the isoelectric line in lead Vi. Broad and slurred S-wave in lead VS and V6
- Left bundle branch block (LBBB): M-shaped QRS complexes in leads V5 and V6. QRS complexes prolonged more than 0.12 second and are below the isoelectric line in lead V1. Deep S-wave in leads VI and V2
- Premature ventricular contractions (PVCS): No P-wave, QRS complexes are wide and bizarre with T-wave in opposite direction
- Ventricular tachycardia: No P-waves, QRS complexes nare wide and bizarre and resemble PVC in succession .
- Ventricular fibrillation: A wavy baseline, no discernable QRS complexes.
- Ventricular asystole-no wave pattern, usually only a flat line present.
Pathophysiology Behind Heart Blocks
The normal electrical pathway of the heart begins in the sinoatrial (SA) node located in the right atrium. From here, the impulse travels down through the atria to the atrioventricular (AV) node, and then via the bundle of His which bifurcates into the right and left bundle branches, and eventually through the Purkinje fibers to the ventricles. A block can occur at any point in this pathway.
Blockages might be caused by:
- Ischemic heart disease
- Myocarditis (inflammation of the heart muscle)
- Cardiomyopathies (diseases of the heart muscle)
- Medications such as beta-blockers, calcium channel blockers, or antiarrhythmics
- Lyme disease
- Infiltrative diseases such as sarcoidosis
- Degenerative changes with age
Diagnostic Importance of Recognizing Heart Blocks
Diagnosing and understanding the type of heart block is crucial because it dictates management strategies.
- First-Degree Block: Although not dangerous in itself, it can indicate other underlying heart problems. Monitoring and possibly an echocardiogram might be advised.
- Second-Degree Block, Type I: This usually isn’t serious but requires monitoring. If symptomatic (like if causing dizziness or fainting), a pacemaker might be recommended.
- Second-Degree Block, Type II: This can be more unpredictable and may necessitate the implantation of a pacemaker, especially if it causes symptoms.
- Third-Degree Block: This is serious and usually requires urgent pacemaker placement. The ventricular rate, if left untreated, might be too slow to sustain adequate blood pressure or cardiac output.
- Bundle Branch Blocks: These are significant because they can indicate other underlying heart disease, such as previous heart attacks, heart failure, or cardiomyopathy.
Treatment and Management
Treatment depends on the type of block, its cause, and the presence of associated symptoms.
- Pacemaker: A small device placed under the skin, usually in the chest, which sends electrical impulses to start or regulate a slow heartbeat. It’s often used in Mobitz II or third-degree blocks.
- Medication Adjustments: If a heart block is caused by medications, adjusting or stopping the medication, under a doctor’s advice, can resolve the issue.
- Management of Underlying Condition: Addressing conditions like Lyme disease or myocarditis can resolve the associated heart block.
Conclusion
Electrocardiograms are vital in diagnosing heart blocks. Recognizing the characteristic ECG changes can guide timely and appropriate management, potentially saving lives. As technology and medical understanding continue to advance, the precision and capability of these diagnostic tools will only improve, further enhancing the clinician’s ability to care for those with cardiac conditions. Always consult with a cardiologist or healthcare professional when interpreting or diagnosing from an ECG.
Read more: