Rhythms Associated with Acute Myocardial Infarction

Oct 13, 2025 by wbrum.org 66 views

Introduction

Electrocardiography (ECG) is a crucial diagnostic tool in cardiology, providing valuable information about the heart's electrical activity. In our previous installments, we explored the basics of ECG interpretation, including the normal sinus rhythm and various arrhythmias. In this third part of the series, we will delve into more advanced topics, including pacemaker-generated rhythms, rhythms associated with acute myocardial infarction, fascicular block-induced rhythms, rhythms caused by chamber enlargement, the effects of drugs and electrolytes on the ECG, and miscellaneous rhythms. Additionally, we will provide a comprehensive review of the key concepts covered in this series.

Pacemaker-Generated Rhythms

Pacemakers are small devices implanted in the body to regulate the heartbeat in individuals with abnormal heart rhythms. These devices can generate various rhythms, which can be identified on an ECG. The most common pacemaker-generated rhythms are:

Atrial-paced rhythm: This rhythm is characterized by a regular atrial rate, with a P wave preceding each QRS complex. The P wave is typically narrow and upright in lead II.
Ventricular-paced rhythm: This rhythm is characterized by a regular ventricular rate, with a QRS complex preceding each P wave. The QRS complex is typically wide and notched.
Atrioventricular (AV) sequential pacing: This rhythm is characterized by a regular atrial and ventricular rate, with a P wave preceding each QRS complex. The P wave is typically narrow and upright in lead II, and the QRS complex is typically wide and notched.

Rhythms Associated with Acute Myocardial Infarction

Acute myocardial infarction (AMI) is a medical emergency that occurs when the blood flow to the heart is blocked, causing damage to the heart muscle. The ECG can provide valuable information about the location and extent of the damage. The most common rhythms associated with AMI are:

ST-elevation myocardial infarction (STEMI): This rhythm is characterized by a tall, peaked QRS complex with ST elevation in two or more contiguous leads.
Non-ST-elevation myocardial infarction (NSTEMI): This rhythm is characterized by a normal or slightly elevated ST segment in two or more contiguous leads.
Left bundle branch block (LBBB): This rhythm is characterized by a wide QRS complex with a left axis deviation.

Fascicular Block-Induced Rhythms

Fascicular blocks are a type of conduction abnormality that occurs when the electrical impulse is blocked in one of the fascicles of the left bundle branch. The most common fascicular block-induced rhythms are:

Left anterior fascicular block (LAFB): This rhythm is characterized by a left axis deviation with a normal QRS complex.
Left posterior fascicular block (LPFB): This rhythm is characterized by a right axis deviation with a normal QRS complex.
Bifascicular block: This rhythm is characterized by a block in two of the fascicles of the left bundle branch, resulting in a wide QRS complex.

Rhythms Caused by Chamber Enlargement

Chamber enlargement occurs when one of the heart chambers becomes enlarged, causing changes in the ECG. The most common rhythms caused by chamber enlargement are:

Left ventricular hypertrophy (LVH): This rhythm is characterized by a tall, peaked QRS complex with a left axis deviation.
Right ventricular hypertrophy (RVH): This rhythm is characterized by a tall, peaked QRS complex with a right axis deviation.
Left atrial enlargement (LAE): This rhythm is characterized by a P wave greater than 40 milliseconds in duration.

Effects of Drugs and Electrolytes on the ECG

Certain medications and electrolyte imbalances can affect the ECG, making it essential to consider these factors when interpreting the results. The most common effects of drugs and electrolytes on the ECG are:

Digitalis toxicity: This occurs when the digitalis medication is too high, causing a prolongation of the QT interval and a widening of the QRS complex.
Hypokalemia: This occurs when the potassium level is too low, causing a prolongation of the QT interval and a widening of the QRS complex.
Hyperkalemia: This occurs when the potassium level is too high, causing a shortening of the QT interval and a widening of the QRS complex.

Miscellaneous Rhythms

There are several other rhythms that can be identified on an ECG, including:

Wolff-Parkinson-White (WPW) syndrome: This rhythm is characterized by a short PR interval and a wide QRS complex.
Long QT syndrome: This rhythm is characterized by a prolonged QT interval.
Brugada syndrome: This rhythm is characterized by a right bundle branch block pattern with ST elevation in leads V1-V3.

Conclusion

In conclusion, this third installment of the Electrocardiography series has provided a comprehensive review of advanced rhythms and ECG interpretation. We have discussed pacemaker-generated rhythms, rhythms associated with acute myocardial infarction, fascicular block-induced rhythms, rhythms caused by chamber enlargement, the effects of drugs and electrolytes on the ECG, and miscellaneous rhythms. By understanding these concepts, healthcare professionals can improve their ability to diagnose and manage cardiac conditions, ultimately improving patient outcomes.

References

American Heart Association (AHA). (2015). Advanced Cardiovascular Life Support (ACLS) Provider Manual.
American College of Cardiology (ACC). (2017). ACC/AHA/HRS Guideline for the Evaluation and Management of Patients with Syncope.
European Society of Cardiology (ESC). (2015). ESC Guidelines for the Management of Acute Coronary Syndromes in Patients Presenting without Persistent ST-Elevation.

Glossary

Atrial-paced rhythm: A rhythm characterized by a regular atrial rate, with a P wave preceding each QRS complex.
Ventricular-paced rhythm: A rhythm characterized by a regular ventricular rate, with a QRS complex preceding each P wave.
Atrioventricular (AV) sequential pacing: A rhythm characterized by a regular atrial and ventricular rate, with a P wave preceding each QRS complex.
ST-elevation myocardial infarction (STEMI): A rhythm characterized by a tall, peaked QRS complex with ST elevation in two or more contiguous leads.
Non-ST-elevation myocardial infarction (NSTEMI): A rhythm characterized by a normal or slightly elevated ST segment in two or more contiguous leads.
Left bundle branch block (LBBB): A rhythm characterized by a wide QRS complex with a left axis deviation.
Left anterior fascicular block (LAFB): A rhythm characterized by a left axis deviation with a normal QRS complex.
Left posterior fascicular block (LPFB): A rhythm characterized by a right axis deviation with a normal QRS complex.
Bifascicular block: A rhythm characterized by a block in two of the fascicles of the left bundle branch, resulting in a wide QRS complex.
Left ventricular hypertrophy (LVH): A rhythm characterized by a tall, peaked QRS complex with a left axis deviation.
Right ventricular hypertrophy (RVH): A rhythm characterized by a tall, peaked QRS complex with a right axis deviation.
Left atrial enlargement (LAE): A rhythm characterized by a P wave greater than 40 milliseconds in duration.
Digitalis toxicity: A condition that occurs when the digitalis medication is too high, causing a prolongation of the QT interval and a widening of the QRS complex.
Hypokalemia: A condition that occurs when the potassium level is too low, causing a prolongation of the QT interval and a widening of the QRS complex.
Hyperkalemia: A condition that occurs when the potassium level is too high, causing a shortening of the QT interval and a widening of the QRS complex.
Wolff-Parkinson-White (WPW) syndrome: A rhythm characterized by a short PR interval and a wide QRS complex.
Long QT syndrome: A rhythm characterized by a prolonged QT interval.
Brugada syndrome: A rhythm characterized by a right bundle branch block pattern with ST elevation in leads V1-V3.
Electrocardiography Part III: Advanced Rhythms and ECG Interpretation - Q&A ====================================================================

Introduction

In our previous article, we discussed advanced rhythms and ECG interpretation, including pacemaker-generated rhythms, rhythms associated with acute myocardial infarction, fascicular block-induced rhythms, rhythms caused by chamber enlargement, the effects of drugs and electrolytes on the ECG, and miscellaneous rhythms. In this Q&A article, we will answer some of the most frequently asked questions about ECG interpretation.

Q: What is the difference between a normal sinus rhythm and a paced rhythm?

A: A normal sinus rhythm is a rhythm that originates from the sinoatrial (SA) node and has a normal PR interval and QRS complex. A paced rhythm, on the other hand, is a rhythm that is generated by a pacemaker and has a different PR interval and QRS complex.

Q: How do I identify a pacemaker-generated rhythm on an ECG?

A: To identify a pacemaker-generated rhythm on an ECG, look for a regular rhythm with a different PR interval and QRS complex. The P wave may be absent or hidden in the QRS complex. The QRS complex may be wide and notched.

Q: What is the difference between a STEMI and a NSTEMI?

A: A STEMI (ST-elevation myocardial infarction) is a type of heart attack that occurs when the blood flow to the heart is blocked, causing damage to the heart muscle. A NSTEMI (non-ST-elevation myocardial infarction) is a type of heart attack that occurs when the blood flow to the heart is blocked, but the damage is not as severe.

Q: How do I identify a STEMI on an ECG?

A: To identify a STEMI on an ECG, look for a tall, peaked QRS complex with ST elevation in two or more contiguous leads.

Q: What is the difference between a LBBB and a RBBB?

A: A LBBB (left bundle branch block) is a type of conduction abnormality that occurs when the electrical impulse is blocked in the left bundle branch. A RBBB (right bundle branch block) is a type of conduction abnormality that occurs when the electrical impulse is blocked in the right bundle branch.

Q: How do I identify a LBBB on an ECG?

A: To identify a LBBB on an ECG, look for a wide QRS complex with a left axis deviation.

Q: What is the difference between a WPW syndrome and a LBBB?

A: A WPW (Wolff-Parkinson-White) syndrome is a type of arrhythmia that occurs when there is an abnormal electrical pathway in the heart. A LBBB (left bundle branch block) is a type of conduction abnormality that occurs when the electrical impulse is blocked in the left bundle branch.

Q: How do I identify a WPW syndrome on an ECG?

A: To identify a WPW syndrome on an ECG, look for a short PR interval and a wide QRS complex.

Q: What is the difference between a long QT syndrome and a Brugada syndrome?

A: A long QT syndrome is a type of arrhythmia that occurs when the QT interval is prolonged. A Brugada syndrome is a type of arrhythmia that occurs when there is an abnormality in the right bundle branch.

Q: How do I identify a long QT syndrome on an ECG?

A: To identify a long QT syndrome on an ECG, look for a prolonged QT interval.

Q: What is the difference between a hyperkalemia and a hypokalemia?

A: A hyperkalemia is a condition that occurs when the potassium level is too high. A hypokalemia is a condition that occurs when the potassium level is too low.

Q: How do I identify a hyperkalemia on an ECG?

A: To identify a hyperkalemia on an ECG, look for a shortening of the QT interval and a widening of the QRS complex.

Conclusion

In conclusion, ECG interpretation is a complex and nuanced field that requires a deep understanding of the underlying physiology and anatomy of the heart. By understanding the differences between various rhythms and arrhythmias, healthcare professionals can improve their ability to diagnose and manage cardiac conditions, ultimately improving patient outcomes.

References

American Heart Association (AHA). (2015). Advanced Cardiovascular Life Support (ACLS) Provider Manual.
American College of Cardiology (ACC). (2017). ACC/AHA/HRS Guideline for the Evaluation and Management of Patients with Syncope.
European Society of Cardiology (ESC). (2015). ESC Guidelines for the Management of Acute Coronary Syndromes in Patients Presenting without Persistent ST-Elevation.

Glossary

Normal sinus rhythm: A rhythm that originates from the sinoatrial (SA) node and has a normal PR interval and QRS complex.
Paced rhythm: A rhythm that is generated by a pacemaker and has a different PR interval and QRS complex.
ST-elevation myocardial infarction (STEMI): A type of heart attack that occurs when the blood flow to the heart is blocked, causing damage to the heart muscle.
Non-ST-elevation myocardial infarction (NSTEMI): A type of heart attack that occurs when the blood flow to the heart is blocked, but the damage is not as severe.
Left bundle branch block (LBBB): A type of conduction abnormality that occurs when the electrical impulse is blocked in the left bundle branch.
Right bundle branch block (RBBB): A type of conduction abnormality that occurs when the electrical impulse is blocked in the right bundle branch.
Wolff-Parkinson-White (WPW) syndrome: A type of arrhythmia that occurs when there is an abnormal electrical pathway in the heart.
Long QT syndrome: A type of arrhythmia that occurs when the QT interval is prolonged.
Brugada syndrome: A type of arrhythmia that occurs when there is an abnormality in the right bundle branch.
Hyperkalemia: A condition that occurs when the potassium level is too high.
Hypokalemia: A condition that occurs when the potassium level is too low.