From the Guidelines
An M pattern QRS complex is indicative of right ventricular hypertrophy (RVH) and should prompt further evaluation for underlying conditions such as pulmonary hypertension, congenital heart disease, or chronic lung disease. The M pattern QRS complex is characterized by an RSR' pattern (or M shape) in the right precordial leads (V1-V3), which indicates delayed conduction through the right ventricle, often due to increased muscle mass 1. This finding is clinically significant as it may indicate right heart strain.
Key Characteristics of M Pattern QRS
- Initial R wave, followed by an S wave, then another R wave, creating an RSR' pattern (or M shape) in the right precordial leads (V1-V3) 1
- Delayed conduction through the right ventricle, often due to increased muscle mass
- May be associated with other RVH criteria such as right axis deviation, P pulmonale, and clinical signs of right heart failure
Diagnostic Approach
- Further assessment should include checking for other RVH criteria 1
- Additional diagnostic testing like echocardiography is typically warranted to confirm RVH and determine the underlying cause 1
Treatment
- Treatment focuses on addressing the primary condition causing the right ventricular strain rather than the ECG pattern itself 1 According to the 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay 1, the diagnosis and management of RVH should be based on a comprehensive evaluation of the patient's clinical presentation, ECG findings, and results of additional diagnostic testing.
From the FDA Drug Label
Changes in the electrocardiogram particularly in QRS axis or width, are clinically significant indicators of tricyclic antidepressant toxicity. A maximal limb-lead QRS duration of ≥0. 10 seconds may be the best indication of the severity of the overdose.
The M pattern QRS is not explicitly mentioned in the drug label. However, it does mention changes in the QRS axis or width as indicators of tricyclic antidepressant toxicity, and a maximal limb-lead QRS duration as an indication of overdose severity.
- Key points:
- Changes in QRS axis or width are indicators of toxicity
- QRS duration ≥0.10 seconds indicates severity of overdose Based on the information provided in the drug label 2, it appears that changes in the QRS complex can be an indicator of tricyclic antidepressant toxicity.
From the Research
QRS Pattern
The QRS pattern is a crucial aspect of electrocardiography (ECG) that can provide valuable information about the heart's condition.
- The QRS complex represents the ventricular depolarization, and its morphology can be affected by various factors, including myocardial ischemia, infarction, and cardiomyopathy 3, 4, 5.
- Studies have shown that abnormal QRS patterns, such as distortion of the terminal portion of the QRS, can be associated with increased infarct size and long-term prognosis in patients with acute myocardial infarction 5.
- High-frequency QRS analysis (HF-QRS) has been proposed as a novel tool to supplement ST evaluation during stress ECG, demonstrating incremental diagnostic value in identifying substantial myocardial ischemia 3.
Clinical Significance
The clinical significance of QRS patterns can vary depending on the context and underlying condition.
- In patients with cardiomyopathy, QRS scores can identify and quantify scar size, despite ECG confounders, and higher QRS-estimated scar size is associated with increased arrhythmogenesis 4.
- Abnormal stress electrocardiography with normal cardiac imaging during stress testing can be a discordant result, and its significance is uncertain, but meta-analyses suggest that it may be associated with an increased risk of major adverse cardiovascular events 6.
- In patients with acute myocarditis, an early repolarization electrocardiographic pattern can be observed, but its significance is not associated with a worse prognosis, and inflammation/swelling localized to the left ventricular epicardium may provide a mechanistic insight into this pattern 7.