From the Guidelines
The presence of an RS interval longer than 100 ms in any precordial lead is highly suggestive of monomorphic ventricular tachycardia (VT). This feature, as outlined in the acc/aha/esc guidelines for the management of patients with supraventricular arrhythmias 1, is a key differentiator between VT and supraventricular tachycardia (SVT).
Key Features of Monomorphic VT
- An RS interval longer than 100 ms in any precordial lead
- A QRS pattern with negative concordance in the precordial leads, which is diagnostic for VT
- The presence of ventricular fusion beats, indicating a ventricular origin of the tachycardia
- QR complexes, which may indicate a myocardial scar and are present in approximately 40% of patients with VTs after myocardial infarction
Importance of ECG Interpretation
The width and morphological criteria of the QRS complex are crucial in diagnosing monomorphic VT, especially in patients with a history of myocardial infarction 1. A positive answer to inquiries about previous myocardial infarct and the first occurrence of a wide QRS-complex tachycardia after an infarct strongly indicates a diagnosis of VT.
Clinical Application
In clinical practice, it is essential to consider these ECG features when evaluating a patient with a wide QRS-complex tachycardia, as accurate diagnosis is critical for proper management and treatment, which may include antiarrhythmic medications or electrical cardioversion depending on hemodynamic stability 1.
From the Research
ECG Features of Monomorphic Ventricular Tachycardia
The following ECG features are suggestive of monomorphic ventricular tachycardia (VT):
- Negative precordial concordance: This is a key feature that distinguishes VT from other types of tachycardia 2
- Notched S wave in lead V1: Although not exclusively indicative of VT, a notched S wave in lead V1 can be seen in VT, especially when combined with other criteria
- QRS width > 140 ms: A wider QRS complex is more suggestive of VT, especially when combined with other ECG features 2
- Monophasic or biphasic QRS complexes in V1: These patterns can be seen in VT, particularly when the QRS axis is superiorly directed 2
- Deep S wave in V6: A deep S wave in lead V6 can be indicative of VT, especially when combined with other ECG features 2
Axis and QRS Morphology
The QRS axis and morphology can also provide clues to the diagnosis of VT:
- Superiorly directed QRS axis: This can be seen in VT, especially when combined with other ECG features 2
- Northwest axis: Although not exclusively indicative of VT, a northwest axis can be seen in some cases of VT
Limitations and Considerations
It is essential to consider the clinical context and combine multiple ECG features to increase the specificity of the diagnosis 2. The presence of underlying structural heart disease, such as a history of myocardial infarction, can also increase the likelihood of VT 2, 3.