Is your heart's electrical signal spreading correctly? This tool helps you analyze your QRS duration from an ECG. It's a simple way to check how efficiently your heart's ventricles are being activated.
The QRS Complex Interpreter measures the time from the beginning of ventricular depolarization to its completion. An abnormal QRS duration can indicate conduction problems in your heart.
Your heart's electrical signal spreads through the ventricles via the bundle branches. The QRS complex measures this time—when it's too wide, it may signal a block or abnormal pathway.
The QRS complex represents ventricular depolarization — the electrical activation of the heart's main pumping chambers. It starts when the electrical signal enters the ventricles via the bundle branches and ends when both ventricles are fully activated. The distinctive spike shape reflects the large muscle mass of the ventricles generating a strong electrical signal.
Not always. The significance depends on the cause:
• RBBB in isolation: Often benign, especially in younger people
• LBBB: More often associated with underlying heart disease
• New wide QRS: Should always be evaluated promptly
• Wide QRS with symptoms: Requires immediate attention
Context matters — a wide QRS during a rapid heart rate is more concerning than at rest.
Bundle branch block occurs when one of the heart's electrical "highways" (the right or left bundle branch) is damaged or blocked. When this happens, the electrical signal must travel through the heart muscle directly instead of the fast conduction system, which takes longer and widens the QRS. Right bundle branch block (RBBB) affects the right ventricle; left bundle branch block (LBBB) affects the left ventricle.
Both cause wide QRS complexes (≥120ms) but with different patterns:
• RBBB: RSR' pattern in V1 (like rabbit ears), wide S wave in V6. Often benign, can be a normal variant.
• LBBB: Broad, notched R wave in lateral leads (V5, V6), deep S wave in V1.
More often indicates underlying heart disease.LBBB generally requires more thorough cardiac evaluation than RBBB.
Yes, several medications can widen the QRS by slowing cardiac conduction:
• Class I antiarrhythmics: Flecainide, procainamide, quinidine
• Tricyclic antidepressants: Amitriptyline, nortriptyline (especially in overdose)
• Some antipsychotics: Thioridazine
• Local anesthetics: Lidocaine toxicity
Drug-induced QRS widening is usually dose-dependent and reversible.
High potassium levels in the blood affect how cardiac cells conduct electrical signals. As potassium rises, it progressively slows conduction velocity throughout the heart. The ECG changes typically progress from peaked T waves → PR prolongation → QRS widening → sine wave pattern → cardiac arrest. QRS widening from hyperkalemia is a medical emergency requiring immediate treatment.
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