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Electrocardiogram

Electrocardiogram

An electrocardiogram (ECG or EKG) is a critical diagnostic tool that records the electrical signals produced by the heart during each heartbeat. This recording is achieved through electrodes placed strategically on the arms, legs, and chest. The electrocardiograph amplifies these signals and produces 12 distinct tracings, offering a comprehensive understanding of the heart's electrical activity.
Three major waveforms are present in a typical ECG recording: the P wave, the QRS complex, and the T...

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Related Experiment Video

Updated: Jul 7, 2026

Benefits of Cardiac Resynchronization Therapy in an Asynchronous Heart Failure Model Induced by Left Bundle Branch Ablation and Rapid Pacing

Benefits of Cardiac Resynchronization Therapy in an Asynchronous Heart Failure Model Induced by Left Bundle Branch Ablation and Rapid Pacing

Published on: December 11, 2017

Normalized QRS Duration by LV Dimension: Eliminating Sex-Specific Differences and Predicting Cardiac

Enrui Zhang¹, Jiaxin Zeng¹, Fengwei Zou²

¹Department of Cardiology, First Affiliated Hospital, Nanjing Medical University, Nanjing, China.

JACC. Clinical Electrophysiology

|February 27, 2026

Summary

Normalized QRS duration (QRSd/LVEDD) eliminates sex differences in cardiac resynchronization therapy (CRT) efficacy. This ratio, reflecting cardiac size, better predicts outcomes than QRSd alone, guiding personalized CRT implantation.

Keywords:

QRSd/LVEDD cardiac resynchronization therapy heart failure sex-specific difference

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Last Updated: Jul 7, 2026

Benefits of Cardiac Resynchronization Therapy in an Asynchronous Heart Failure Model Induced by Left Bundle Branch Ablation and Rapid Pacing

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Published on: December 11, 2017

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Published on: April 11, 2025

Area of Science:

Cardiology
Medical Devices
Biomedical Engineering

Background:

Cardiac resynchronization therapy (CRT) efficacy shows sex-specific variations.
Relying solely on sex for CRT outcome prediction is insufficient without a cardiac rationale.

Purpose of the Study:

To assess if QRS duration normalized to cardiac size (QRSd/LVEDD) explains sex-specific CRT efficacy differences.
To determine if QRSd/LVEDD can guide CRT implantation decisions.

Main Methods:

Multicenter retrospective study of 602 heart failure patients undergoing CRT.
Primary composite outcome: all-cause mortality, heart failure hospitalizations, ventricular tachyarrhythmic events.
Used interaction analysis and structural equation modeling to evaluate QRSd/LVEDD's predictive ability and sex-specific effects.

Main Results:

Female patients had a higher QRSd/LVEDD ratio (2.66 vs 2.48).
QRSd/LVEDD adjustment eliminated observed sex differences in left ventricular ejection fraction improvement and clinical outcomes.
QRSd/LVEDD outperformed QRSd in predicting outcomes and stratified prognosis within sexes.

Conclusions:

QRSd/LVEDD effectively removes sex-specific disparities in CRT efficacy.
Sex influences CRT outcomes indirectly via QRSd/LVEDD, not directly.
QRSd/LVEDD is a superior predictor of clinical outcomes compared to QRSd for personalized CRT.