Related Experiment Video
Updated: May 3, 2026
Real-Time Cardiac Mapping with a Noninvasive Imageless Electrocardiographic Imaging System
Published on: April 11, 2025
Baseline QRS axis distinguishes para-Hisian PVC from outflow tract PVCs
Masafumi Sugawara1, Jakub Sroubek1, Justin Lee1
1Cardiac Electrophysiology and Pacing Section, Department of Cardiovascular Medicine, Cleveland Clinic, Cleveland, Ohio.
Background:
Para-Hisian premature ventricular contraction (PVC) is challenging and needs to be distinguished preprocedurally from other outflow tract PVCs (OT-PVCs) based on electrocardiographic morphology.
Objective:
This study aimed to investigate whether para-Hisian PVCs can be distinguished from the right (RVOT) and left ventricular outflow tract (LVOT) by comparing the QRS axis of PVC and sinus rhythm (SR).
Methods:
We retrospectively analyzed 160 idiopathic PVC cases without conduction abnormalities. The site of origin was defined by the successful ablation site. Baseline SR and PVC axes were calculated using the net QRS amplitudes in leads I and III. Differences between SR and PVC axes were compared among para-Hisian, RVOT, and LVOT PVCs.
Results:
Seventeen para-Hisian, 84 RVOT, and 59 LVOT PVCs were identified. The mean differences between SR and PVC axes were -4.9° ± 26.1°, 42.1° ± 21.0°, and 61.2° ± 22.9°, with para-Hisian PVCs showing the smallest deviation from baseline SR axis. An axis difference of ≤18° strongly supports a para-Hisian PVC, rather than other OT-PVCs (area under the curve 0.94; sensitivity 0.94; specificity 0.82). As the SR axis deviated leftward, the positive component in lead I became more prominent in RVOT or LVOT PVCs, resulting in some cases exhibiting QRS morphologies mimicking para-Hisian PVCs (n = 14 of 84 and n = 4 of 59, respectively). However, these PVCs exhibited a substantial difference between SR and PVC axes. In contrast, para-Hisian PVCs consistently showed similarity between SR and PVC axes, regardless of baseline axis deviation.
Conclusion:
The axis of idiopathic OT-PVC can be influenced by baseline SR axis deviation. Comparison of SR and PVC axes is essential to distinguish true para-Hisian PVCs from other OT-PVCs.
Related Concept Videos
01:18Dysrhythmias IV: Characteristics of Bradyarrhythmias
01:25ECG Interpretation of Arrhythmias II: Atrial, Junctional and Ventricular Arrhythmias
01:28Electrocardiogram Fundamentals
An electrocardiogram (ECG) is a diagnostic tool for identifying cardiac conditions such as arrhythmias, conduction abnormalities, and myocardial ischemia.
Definition
An electrocardiogram (ECG) visualizes the heart's electrical activity by tracing the electrical movement associated with each heartbeat on a graph or monitor. As the heart beats, an electrical wave passes through it, correlating with the cardiac cycle events.
Parts of an ECG
An ECG utilizes electrodes on the skin...
01:29Dysrhythmias III: Characteristics of Dysrhythmias
01:16ECG Interpretation of Arrhythmias I: Sinus Arrhythmias
Types of Arrhythmias
Sinus Node Arrhythmias
Sinus Bradycardia: Originating from the sinoatrial (SA) node, sinus bradycardia involves slower impulses, resulting in a heart rate of less than 60 beats per minute (bpm). Causes include sleep, vagal stimulation, beta-blockers, hypothyroidism,...
01:25Correlation between ECG and Cardiac Cycle
A cardiac action potential originates in the SA node and spreads throughout the atria and the AV node in approximately 0.03 seconds. This results in the P wave in an ECG and triggers atrial contraction. The action potential is then briefly slowed at the AV node, allowing the atria to contract and fill the ventricles with blood before...