QT Interval Dynamics BIBO Stability Assessment

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Solution Overview

Problem

Current methods for assessing bounded-input bounded-output (BIBO) stability in QT interval dynamics from clinical ECG recordings are unreliable due to the inability to account for short-term memory, which is essential for predicting ventricular arrhythmias.

Innovation Solution

A method using an autoregressive model with exogenous input (ARX) to model QT interval dynamics, assessing BIBO stability in the z-domain, and predicting ventricular arrhythmias by incorporating the dependence of QT interval on several prior QT intervals and RR intervals, allowing for the evaluation of stability without eliminating short-term memory.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If constant pacing protocols are used to eliminate short-term memory, then QTI restitution slope measurement becomes simpler, but the ability to predict arrhythmia in clinical settings deteriorates because clinical heart rhythms are non-constant

Engineering Contradiction:

ImproveQTI restitution slope measurementVSAvoidarrhythmia prediction accuracy

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The patent transitions from static constant pacing protocols to dynamic analysis of non-constant clinical heart rhythms. The method analyzes QTI dynamics during actual varying heart rates in clinical settings, capturing the realistic behavior of cardiac repolarization under physiological conditions rather than artificial constant pacing.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the fundamental parameter being measured from QTI restitution slope (under constant pacing) to BIBO stability of QTI dynamics (under varying heart rates). This parameter transformation allows assessment of arrhythmia risk while preserving short-term memory effects present in clinical recordings.

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If APD restitution slope is used as the measure, then the assessment of BIBO stability is simplified, but the prediction of arrhythmia fails when short-term memory cannot be eliminated by pacing protocols

Engineering Contradiction:

ImproveBIBO stability assessmentVSAvoidarrhythmia prediction

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent replaces the mechanical/APD-level restitution slope measurement with an ECG-level BIBO stability analysis. Instead of measuring action potential duration at the cellular level, the method uses readily available clinical ECG signals to assess the stability of ventricular repolarization dynamics.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces QTI dynamics as an intermediary between cellular APD dynamics and clinical arrhythmia prediction. The QTI serves as a global manifestation of ventricular repolarization that bridges the gap between microscopic cellular behavior and macroscopic clinical outcomes, allowing non-invasive assessment of BIBO stability.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Ease of manufacture

If invasive constant pacing is applied to eliminate activation history effects, then the measurement protocol becomes standardized, but the contribution of short-term memory to QTI dynamics and arrhythmia initiation cannot be evaluated

Engineering Contradiction:

Improvemeasurement protocol standardizationVSAvoidshort-term memory contribution

Core Design Contradiction:

Ease of manufactureVSLoss of information

Solution Approach 1:

The patent inverts the conventional approach by not trying to eliminate short-term memory effects but rather preserving and utilizing them. Instead of using constant pacing to remove activation history effects, the method analyzes QTI dynamics during natural varying heart rates where activation history effects are present, treating them as valuable information rather than noise.

Inventive Principle:

Principle #13The other way round (Inversion)

Data Source

PatentUS9662027B2Methodology for assessing the bounded-input bounded-output instability in QT interval dynamics: application to clinical ECG with ventricular tachycardia

Publication Date: 2017.05.30 JOHNS HOPKINS UNIVERSITY

AI summary

The present invention is directed to a method for determining onset of ventricular arrhythmias using bounded-input bounded-output stability of QT interval (QTI) dynamics. The method of the present invention includes two parts. A first part of the method determines the dependence of each QTI on several prior QTIs and RR intervals (RRI). This determination is represented as an autoregressive model with exogenous input (ARX). A second part of the method determines the BIBO stability of the ARX model in the z-domain. The metrics associated with the first and second parts of the method are then used to predict onset of arrhythmia.