Implantable Cardioverter Defibrillators – Improving Risk Stratification


Worldwide three million people a year die from sudden cardiac death (SCD). In most cases there is no warning and the heart is stopped by a sudden arrhythmia. We know that some people are at high risk of sudden cardiac death and can prevent their deaths with an implantable cardioverter defibrillator (ICD) that is implanted in a minor operation.

However, most people who die from sudden cardiac death are not found to be at high risk by our current risk markers and 40% of the people who have ICDs do not have therapy within the first 4 years after implant. We need new and better ways of identifying people who are at high risk of sudden cardiac death so that we can prevent their deaths with ICDs. Our understanding of the electrical signals in the heart has increased considerably in recent years; in no small part this is due to our Principal Investigator Professor Andre Ng's basic science work. This study aims to take the understanding of action potential duration (APD) restitution gained through our work and other studies in humans and in computer simulations and translate it into a fresh way of assessing risk of sudden cardiac death.

This study will carefully examine electrical activity, using APD restitution, in the hearts of patients who are having ICDs fitted because of their high risk of sudden cardiac death and combine this with a detailed heart scan, assessment of autonomic nervous system and gene expression data. We will then follow these patients up to see who benefits from their ICD. This wide ranging information will give us as complete a picture as possible of the factors that cause sudden cardiac death. We hope to use this to identify better predictors of sudden cardiac death.

The study hypotheses are as follows:


1. Regional Restitution Instability Index (R2I2) will be significantly higher in patients reaching the endpoint of ventricular endpoint / sudden cardiac death than in those not.

2. An R2I2 cut-off of 1.03 will partition patients into high and low risk groups.


3. Peri-infarct zone mass in grams will be significantly higher in patients reaching the endpoint of ventricular endpoint / sudden cardiac death than in those not.

Full Title of Study: “Improving Risk Stratification of Patients for Implantable Cardioverter Defibrillators Through Electrophysiological Tests, Cardiac Magnetic Resonance Imaging, Autonomic Function Tests, RNA Analysis and Plasma Biomarkers.”

Study Type

  • Study Type: Observational
  • Study Design
    • Time Perspective: Prospective
  • Study Primary Completion Date: November 2012

Arms, Groups and Cohorts

  • Ischaemic cardiomyopathy group
    • Patients with ischaemic cardiomyopathy attending for ICD implantation / Ventricular tachycardia stimulation testing as part of ICD risk stratification
  • Non-ischaemic cohort
    • Patients attending for ICD implantation / ventricular tachycardia stimulation test who do not have ischaemic cardiomyopathy.
  • Control group
    • Patients attending for electrophysiological study with no conditions that place them at risk of sudden cardiac death.

Clinical Trial Outcome Measures

Primary Measures

  • Regional Restitution Instability Index
    • Time Frame: 18months – 2years
    • Regional Restitution Instability Index (R2I2) is a measure of electrical instability. R2I2 is calculated as the mean of the standard deviation of the residuals from the mean gradients for each ECG lead across a range of diastolic intervals. An R2I2 cut-off of 1.03 (no units) will partition the study population into high and low risk groups.

Secondary Measures

  • Peri-infarct zone
    • Time Frame: 18months-2 years
    • Peri-infarct zone is calculated from cardiac magnetic resonance imaging scans with late gadolinium enhancement. The full width half maximum technique will be used and Peri-infarct zone assessed using peri-infarct zone mass in grams.

Participating in This Clinical Trial

Inclusion Criteria

  • Attending for ICD implantation under NICE criteria or attending for an ICD box-change procedure or attending for an Electrophysiological test as part of NICE assessment for ICD implantation
  • Age >18
  • History of ischaemic heart disease or non-ischaemic cardiomyopathy or inherited sudden cardiac death syndrome.

Exclusion Criteria

  • <28 days since acute coronary syndrome / cardiac surgery
  • Unable to give informed consent
  • Women who are pregnant / planning pregnancy
  • Contraindication for defibrillator safety margin test
  • Haemodynamic instability
  • Severe valvular heart disease
  • Symptomatic, severe, coronary artery disease
  • Recent stroke

Gender Eligibility: All

Minimum Age: 18 Years

Maximum Age: N/A

Are Healthy Volunteers Accepted: Accepts Healthy Volunteers

Investigator Details

  • Lead Sponsor
    • University Hospitals, Leicester
  • Collaborator
    • University of Leicester
  • Provider of Information About this Clinical Study
    • Sponsor
  • Overall Official(s)
    • G. Andre Ng, MBCHb, PhD, Principal Investigator, University of Leicester


Nicolson WB, McCann GP, Brown PD, Sandilands AJ, Stafford PJ, Schlindwein FS, Samani NJ, Ng GA. A novel surface electrocardiogram-based marker of ventricular arrhythmia risk in patients with ischemic cardiomyopathy. J Am Heart Assoc. 2012 Aug;1(4):e001552. doi: 10.1161/JAHA.112.001552. Epub 2012 Aug 24.

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