Shock reducing strategies in devices



Raja Selvaraj, JIPMER

ICDs designed to treat VF


Multiple functions of ICD

  • Bradycardia pacing
  • Anti-tachycardia pacing
  • Cardioversion
  • Defibrillation

Shocks prevalence

  • A third of patients after 5 years
  • About a fifth are inappropriate

"Shock paradox"

  • Shocks worsen quality of life
  • Myocardial damage occurs with shocks
  • Shocks increase mortality

Increased mortality


Sweeney MO, Sherfesee L, DeGroot PJ, Wathen MS, Wilkoff BL. Differences in effects of electrical therapy type for ventricular arrhythmias on mortality in implantable cardioverter-defibrillator patients. Heart Rhythm. 2010 Mar;7(3):353-60. doi: 10.1016/j.hrthm.2009.11.027. Epub 2009 Dec 2. PMID: 20185109.

Not all shocks save lives


Ellenbogen KA … , Kadish A; Defibrillators in Non-Ischemic Cardiomyopathy Treatment Evaluation (DEFINITE) Investigators. Are implantable cardioverter defibrillator shocks a surrogate for sudden cardiac death in patients with nonischemic cardiomyopathy? Circulation. 2006 Feb 14;113(6):776-82.


  • Inappropriate shocks
  • Unnecessary, appropriate shocks
  • Necessary appropriate shocks

Strategies to reduce shocks

  • Control of ventricular arrhythmias
    • Drugs
    • Ablation
  • Choosing the right device ?
  • Device programming

Control of arrhythmias

ICD is not a treatment for VT

  • Not for VT storm
  • Not in presence of recurrent VT

Medical management

  • Control VA before implant
  • Heart failure treatment, AAD, beta blockers after implant
  • Sotalol useful to reduce shocks (1)
  • Amiodarone - Better than beta blocker alone or Sotalol - OPTIC trial (2)
  1. Pacifico A et al. Prevention of implantable-defibrillator shocks by treatment with sotalol. d,l-Sotalol Implantable Cardioverter-Defibrillator Study Group. N Engl J Med. 1999;340:1855–62. doi: 10.1056/NEJM199906173402402.
  2. Connolly SJ et al. Comparison of beta-blockers, amiodarone plus beta-blockers, or sotalol for prevention of shocks from implantable cardioverter defibrillators: the OPTIC Study: a randomized trial. JAMA. 2006;295:165–71. doi: 10.1056/NEJM199906173402402.


  • SMASH-VT (1)
    • 128 pts with secondary prevention ICD randomised to ablation vs no additional therapy (1)
    • 24 months - less shocks (12% vs 31%)
  • VTACH (2)
    • ICM with VT - icd alone or icd with ablation (2)
    • more freedom from VT with ablation
  1. Reddy VY et al. Prophylactic catheter ablation for the prevention of defibrillator therapy. N Engl J Med. 2007;357:2657–65. doi: 10.1056/NEJMoa065457.
  2. Kuck KH et al. Catheter ablation of stable ventricular tachycardia before defibrillator implantation in patients with coronary heart disease (VTACH): a multicentre randomised controlled trial. Lancet. 2010;375:31–40. doi: 10.1016/S0140-6736(09)61755-4.

Choosing a device. Will a dual chamber device reduce shocks ?

Dual chamber may have better detection


Friedman et al. Dual-Chamber Versus Single-Chamber Detection Enhancements for Implantable Defibrillator Rhythm Diagnosis. The Detect Supraventricular Tachycardia Study. Circulation. 2006;113:2871–2879.

Difference is small in real world

  • Atrial sensing problems may contribute to inappropriate detection in dual chamber devices
  • Improved algorithms with single chamber devices
  • Reduction in inappropriate shocks is only for slower rhythms
  • Better understanding of device programming - less inappropriate therapies

Gilliam FR et al. Real world evaluation of dual-zone ICD and CRT-D programming compared to single-zone programming: the ALTITUDE REDUCES study. J Cardiovasc Electrophysiol. 2011;22:1023–9. doi: 10.1111/j.1540-8167.2011.02086.x.

DATAS trial

  • 334 patients
  • Randomised to SC-ICD, DC-ICD or simulated SC-ICD (DC programmed as SC)
  • Lower rate of significant clinical events with DC-ICD
  • But none of primary endpoints different (not enough statistical power)

Almendral J et al. Dual-chamber defibrillators reduce clinically significant adverse events compared with single-chamber devices: results from the DATAS (Dual chamber and Atrial Tachyarrhythmias Adverse events Study) trial. Europace. 2008;10:528–35. doi: 10.1093/europace/eun072.


  • RCT of 100 patients
  • DC-ICD did not reduce inappropriate shocks

Friedman PA et al. A prospective randomized trial of single- or dual-chamber implantable cardioverter-defibrillators to minimize inappropriate shock risk in primary sudden cardiac death prevention. Europace. 2014;16:1460–8. doi: 10.1093/europace/euu022.


Focused update 2019


Stiles MK, Fauchier L, Morillo CA, Wilkoff BL; ESC Scientific Document Group. 2019 HRS/EHRA/APHRS/LAHRS focused update to 2015 expert consensus statement on optimal implantable cardioverter-defibrillator programming and testing. Europace. 2019 Sep 1;21(9):1442-1443. doi: 10.1093/europace/euz065. PMID: 31090914.

Brady programming


VF detection



  • FVT 188-250 bpm
  • Randomised to ATP or shock
  • ICM and NICM, primary and secondary prevention
  • 72% of VT in this zone could be terminated with ATP
  • Improved quality of life with ATP

Wathen MS et al. Prospective randomized multicenter trial of empirical antitachycardia pacing versus shocks for spontaneous rapid ventricular tachycardia in patients with implantable cardioverter-defibrillators: Pacing Fast Ventricular Tachycardia Reduces Shock Therapies (PainFREE Rx II) trial results. Circulation. 2004;110:2591–6. doi: 10.1161/01.CIR.0000145610.64014.E4.

VT detection



  • 1500 patients - 3 arms
  • standard programming / VT > 200 / 60 sec delay > 170, 12 sec > 200
  • First inappropriate therapy

Moss AJ et al. Reduction in inappropriate therapy and mortality through ICD programming. N Engl J Med. 2012;367:2275–83. doi: 10.1056/NEJMoa1211107.



ATP for "VF"


Personal experience


Shocks for VF


ATP for VT



  • ATP for FVT (182-250 bpm) in primary prevention ICDs
  • Cohort of 700 patients
  • Historic controls (EMPIRIC and MIRACLE-ICD)
  • First shock in 12 mths reduced from 17% to 9%

Wilkoff BL et al. Strategic programming of detection and therapy parameters in implantable cardioverter-defibrillators reduces shocks in primary prevention patients: results from the PREPARE (Primary Prevention Parameters Evaluation) study. J Am Coll Cardiol. 2008;52:541–50. doi: 10.1016/j.jacc.2008.05.011.


  • 206 pts randomised to ramp or burst for fast VT
  • Better success with burst (75% vs 56%)

Gulizia MM et al. A randomized study to compare ramp versus burst antitachycardia pacing therapies to treat fast ventricular tachyarrhythmias in patients with implantable cardioverter defibrillators: the PITAGORA ICD trial. Circ Arrhythm Electrophysiol. 2009;2:146–53. doi: 10.1161/CIRCEP.108.804211.



SVT time out


Noise rejection / Lead integrity alerts



  • ICD is not a treatment for VT
  • Dual chamber ICD does not appear justified for better discrimination
  • Ensure good R wave and small T wave
  • Program high VF rate - 250 bpm
  • Long detection interval for VT
  • ATP - during charging for VF, more than one attempt for VTs