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Logo of thijTexas Heart Institute JournalSee also Cardiovascular Diseases Journal in PMCSubscribeSubmissionsTHI Journal Website
Tex Heart Inst J. 2016 June; 43(3): 270–271.
Published online 2016 June 1. doi:  10.14503/THIJ-16-5846
PMCID: PMC4894713

Heart Block in a Pacemaker: Does This Mean Trouble?

We present a finding in a 61-year-old woman whose St. Jude Medical dual-chamber permanent pacemaker had been implanted to treat symptomatic bradycardia. The pacemaker, programmed in DDD mode, had a lower rate limit of 60 beats/min and an upper limit of 120 beats/min, a paced atrioventricular (AV) delay period of 250 ms, and a sensed AV delay period of 225 ms.

What happened during the first 3 complexes (Fig. 1)?

  • A) Ventricular oversensing with inappropriate inhibition of ventricular pacing.
  • B) Pacemaker-mediated AV delay attempting to allow intrinsic ventricular activity.
  • C) Failure of ventricular capture with a ventricular escape rhythm.
  • D) Pseudofusion of an attempted ventricular pacing event with a coincidental delayed ventricular complex.

Focus on EcGs: Answer #3


B) Pacemaker-mediated AV delay attempting to allow intrinsic ventricular activity.

Some St. Jude Medical devices have an optional programming mode called Ventricular Intrinsic Preference (VIP™) Technology. This incidental finding on the electrocardiogram is a normal result of a functioning program.

The MOde Selection Trial (MOST) investigators identified an increased rate of heart-failure–related hospitalizations in patients with a right ventricular (RV) pacing burden >40%.1,2 Olshansky and colleagues later investigated the effect of DDDR mode with a programmed AV delay algorithm to reduce back-up pacing.3 The AV delay algorithm decreased the RV-pacing percentage and thereby negated the increased risk of heart-failure hospitalizations.

The VIP mode operates by means of a programmed algorithm that enables a device to extend its AV delay period and monitor for intrinsic ventricular activity during a search interval. If the device senses such activity, it activates the VIP mode and temporarily extends the AV delay period for the next cycle. By extending the AV delay, intrinsic conduction is more likely and the RV pacing burden is reduced. However, if the device is required to pace despite its extended AV period, the VIP mode deactivates and the AV delay period returns to normal.

Figure 2 shows the device in VIP mode with an AV delay that has been temporarily extended by 190 ms, to 415 ms. However, it must pace at this extended AV interval for 3 consecutive beats. This signals the deactivation of VIP mode, and the device returns to its previously programmed AV delay interval of 225 ms.

This type of programming is beneficial for patients who have intermittent AV block and those who have a slightly prolonged first-degree block. It should be avoided in patients who have complete heart block, a markedly prolonged first-degree block, or indications for cardiac resynchronization therapy.

To participate in a moderated discussion of this case, go to Two weeks from the original posting date, the discussion will close, but the comments will remain online for reference.


Section Editors: Yochai Birnbaum, MD, Mohammad Saeed, MD, and James M. Wilson, MD

From: Department of Cardiology, Baylor College of Medicine, Houston, Texas 77030


1. Sweeney MO, Hellkamp AS, Ellenbogen KA, Greenspon AJ, Freedman RA, Lee KL. et al. Adverse effect of ventricular pacing on heart failure and atrial fibrillation among patients with normal baseline QRS duration in a clinical trial of pacemaker therapy for sinus node dysfunction. Circulation. 2003;107(23):2932–7. [PubMed]
2. Wilkoff BL, Cook JR, Epstein AE, Greene HL, Hallstrom AP, Hsia H. et al. Dual-chamber pacing or ventricular backup pacing in patients with an implantable defibrillator: the Dual Chamber and VVI Implantable Defibrillator (DAVID) Trial. JAMA. 2002;288(24):3115–23. [PubMed]
3. Olshansky B, Day JD, Moore S, Gering L, Rosenbaum M, McGuire M. et al. Is dual-chamber programming inferior to single-chamber programming in an implantable cardioverter-defibrillator? Results of the INTRINSIC RV (Inhibition of Unnecessary RV Pacing with AVSH in ICDs) study. Circulation. 2007;115(1):9–16. [PubMed]

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