EP 101

ICD Puzzle

Melanie T. Gura, RN, MSN, CNS, CCDS, FHRS, FAHA, AACC and 
Jason K. Smith, MD 
Pacemaker & Arrhythmia Services, Northeast Ohio Cardiovascular Specialists, Summa Cardiovascular Institute, Summa Health System
Akron, Ohio

Melanie T. Gura, RN, MSN, CNS, CCDS, FHRS, FAHA, AACC and 
Jason K. Smith, MD 
Pacemaker & Arrhythmia Services, Northeast Ohio Cardiovascular Specialists, Summa Cardiovascular Institute, Summa Health System
Akron, Ohio

Clinical History

The patient is a 73-year-old female with history of ischemic cardiomyopathy, s/p anterior wall myocardial infarction, hypertension, hyperlipidemia, heart failure with reduced ejection fraction (HFrEF), s/p PTCA/stent, and LV aneurysm. Her LVEF was 20%. Medications include spironolactone (25 mg ½ tab daily), losartan (100 mg ½ tab twice daily), furosemide (20 mg one daily), isosorbide mononitrate (20 mg extended release, one daily), metoprolol tartrate (25 mg one twice daily), clopidogrel (75 mg tab daily), pravastatin 80 mg tab at h.s., ranolaxine (1000 mg tab extended release ½ tab in AM and one tab evening), and sertraline (50 mg tab one daily).

A single-chamber ICD (TELIGEN 100, model E102, Boston Scientific) was implanted on November 17, 2010. The RV lead used was the ENDOTAK RELIANCE G (model 0184, Boston Scientific). The patient reported fatigue and a racing heart that caused shortness of breath, dizziness, chest fullness, and chest discomfort. One episode of dizziness occurred while shopping, and was so severe that she had to lie flat. It was also reported this patient had an episode of idioventricular rhythm. 

Device evaluation revealed no ventricular arrhythmias, with 0% ventricular pacing.

EGMs revealed no non-physiological signals.

The R wave was 12.5 mV. Ventricular stimulation thresholds were 1.2V/0.4 ms. An event recorder was ordered. 

What is causing this patient’s symptoms?
(A) Chronotropic incompetence
(B) Pacemaker syndrome
(C) Idioventricular rhythm 
(D) Backup mode pacing
(E) Ventricular tachycardia

Answer: (B) Pacemaker syndrome.

Pacemaker syndrome (PS) refers to adverse hemodynamic or electrophysiologic consequences associated with an electrically normal pacing system. Persistent or intermittent PS induces symptoms from minor to severe: general malaise, fatigue, cough, palpitations, dyspnea on exertion, symptomatic cannon a waves, or syncope. PS may limit a patient’s ability to achieve optimal functional status. Patients most susceptible to PS are those who have 1:1 retrograde VA conduction and those with low stroke volume induced by ventricular pacing. 

The device is programmed to VVI at 40 ppm. Why is the device pacing at rates >40 ppm?
(A) Rate smoothing
(B) Ventricular rate regulation
(C) Noise response
(D) Backup mode pacing
(E) Sensor-indicated pacing

Answer: (B) Ventricular rate regulation.

Ventricular rate regulation (VRR) is designed to reduce the V-V cycle length variability during partially conducted atrial arrhythmias by modestly increasing the ventricular pacing rate. The VRR algorithm calculates a VRR-indicated pacing interval paced on a weighted sum of the current V-V cycle length and the previous VRR-indicated pacing intervals. Paced intervals have more influence than sensed intervals — paced events cause a decrease in the VRR-indicated rate. For sensed intervals, the VRR-indicated rate may be increased; however, the influence is tempered by previous history.

When the VRR is programmed on in tracking modes, it is only active when an atrial tachycardia response (mode switch) has occurred. Once the tracking mode operation resumes at the termination of the atrial arrhythmia, VRR becomes inactive. When programmed on in single-chamber modes, VRR is continually active and updates the following on each cardiac cycle: VRR-indicated pacing rate, smoothed average.

VRR operates between the lower rate limit and the maximum pacing rate. VRR is programmable on or off under the atrial tachycardia parameter screen. With VRR programmed off, the patient experienced a resolution of symptoms.


Pacemaker syndrome, induced by ventricular pacing during sinus rhythm, was diagnosed in this patient with a single-chamber ICD. Pacemaker syndrome is an array of cardiovascular and neurologic symptoms/signs resulting from a disruption of AV synchrony due to suboptimal pacing, inappropriate programmed parameters, or upper-rate limit behavior of AV synchronous pacing.

This case illustrates that PS may occur in different pacing modalities that result in permanent or temporary disruption of AV synchrony. Resolution of PS can be achieved with VRR programmed off.


  1. Prinzen FW, et al. Basic physiology and hemodynamics of cardiac pacing. In: Ellenbogen KA, Kay GN, Lau CP, Wilkoff BL, (Eds). Clinical Cardiac Pacing, Defibrillation, and Resynchronization Therapy. Saunders: 2011:226-228.
  2. Barold S. Adverse effects of ventricular resynchronization induced by long-term right ventricular pacing. J Am Coll Cardiol. 2003;42;624-626. 
  3. Gura MT, et al. Case report: resolution of pacemaker syndrome with DVIR pacing. HeartRhythm. 2007;4(5S):S51. 
  4. Boston Scientific System Guide Teligen 100: Implantable Cardioverter High Energy Defibrillation. REF: E102, E110.