Cardiac Pace-Makers 

Pacemaker Malfunctions, Part III

Salah Atta, MDProfessor of Cardiology,Cardiology Department

Potential Problems Identifiable on an ECG Can Generally Be Assigned to Five Categories:

• Noncapture • Undersensing• Oversensing• No output• (Pseudomalfunctions)

Pacing System Malfunction

Pacing system malfunction includes problems that might arise from any of the components of the system. The following is a description of the common PM malfunctions based on presence or absence of the pacing stimulus:

A) PM Stimuli Present + Loss of Capture

B) PM Stimuli Present + Loss of Sensing

C) PM Stimuli Absent.

D) Too much Pacing.

 

A) Pacing Stimulus Present with Loss of Capture

Noncapture or loss of capture1-Diagnosis:

Stimulus + NO subsequent paced P or QRS complex

2-Check spike

3-DD from fai lure to sense, and the spike is f ired but fal l in the physiological refractory period.

4-Consider the cause of loss of capture?

5

Noncapture/Failure to Capture

Pacer’s electrical stimulus (pacing) fails to depolarize (capture) the heart. SoPacing is simply unsuccessful at stimulating a contraction

ECG shows properly timed pacer spikes but no cardiac response

↓ CO occurs↓ Investigation: X-ray chest , PM check by 

programmer, full lab work.

Problems with PacemakersFailure to Capture

Causes: • Threshold rise.• Lead dislodgement• Lead fracture

Less Common Causes of Noncapture May Include:

• Twiddler’s syndrome• Electrolyte abnormalities e.g.

hyperkalemia• Myocardial infarction• Drug therapy• Battery depletion• Exit block

 

B) Pacing Stimulus Present whenever unexpected Undersensing

1-Diagnosis of Undersensing:

Spontaneous P or QRS complex, followed by a Stimulus (which should not have been fired)

2-Check Set Sensit ivity.

3-Consider the Cause of Undersensing?

4-Increase Sensitivity Temporari ly Til l Cause is Treated .

9

Undersensing:  Failure to sense

Pacer fails to detect an intrinsic rhythm

Paces unnecessarily (overpacing)

Patient may feel “extra beats”

If an unneeded pacer spike falls in the latter portion of T wave, dangerous tachyarrhythmias or V fib may occur (R on T).

non-sensed R-waves

Ventricular Undersensing

Causes of UndersensingDislodged Lead Insulation BreakToo low sensitivity

Problem Solving Program the sensitivity to a lower number

i.e increase the sensitivity.

 

C) Pacing Stimuli Absent

A

B

Problems with PacemakersFailure to Pace (Pauses)

Causes: • Oversensing• Battery failure• Internal insulation failure• Conductor coil fracture

Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine, 7th ed., 2005.

 

C) Pacing Stimuli Absent

1-Diagnosis: NO pacing stimuli + NO P or QRS complex

2-Consider one of three possible system malfunctions:

1-Oversensing, 2-Open Circuit, 3-Defective Battery

3-DD between the three possible system malfunctions:

Magnet->stimulus->P or QRS=Oversensing

Magnet->no stimulus, or stimulus->No P or QRS=Open Circuit

4-Consider causes and manage accordingly

Oversensing

• Definition : The sensing of events other than P or R-

waves by the pacemaker circuit e.g T wave, A spiKe, Myopotentials

Detects extraneous signals such as those produced by electrical equipment or the activity of skeletal muscles (tensing, flexing of chest muscles)

So inhibits pacing as it would a true heart beat so causing pauses or underpacing.

Causes of Oversensing

• Too high sensitivity, • Insulation Break, Intermittent Lead

Fracture.• Myopotentials. -EMI.

• Program sensitivity to a higher number (↓sensitivity).

• Change polarity to bipolar

• Program the refractory period longer

Problem Solving

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Pacer Failure

A. Earlyelectrode displacement/breakage

B. Failure > 6 monthsPremature battery depletion

Faulty pulse generator

Possible problems with DDD pacing1. Tracking of a too fast atrial rate may cause

serious ventricular response (e.g in case of atrial tachycardia, atrial flutter or atrial fibrillation) if no mode switch and high upper tracking rate.

2. Pacemaker mediated tachycardia.3. Ventricular inhibition 2ry to atrial pacing

may cause asystole (Cross talk).4. Others.

Pacemaker Pseudomalfunctions

Pacemaker Pseudomalfunctions

• Pacemaker mediated tachycardia:

Pacemaker Mediated Tachycardia (PMT)

Rapid ventricular pacing due to RETROGRADE CONDUCTION, sensed by the PM and responding by V pacing and

so on, most commonly at exactly the upper rate limit.

Retrograde Conduction• Propagation of an impulse from the ventricle back

to the atrium, Also known as VA conduction.

• 60 % of the population have the ability to conduct retrogradely

• 33 % of patients with complete heart block have the ability to conduct retrogradely

• Average retrograde conduction time= 235ms ± 55 ms

AVD

PVARP PVARP

Retrograde P waves

PVARP PVARP

PVC

Pacemaker Mediated Tachycardia

AVD

PVARP AREPVARP

AVD

PVARP

Retrograde P wavePVC

Prolong PVARP or Atrial Refractory Extension after a PVC

Pacemaker Mediated TachycardiaProblem Solving

Crosstalk• Sensing of the atrial output pulse by the ventricular sense

amplifier

• Inappropriate inhibition of the ventricular pacing due to sensing of the atrial output pulse by the ventricular sense amplifier.

• Crosstalk is only seen in dual chamber or biventricular pacemakers. Also called crosstalk inhibition, far-field sensing, or self-inhibition.

Problems with PacemakersFailure to Pace

Causes: • Crosstalk

Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine, 7th ed., 2005.

Management by programming a ventricular blanking period

Factors Affecting Crosstalk

• Atrial pulse amplitude and pulse width

• Ventricular sensitivity

• Anatomical location of atrial and ventricular electrodes

Managing Crosstalk

• Atrial Pulse Energy

• Ventricular Sensitivity

• Ventricular Blanking Period

Ventricular Blanking Period (VB)

• A short (21-75 ms) period that begins simultaneously with an atrial output pulse and during which the ventricular sense amplifier is totally blind to incoming signals but it is modifiable only by the manifacturer.

AV delay

VB

Fusion and Pseudofusion beats

PM behaviour above ULI Pacemaker Wenckebach

Mode Switchingfrom DDD to DDI or VVI

Implantable Cardioverter Defibrillator (ICD)

ICD Implantation

• Secondary prevention: Prevention of SCD in patients with prior VF or sustained VT.

• Primary prevention: Prevention of SCD in individuals without a h/o VF or sustained VT.

Indications For ICD

• VF/sustained unstable VT not in the setting of a completely reversible cause.

• LVEF ≤ 35%, CHF NYHA class II, III.• Ischemic dilated cardiomyopathy, LVEF ≤ 40%,

NSVT and inducible sustained VT.• Syncope, LV dysfunction, inducible sustained VT.• High risk patients with: hypertrophic

cardiomyopathy, LQT syndrome, RV dysplasia, Brugada syndrome

• Impedance measurementImpedance measurement : 300 - 1000 : 300 - 1000 ohms.... calculated / displayedohms.... calculated / displayed

• SVC coil , RV coil impedence: 30-100 VSVC coil , RV coil impedence: 30-100 V• Sensing threshold (localy sensed intrinsic Sensing threshold (localy sensed intrinsic

electrogram)electrogram)• Amplitude (Minimum : “P” - 2mV , “R” - 5mV)Amplitude (Minimum : “P” - 2mV , “R” - 5mV)

• Pacing thresholdPacing threshold• (Measured amplitude at 0.5 ms.)(Measured amplitude at 0.5 ms.)• Paced rate > = 20 ppm above spontaneous ratePaced rate > = 20 ppm above spontaneous rate• Decrement variable output : Threshold < 1-1.5V @ 0.5ms.Decrement variable output : Threshold < 1-1.5V @ 0.5ms.

ICD ImplantationImplantation MeasurementsMeasurements

Dual Chamber ICD

Ellenbogen K A, 2007Ellenbogen K A, 2007

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Shock

ICD interrogation revealed the following:

One shock was delivered, as above, with 9 other aborted shocks for long non-sustained VT (asymptomatic).

CRT Indications

• Age > 18 years, Sinus rhythm, EF less than 35%, NYHA class III-IV heart failure despite optimal medical treatment for at least 3 months.

• Indicator of dyssynchrony either:

Standard electrical criteria in the form of Wide QRS complex ≥130 ms, left bundle branch block (LBBB) with echo evidence of dyssynchrony in group 1 (or)

ECG of a wide QRS complex case

Before CRT implantation

LV lead position

After CRT implantation

Echo appearance before and 24 hours after CRT

FMR Before CRT implantation

24 hours after CRT implantation

Example 1

Atrial sensed, ventricular paced

Consistent with DDD or VDD pacing in VAT mode

The Alan E. Lindsay ECG Learning Center ; http://medstat.med.utah.edu/kw/ecg/

Example 2

Atrial paced

Consistent with AAI or DDD

The Alan E. Lindsay ECG Learning Center ; http://medstat.med.utah.edu/kw/ecg/

Example 3

Failure to Pace

The Alan E. Lindsay ECG Learning Center ; http://medstat.med.utah.edu/kw/ecg/

Example 4

Failure to Sense

The Alan E. Lindsay ECG Learning Center ; http://medstat.med.utah.edu/kw/ecg/

Thank you