Dual Chamber Pacemaker Showing Only Ventricular Pacing: Diagnostic Approach
When a dual-chamber pacemaker displays only ventricular pacing, immediately interrogate the device to determine if this represents appropriate VDD/DDD mode function with intact atrial sensing but no atrial pacing requirement, versus a malfunction requiring intervention. 1
Initial Assessment Algorithm
Check the programmed pacing mode first - the device may be functioning correctly in VDD mode, which is designed to sense atrial activity and pace only the ventricle when AV conduction is impaired 1. In VDD mode, you will see ventricular pacing spikes without atrial pacing spikes because the system detects native atrial activity and triggers ventricular pacing after the programmed AV interval 1.
Distinguish Normal Function from Malfunction
If the patient has normal sinus node function with complete or high-grade AV block, seeing only ventricular pacing is expected and appropriate 1. The VDD mode maintains AV synchrony by sensing the patient's own P waves and pacing the ventricle accordingly 1.
If the device is programmed to DDD mode but showing only ventricular pacing, this indicates a problem - either atrial lead failure, atrial undersensing, or loss of atrial capture 2.
Device Interrogation Steps
1. Verify Pacing Mode and Parameters
- Confirm whether the device is programmed to DDD, VDD, or has been mode-switched 1
- Check if the lower rate limit is set appropriately - if the patient's intrinsic atrial rate exceeds this, atrial pacing may not be needed 3
- Review AV delay settings to ensure proper timing between atrial sensing and ventricular pacing 2
2. Assess Atrial Lead Function
Apply a magnet over the generator to force asynchronous pacing at the programmed magnet rate 2. This overrides sensing functions and forces continuous pacing in both chambers 2.
- Observe for atrial capture: Each atrial pacing spike should produce a visible P wave with appropriate morphology 2
- Check atrial sensing: Remove the magnet and reduce the pacing rate below the patient's intrinsic rate to verify that native P waves appropriately inhibit atrial pacing output 2
- Review telemetry data: Check atrial lead impedance, sensing amplitude, and pacing thresholds 2
3. Evaluate for Atrial Arrhythmias
Persistent or paroxysmal atrial fibrillation will cause the device to function as VVI/VVIR, showing only ventricular pacing 4. The ACC/AHA guidelines specify that in patients with permanent or persistent AF where rhythm control is not planned, atrial lead implantation should not be performed 4.
Common Clinical Scenarios
Scenario 1: VDD Mode with Intact Sinus Function
- This is normal operation - the device senses atrial activity and paces only the ventricle 1
- No intervention needed if the patient is asymptomatic 3
- Verify adequate atrial sensing amplitude (typically >2 mV) 2
Scenario 2: Atrial Lead Dislodgement or Failure
Atrial lead complications are the most common issue with dual-chamber systems, occurring in approximately 4-8% of cases 4. Half require surgical correction for lead repositioning 4.
- Loss of atrial capture despite adequate output suggests lead dislodgement 2
- Elevated lead impedance (>1500 ohms) or very low impedance (<200 ohms) indicates lead fracture or insulation breach 2
- Chest X-ray can confirm lead position 2
Scenario 3: Atrial Undersensing
- The device fails to detect native atrial activity, resulting in inappropriate ventricular-only pacing 2
- Reduce atrial sensitivity threshold (lower mV value = more sensitive) to improve sensing 2
- If undersensing persists despite programming changes, consider lead revision 2
Scenario 4: Development of Atrial Fibrillation
When patients develop persistent AF, the dual-chamber device effectively functions as a single-chamber ventricular pacemaker 4. The 2018 ACC/AHA/HRS guidelines recommend against maintaining an atrial lead in patients with permanent AF when rhythm control is not planned 4.
Critical Pitfalls to Avoid
Do not assume malfunction without device interrogation - many cases of "only ventricular pacing" represent appropriate device function in VDD mode or appropriate mode-switching during atrial arrhythmias 1.
Assess for pacemaker syndrome - even with appropriate ventricular pacing, loss of AV synchrony can cause symptoms including lightheadedness, syncope, or palpitations 4, 3. The ACC/AHA guidelines recommend upgrading to dual-chamber pacing if pacemaker syndrome develops 4.
Check for retrograde VA conduction - this can cause valvular regurgitation and atrial electrophysiological changes 1. Obtain a 12-lead ECG during symptoms to evaluate for retrograde P waves 3.
Verify battery status and overall system integrity - selective ventricular lead dysfunction can occur after DC cardioversion, with preferential shunting of electrical energy into the ventricular lead 5, 6. Always reassess pacing thresholds after cardioversion 5.
Management Based on Findings
If atrial lead failure is confirmed: The 2012 HRS/ACCF consensus statement notes that upgrading from single-chamber to dual-chamber pacing has a 45% complication rate and takes longer than initial implantation 4. However, for symptomatic patients with pacemaker syndrome, revision to restore dual-chamber function is recommended 4.
If the patient has developed permanent AF: Consider reprogramming to VVI/VVIR mode rather than maintaining non-functional atrial pacing 4. The guidelines explicitly state that atrial lead implantation should not be performed in patients with permanent AF when rhythm control is not planned 4.
If VDD mode is functioning appropriately: No intervention is required 1. Continue regular follow-up to monitor atrial sensing adequacy and ensure the patient remains asymptomatic 1.