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Influence of Cardiac Pacing Mode on Left Atrial Appendage Flow Velocity: Implication to Systemic Embolism During VVI
Hiroyuki Yoshitomi1, Kazuaki Tanabe, Toshihiko Asanuma
1Ultrasound Research Laboratory, Medical Sciences 2-130, Mayo Clinic, 200 First Street SW, Rochester, MN 55905.
Insights
Switching from dual-chamber (DDD) to single-chamber (VVI) pacing significantly reduces left atrial appendage flow velocity. This decrease may increase the risk of thromboembolism in pacemaker patients.
Area of Science:
- Cardiology
- Biomedical Engineering
Background:
- Thromboembolism risk is higher with single-chamber ventricular demand (VVI) pacemakers compared to dual-chamber (DDD) pacemakers.
- Limited data exists on left atrial appendage (LAA) flow velocity in patients with pacemakers.
Purpose of the Study:
- To investigate the impact of pacing mode (DDD vs. VVI) on LAA flow velocity.
- To explore the relationship between LAA flow velocity and thromboembolic risk in pacemaker patients.
Main Methods:
- Nineteen patients with permanent DDD pacemakers underwent transesophageal echocardiography.
- LAA flow velocity was measured during both DDD pacing and VVI pacing.
- Patients were categorized into atrioventricular block (AVB) and sick sinus syndrome (SSS) groups.
Main Results:
- VVI pacing significantly decreased LAA flow velocity in both SSS (43 to 23 cm/sec) and AVB (59 to 41 cm/sec) groups compared to DDD pacing.
- In patients with retrograde ventriculoatrial conduction during VVI pacing, LAA flow velocity markedly decreased (43 to 25 cm/sec).
- In 63% of these patients, LAA flow velocity fell below 25 cm/sec.
Conclusions:
- Reduced LAA flow velocity during VVI pacing may contribute to increased thrombus formation.
- This finding suggests a potential mechanism for the elevated thromboembolic risk observed in VVI pacemaker patients.
Abstract:
Previous studies have shown that the incidence of thromboembolism is higher in patients with single-chamber ventricular demand (VVI) pacemakers than in patients with dual-chamber (DDD) pacemakers. However, data on left atrial appendage flow velocity in pacing patients are limited. To investigate the influence of the pacing mode on the left atrial appendage flow velocity, we studied 19 patients with permanent DDD pacemakers and measured the left atrial appendage flow velocity by transesophageal echocardiography at baseline (during DDD pacing) and after switching to VVI pacing. The indications for pacemaker implantation were second- and third-degree atrioventricular block (AVB group, n = 11) and sick sinus syndrome (SSS group, n = 8). Compared with the DDD pacing mode, there was a significant decrease in the left atrial appendage flow velocity during VVI pacing in both the SSS group (43 +/- 14 vs 23 +/- 7 cm/sec, P < 0.05) and the AVB group (59 +/- 18 vs 41 +/- 18 cm/sec, P < 0.05). In eight patients with persistent retrograde ventriculoatrial conduction during VVI pacing, the left atrial appendage flow velocity was markedly decreased (from 43 +/- 16 to 25 +/- 9 cm/sec, P < 0.05). In five (63%) of the eight patients, left atrial appendage flow velocity was less than 25 cm/sec. A reduction in left atrial appendage flow velocity when switching from DDD to VVI pacing may account for an increased risk of thrombus formation in the left atrial appendage (an increased thromboembolic risk in patients in sinus rhythm with VVI pacemakers).