Prospective Randomized Evaluation of the WATCHMAN LAA Closure Device in Patients With Atrial Fibrillation Versus Long Term Warfarin Therapy


The PREVAIL trial was designed to confirm the results of the PROTECT AF trial and validate the safety of the implant procedure, including a minimum of 20% of randomised patients will be enrolled at institutions that did not participate in a previous WATCHMAN study (PROTECT AF or CAP Registry) and a minimum of 25% of randomised patients enrolled by new operators at any institution.

A total of 407 patients were randomised 2:1 device vs. warfarin control in the PREVAIL trial

Patients enrolled in PREVAIL must have been Warfarin eligible and have a CHADS2 score of ≥2

The PREVAIL co-primary endpoints were as follows:

  • 1st co-primary endpoint: Acute (7-day) occurrence of death, ischemic stroke, systemic embolism and procedure or device related complications requiring major cardiovascular or endovascular intervention
  • 2nd co-primary endpoint: Comparison of composite of stroke, systemic embolism, and cardiovascular/unexplained death at 18 months follow-up
  • 3rd co-primary endpoint: Comparison of ischemic stroke or systemic embolism occurring from greater than 7 days post randomization to 18 months follow-up



PREVAIL trial-enrolled patients with higher risk of stroke as determined by CHADS2 scoring system

  • PREVAIL CHADS2 score was 2.6 versus 2.2 in PROTECT AF
  • Average age of the patient in PREVAIL was 74 years compared to 71 years in PROTECT AF
  • 33.8% of patients had diabetes in PREVAIL vs.24.4% in PROTECT AF.
  • 27.5% of patients had prior stroke compared to 17.7% in PROTECT AF.


PREVAIL Demographics Chart



1st co-primary endpoint: The PREVAIL trial MET the pre-specified criteria for the 1st co-primary endpoint (procedural related safety <7days)

  • The observed adverse event rate was 2.2%, resulting in an observed upper bound of 2.618% which is less than the pre-specified criterion of 2.67% (95% CI).

2nd co-primary endpoint: The PREVAIL trial DID NOT MEET the pre-specified criteria for the 2nd co-primary endpoint (efficacy of all stroke, cardiovascular death and systemic embolism at 18 months).

  • The observed adverse event rate at 18 months for BOTH Watchman and the control was 0.064, resulting in a rate ratio of 1.07, device versus control. The observed upper bound of the rate ratio was 1.88, slightly greater than the pre-specified criterion of 1.75 (95% CI)
  • The 1.07 rate ratio indicates Watchman performed similarly to warfarin with respect to this endpoint.
  • It is important to note that long term data on this endpoint is very limited. At the time of this analysis only 58 Watchman patients and 30 Control patients had passed the 18 month endpoint. All patients will undergo long-term follow up (5 years) and we will continue to update the analysis over time.
  • The PREVAIL treatment group performed similarly to prior Watchman studies, however the observed rate of stroke (0.7%) in the PREVAIL Control group was lower than in recent published warfarin studies (1.6-2.2%):


PREVAIL Trial Results


3rd co-primary endpoint: The PREVAIL trial also MET its pre-specified endpoint for the 3rd co-primary endpoint occurrence of late ischemic stroke and systemic embolism ( > 7 days post randomization) at 18 months.

  • The observed adverse event rate was 0.0253 per 100 patient years, resulting in an observed difference between the device and control group of 0.0051 per 100 patient years. The observed upper bound of 0.0268 was less than the pre-specified criterion of 0.0275 (95% CI)


Additional safety analysis of PREVAIL shows:

  • A significant increase in implant success rate (95.1%) compared to PROTECT AF (90.9%). Additionally, new implanter success rate was 93.2% and experienced implanter success rate was 96.3% (p=.282).


Successful Implants Chart


  • Seven-day serious procedure/device related vascular complications occurred in 4.4% of subjects in PREVAIL vs. 8.7% of subjects in PROTECT AF, a 49% reduction
  • Pericardial effusions requiring intervention occurred at rate of 1.9% in PREVAIL vs. 4.0% of patients in PROTECT AF, a 52% reduction and at rate comparable to other left atrial procedures.
  • New operators had only one occurrence (1.0%) of pericardial effusion requiring intervention and did not have any device embolizations, periprocedural strokes or cardiac perforations



  • Positive results from the PREVAIL trail demonstrated acute procedure and device-related safety events remained low for the WATCHMAN LAAC device.
  • The PREVAIL trial provided evidence that the Watchman device can be successfully implanted by new operators. Results showed low complication rates with both new and experienced operators and significantly lowered complications than the early stage of the PROTECT AF trial.
  • WATCHMAN is the only device-based alternative to anticoagulation that has undergone rigorous scientific study. Results of the PREVAIL trial added to the wealth of previously published data which confirmed the utility of WATCHMAN as an option for the reduction of stroke in high risk patients.


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1 Ischemic stroke rate from Holmes et al. Lancet 2009; 374:534-42
2 Connolly et al. N Engl J Med 2009; 361:1139-51
3 Granger et al. N Engl J Med 2011; 365:981-92
4 Patel et al. N Engl J Med 2011; 365:883-91

CAUTION: the law restricts these devices to sale by or on the order of a physician. Indications, contraindications, warnings and instructions for use can be found in the product labeling supplied with each device. Information for the use only in countries with applicable health authority product registrations.

SH-146302-AA MAR2013

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