title: Relationship between exercise-induced heart rate increase and the formation of microbubbles and high-intensity transient signals in mechanical heart valve implanted patients.
abstract: BACKGROUND
  The formation and collapse of vapor-filled bubbles near a mechanical heart valve is called cavitation. Microbubbles can be detected in vivo by doppler ultrasonography (USG) as HITS (high intensity transient signals) in cranial circulation. We investigated the relationship between exercise induced heart rate increase and HITS formation in cranial circulation.
  
  
  METHODS
  Thirty-nine mechanical heart valve implanted (8 aortic valve replacement (AVR) + mitral valve replacement (MVR), 9 AVR, 22 MVR) patients aged 18-80 years old were included in our study. Microbubbles were counted in the left ventricular cavity via transthoracic echocardiography at rest per cardiac cycle. Afterwards transcranial Doppler USG was performed and HITS were counted in each patient's middle cerebral artery at 5 min duration. Subsequently an exercise test according to the Bruce protocol was performed. After achieving maximal heart rate, microbubbles in the left ventricle and HITS were counted again.
  
  
  RESULTS
  Microbubbles in the left ventricle and transcranial HITS increased after exercise significantly compared to resting values (15.79 ±10.91 microbubbles/beat vs. 26.51 ±18.00 microbubbles/beat, p < 0.001; 6.13 ±8.07 HITS/5 min vs. 13.15 ±15.87 HITS/5 min, p = 0.001). There was a significant correlation between microbubbles and HITS counts after peak exercise (r = 0.55, p < 0.001).
  
  
  CONCLUSIONS
  In our study, we found that the microbubbles were increasing as the heart rate increased and more HITS were propelled to the cerebral circulation. As previously shown, HITS can alter cognitive functions. Therefore heart rate control is essential in mechanical heart valve patients to protect neurocognitive functions.
authors.affiliation: Department of Cardiology, Medicana Camlica Hospitals, İstanbul, Turkey.
authors.forename: Ayşegül
authors.initials: A
authors.lastname: Sünbül
authors.affiliation: Department of Cardiovascular Surgery, Medicana Camlica Hospitals, İstanbul, Turkey.
authors.forename: Ahmet
authors.initials: A
authors.lastname: Kırbaş
authors.affiliation: Department of Anesthesiology and Reanimation, Medicana Camlica Hospital, İstanbul, Turkey.
authors.forename: Nursen
authors.initials: N
authors.lastname: Tanrıkulu
authors.affiliation: Department of Cardiology, Gaziosmanpa a Hospital, İstanbul, Turkey.
authors.forename: Cihan
authors.initials: C
authors.lastname: Sengül
authors.affiliation: Department of Cardiology, Medical Park Hospital, İstanbul, Turkey.
authors.forename: Bahadır
authors.initials: B
authors.lastname: Dağdeviren
authors.affiliation: Department of Cardiovascular Surgery, Medicana Camlica Hospitals, İstanbul, Turkey.
authors.forename: Omer
authors.initials: O
authors.lastname: Işık
keywords: exercise; high-intensity transient signals; mechanical heart valve; microbubble; transcranial