Development of Left Atrial Thrombus After Coadministration of Dabigatran Etexilate and Phenytoin.

Dabigatran etexilate is a substrate of the P-glycoprotein (adenosine triphosphate-binding cassette subfamily B member 1) transport system and is subject to interactions with medications that induce or inhibit this system. The clinical relevance of the interaction between dabigatran and phenytoin has not been well described. We report a case of left atrial thrombus in a patient receiving concomitant dabigatran etexilate and phenytoin, which is a P-glycoprotein inducer. This case illustrates the potential clinical significance of the interactions of medications that affect P-glycoprotein and dabigatran.

Phase I and Phase II oxygen uptake kinetics during atrioventricular dyssynchrony in chronotropically competent pacemaker patients.

OBJECTIVE: To elucidate the effects of atrioventricular (AV) dyssynchrony on phase I and phase II oxygen uptake (V(O2)) kinetics in chronotropically competent pacemaker patients during exercise of an intensity comparable to activities of daily living. DESIGN: Blinded patients completed sub-ventilatory threshold (VT) work rate (WR) cycle ergometry exercise in random order during asynchronous AV pacing (AV OFF) and synchronous AV pacing. SETTING: Tertiary care hospital in a major city. SUBJECTS: Six chronotropically competent male pacemaker patients (mean [+/- SD] age, 68 +/- 10 years) with high-degree AV block and varying cardiac histories. RESULTS: The phase I and phase II V(O2) amplitude response and gain (deltaV(O2)/WR ratio) were lower (p < 0.05) and the time course of phase II was slower (p < 0.05) during AV OFF; however, the O2 deficit was similar (p > 0.05) across pacing modes. The stroke volume index (SVI) was consistently lower (p < 0.05) during AV OFF pacing and was significantly correlated with the time course of phase II V(O2). A significant compensatory amplitude response in heart rate (HR) was observed in addition to a higher (p < 0.05) deltaHR/V(O2) ratio during AV OFF. Ventilatory responses were consistent with ventilatory-perfusion mismatching and perceived exertion was higher during asynchronous pacing. CONCLUSION: This study demonstrated that the contribution of SVI affects V(O2) kinetics and underscores the importance of the atrial contribution to ventricular filling and, consequently, to metabolic and hemodynamic responses. This study supports the theory of an O2 transport limitation and further implicates SV as a potential limiting factor during sub-VT exercise intensities that are comparable to those encountered in activities of daily living.

Impact of a right ventricular impedance sensor on the cardiovascular responses to exercise in pacemaker dependent patients.

BACKGROUND: The evaluation of the heart rate (HR) response to exercise is important for the assessment of the rate response algorithm of sensor-controlled pacemakers. This study examined the effects of a right ventricular impedance sensor driven pacemaker on the cardiovascular responses to incremental exercise in pacemaker dependent patients. METHODS: Twelve patients (70.5 +/- 9.5 years; 5 Females: 7 Males) implanted with an Inos(2+) closed loop stimulation (CLS) pacemaker were compared to 12 healthy age and sex matched controls (70.6 +/- 4.8 years). All subjects performed the chronotropic assessment exercise protocol (CAEP). Variables of interest included HR, cardiac output (Q), oxygen uptake (VO2) and blood pressure (BP). Data were analyzed at rest, throughout exercise and during recovery. Furthermore, patient chronotropic responses were compared to a reference chronotropic response slope for aerobic exercise. RESULTS: There were no differences between groups for HR or Q response throughout exercise. At peak exercise, VO2 (mL x kg(-1) x min(-1)) was higher for the controls (p < 0.05). The patient chronotropic response slope was comparable to the CAEP reference slope from rest to both the anaerobic threshold (AT) and peak exercise. During recovery, no differences were observed between the groups for any parameters or for the HR decay slopes. CONCLUSION: Up to the anaerobic threshold, the right ventricular impedance sensor driven pacemaker delivered a pacing rate that contributed to an overall cardiovascular response similar to that observed in healthy age matched subjects.