Study Population
We identified patients 18 years or older undergoing elective right and left heart catheterization and capable of providing informed consent. Major exclusion criteria were as follows: age less than 18 years, unable to provide informed consent, any form of atrial fibrillation, presence of implantable cardiac pacemaker and acute coronary syndrome, cardiac tamponade, cardiogenic shock, massive pulmonary embolism, or any other medical unstable emergency as an indication for cardiac catheterization procedure.