Long-term Atrial Pacing and Central Blood Pressure

Inclusion Criteria: * age 18-80 years * sick sinus syndrome * permanent cardiac pacemaker with right atrial and right ventricular leads * at least 3 months from implantation * sinus rhythm * percentage of atrial pacing at or above 80% since last interrogation * percentage of ventricular pacing at or below 3% since last interrogation * primary arterial hypertension * antihypertensive drug treatment * mean office brachial blood pressure below 140/90 mmHg * mean home brachial blood pressure below 135/85 mmHg * ability to understand and follow study protocol * signed informed consent form Exclusion Criteria: * inclusion criteria not fulfilled * violation of study protocol by subject, investigator or third part * high quality central hemodynamic measurements cannot be perfomed * inter-arm difference in brachial systolic blood pressure 15 mmHg or above * intrinsic QRS complex 130 ms or above * more than three antihypertensive agents in use * treatment with digoxin or agents from Vaughan-Williams classes Ic, III või IV * frequent high atrial rate episodes * coronary artery disease * secondary hypertension * resistant hypertension * orthostatic hypotension * heart failure with decreased or preserved left ventricular ejection fraction * implantable cardioverter-defibrillator or cardiac resynchronization therapy * significant valvular heart disease * significant congenital heart disease * body mass index ≥35 kg/m2 * type I diabetes * type II diabetes with cardiovascular complications or on insulin therapy * other significant endocrine disease * history of cerebrovascular attack * carotid artery disease * lower extremity arterial disease * severe chronic obstructive pulmonary disease * severe asthma * severe sleep apnea * interstitial pulmonary disease * inhaled beta adrenergic agonist therapy * active cancer treatment * central nervous system degenerative disease * systemic connective tissue disease * abnormal TSH at present * glomerular filtration rate ≤30 ml/min/m2 * hemoglobin \<100 g/L (female), \<110 g/L (male) * hepatic dysfunction * alcohol abuse * pregnancy or breastfeeding * no health insurance provided by Estonian Health Insurance Fund * withdrawal of informed consent * loss of contact with a subject during study