This is a randomized controlled single-centre clinical trial with a cross-over design to compare non-invasively evaluated central blood pressure and related parametres in sick sinus syndrome patients with hypertension who are paced long-term at a slower vs faster heart rate

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