Effect of Paced HR on Central BP

Central (aortic) blood pressure predicts heart, brain and kidney complications more reliably than the usual peripherally measured blood pressure. Heart rate has a strong and sometimes counter-intuitive influence on central blood pressure. Pacemakers implanted due to sick sinus syndrome (SSS) are typically programmed anywhere between 55-75 beats per minute (bpm), yet it is unclear which rate gives hypertensive pacemaker recipients the most favourable central hemodynamics. This single-center, randomized, single-blind, two-period cross-over trial will enrol 20 adults (18-80 years) who already carry a dual-chamber pacemaker for SSS, are in sinus rhythm, and have medication-controlled arterial hypertension. Each participant will complete two eight-week pacing periods in random order: * "Slow" period - pacemaker lower-rate set to 55 bpm. * "Fast" period - pacemaker lower-rate set to 75 bpm. A two-week wash-out at the device's usual settings separates the periods. At baseline and after each intervention the team will perform non-invasive pulse-wave analysis (SphygmoCor XCEL) to obtain central systolic blood pressure (primary endpoint) and arterial stiffness indices such as augmentation index and pulse-wave velocity (secondary endpoints). Pacemaker function, symptoms and safety events are reviewed at every visit; settings can be adjusted by ±5 bpm if troublesome symptoms occur. The study will provide the first long-term evidence on how fixed pacing rates modulate central blood pressure in real-world SSS patients with hypertension, potentially guiding clinicians toward the optimal programming strategy.