HHE Cardiovascular supplement 2018 - Page 12

design has improved to provide greater stability at the interface with the myocardium, and less susceptibility to fl exion damage. Where Arne Larsson’s fi rst device provided only one pacing mode – asynchronous VOO pacing – modern microprocessor-driven devices are increasingly sophisticated and can employ various algorithms to optimise the pacing mode, depending on the patient’s needs. 2 Today, permanent pacemaker implantation has become routine for bradyarrhythmia management. Worldwide, more than 700,000 pacemakers are implanted annually, with around 35,000 implanted in the UK. 3,4 Although it has become a routine procedure and is very safe for most patients, problems relating to the leads, venous access or the pocket may occur. In the immediate- to short-term, the most signifi cant potential complications include haematoma, pneumothorax, lead displacement or, rarely, cardiac perforation and tamponade. 5 Device infection, which in turn may lead to septicaemia and endocarditis, carries a mortality of up to 35% and normally warrants device extraction, with its own inherent risk of myocardial or vascular injury. 6 Other, longer-term complications, such as chronic lead failure from insulation damage or lead fracture, warrant a repeat procedure to replace the faulty lead. The risk of complications increases with the number of procedures required during a patient’s lifetime. A pacemaker recipient in his/her early 50s, for example, might expect to have a further three of four battery change procedures on top of the initial implantation, and with each opening of the pocket, the risk of infection rises. Leadless pacemakers Although there have been continuous developments in pacemaker technology over the last 60 years, a standard transvenous pacemaker today consists, in essence, of the same components it ever has: a pulse generator, including battery and circuitry, and at least one lead to deliver an electrical stimulus to the myocardium and to transmit any signals of intrinsic myocardial electrical activity back to the generator. Table 1 Characteristics of the Nanostim™ LCP, Micra™ TPS and single chamber transvenous system Parameter Nanostim™ LCP Micra™ TPS Dimensions (mm) Volume (cm 3 ) Weight (g) Fixation mechanism 42 x 5.99 1.0 2.0 Screw-in helix 25.9 x 6.7 0.8 2.0 Four nitinol tines Polarity Estimated battery longevity • Standard settings* • Alternative settings† Major complications overall Hospitalisation System revision Cardiac injury Access site complication Bipolar Bipolar Single chamber transvenous system (Medtronic Azure S SR MRI SureScan) 42.6 x 50.8 x 7.4 12.25 22.5 Active lead: screw-in helix Passive lead: tines Bipolar or unipolar 9.8 years 14.7 years 6.7% 4.7 years 9.6 years 4.0% 14.3 years – 7.4% – 1.9% 1.6% 1.2% 2.3% 0.4% 1.6% 0.7 3.9% 3.5% 1.1% 1.6% * Longevity based on fi xed programming at the ISO International Organisation for Standardisation (ISO 14708) standard guidelines for reporting pacemaker battery duration longevity: 2.5V, 0.4ms, 600 Ω, 60 beats/min, 100% pacing. † Longevity based on nominal settings: 1.5V, 0.24ms, 500 Ω, 60 beats/min, 100% pacing LCP Leadless cardiac pacemaker TCP Transcatheter pacing system 12 HHE 2018 | hospitalhealthcare.com Figure 2 A standard single chamber pacemaker with the Micra™ Transcatheter Pacing System. Reproduced with permission of Medtronic, Inc.