Patients determined to understand how their pacemakers operate quickly realize medical and technological jargon stand in the way. In less than 50 years, technology has transformed the pacemaker from a simple, non-programmable device into a sophisticated machine with an array of programmable parameters. Despite the rapid development, pacemakers and their new features still operate on basic underlying principles. Industry innovations do add complexity, but jargon, not complexity, stands in the way of a patient's understanding.
Concerning Parameters
It is necessary to consider the purpose and components of a pacemaker system. The principal task of a pacemaker is to maintain the rhythmic cycle of a heart on an as-needed basis. Accomplishing such a task requires a system that can detect and respond to the presence or absence of a heart's natural rhythm. Two components are necessary to achieve this goal: the device---or, the central processing unit; and, the leads---thin wires implanted into the heart providing the link to the device. Following the implant of the components, programmable "parameters" establish the system and determine or limit how it operates. Regardless of the manufacturer, all pacemakers operate on these principles. Comprehending how parameters operate together provides a way around much of the jargon.
Basic Parameters
Basic parameters specify the pacing lead configuration and the lower rate settings. A pacemaker system consists of one or more leads, or wires, implanted in the heart. The number of leads attached to the device system limit the available parameter options. Each lead provides two essential sets of parameters: "output-pacing" and "input-sensing". Output-pacing defines the amount of energy delivered to the heart via the lead; whereas, input-sensing defines signals delivered to the device via the lead. The device then filters the input by processing allowed signals, and discarding unwanted signals. It is essential to note that both basic and extended parameters depend on accurate sense parameters for proper function, according to "Pacing and Clinical Electrophysiology." As long as the heart's natural rhythm maintains a rate above the "low-rate" parameter, the device will monitor and record the heart's activity on a beat-to-beat basis. Typically set to a rate between 60 to 80 beats per minute, the "base-rate" defines the slowest rhythm the device will allow.
Extended Parameters
Extended, or advanced parameters define the criteria for the pacemaker's diagnostic and automatic arrhythmia response functions. In other words, extended parameters record what the device sees and stores information on how the device reacts. Extended settings provide valuable feedback not only for device function but also disease progression. According to electrophysiologist Dr. David Scher of Pinnacle Health Systems, pacemaker diagnostic data have helped to identify pacing system malfunctions, and they have taken snapshots of clinically relevant arrhythmias to provide for early intervention that altered clinical outcomes.
Sensor Parameters
Sensor parameters relate to a separate device component called an activity sensor. Incorporated in all modern pacemakers, activity sensors respond to physical activity by dynamically increasing the heart rate in response to increasing physical intensity. Sensors provide three parameters: activity threshold, slope, and recovery. "Activity threshold" determines the level of exercise intensity required before the sensor will take over. The "slope" determines the speed at which the heart rate will increase during exercise. And, the "recovery" determines the speed at which the heart will return to the resting rate once exercise is complete.
References
- "Expert Review of Medical Devices"; New Developments in Anti-bradycardic Devices; Mortensen et al; May 2007
- "Pacing and Clinical Electrophysiology"; Efficacy and safety of bipolar sensing with high atrial sensitivity in dual chamber pacemakers; Wiegand et al; April 2000
- "Current Opinion in Cardiology"; Troubleshooting Pacemakers and Implantable Cardioverter-defibrillators; Scher; January 2004
