P

P wave. (1)An intrinsic atrial event. (2) The portion of the ECG representing atrial depolarization.

Pacemaker. (1) Devices. The system composed of the pulse generator and the connected lead(s). In common usage, pulse generator is synonymous with pacemaker. (2) Physiology. Any portion of the heart which initiates the electrical impulses that control the heart rate; in the healthy heart, this is the SA node. In pacing, a physiological pacemaker is often called a natural pacemaker.

Pacemaker-dependent patient. A patient who needs a pacemaker to maintain proper cardiac rhythm to sustain adequate cardiac output sufficient for the activities of daily living. Such an individual may have little or no underlying intrinsic rhythm.

Pacemaker EGG. An ECG from a patient being artificially paced. Pacemaker ECGs are usually characterized by the presence of pacemaker spikes.

Pacemaker-induced arrhythmia. A type of dysrhythmia, usually a tachycardia, induced by competition between the paced and native rhythms. Its induction may be inadvertent or intentional, as in an EP lab. Once initiated, the pacemaker-induced arrhythmia is sustained without the continued participation of the pacemaker.

Pacemaker-mediated tachycardia. A tachycardia induced by competition between the paced and native rhythms and sustained by the continued participation of the pacemaker. A common example of pacemaker-mediated tachycardia is an endless loop tachycardia. and, rarely, intrinsic loops within the pacemaker. Abbreviated PMT. Also known as endless loop tachycardia, pacemaker reentry tachycardia or circus tachycardia.

Pacemaker Mediated Tachycardia (PMT). A reentrant arrhythmia in which the dual chamber pacemaker acts as the anterograde limb of the tachycardia and the natural conduction path as the retrograde limb. A rapid paced rhythm that can occur with atrial tracking pacemakers. It begins with the loss of A-V synchrony and is sustained by ventricular events that are conducted retrogradely to the atria. The pacemaker senses this retrograde atrial depolarization and then delivers a stimulus to the ventricle. Also known as endless less loop tachycardia. Other examples include tracking atrial fibrillation or flutter

Pacemaker reentry tachycardia. circus tachycardia or pacemaker mediated tachycardia.

Pacemaker syndrome. Adverse hemodynamic or electrophysiologic consequences, or both, associated with an electrically normal pacing system. Pacemaker syndrome may induce symptoms ranging from minor to severe or may simply limit the patient's ability to achieve an optimal functional status. While most commonly associated with the loss of AV synchrony, it may also occur because of an inappropriate AV interval or inappropriate rate modulation. It may be intermittent or persistent, but will only be present during a paced rhythm.

Pacing configuration. The polarity (unipolar or bipolar) with which a pacemaker will stimulate. Many modern pulse generators offer programmable pacing configuration. Sometimes called pulse configuration. See also programmable polarity.

Pacing interval. The time period between two consecutive paced events without an intervening sensed event. It is expressed in milliseconds (AA interval, VV interval) Also known as automatic interval, demand interval or basic interval.

Pacing state. Refers to the primary states (or event combinations) of DDD pacing. These are PV (sensed P wave followed by a ventricular output pulse), PR (sensed P wave followed by a sensed R wave), AV (atrial pulse followed by a ventricular output pulse), AR (atrial output pulse followed by a sensed R wave). PVE (premature ventricular event) is sometimes included as a pacing state.

Pacing stimulus. (1)The output pulse from the pacemaker. (2) The mark representing the pacemaker's electrical output recorded by the EGG. Also known as output pulse. See also artifact.

Pacing system. The implanted pulse generator, implanted lead(s) and programmer, taken together as one system, plus the patient.

Pacing system analyzer. An external testing and measuring device capable of pacing the heart during pacemaker implantation and measuring such things as the stimulation and sensing thresholds and lead impedance. Pacing system analyzers may also have the capability of testing pulse generator function prior to implant, measuring slew rate or printing an electrogram of a sensed QRS complex. Abbreviated PSA.

Parameter. A distinguishable value that can be measured and sometimes changed, either indirectly or directly. In pacing, parameter refers to a value that influences the function of the pacemaker, such as mode, base rate, pulse width, pulse amplitude, sensitivity and so on.

Parasympathetic nervous system. Part of the autonomic nervous system involved in the control of involuntary bodily functions, including control of cardiac and blood vessel activity. Stimulation of certain parasympathetic nerves causes the SA node to discharge at a slower rate and slows conduction through the AV node, which, in turn, extends the PR interval. See also autonomic nervous system and sympathetic nervous system.

Paroxysmal. Pertaining to a sudden, periodic recurrence or worsening of disease symptoms.

Paroxysmal supraventricular tachycardia. Type of rapid atrial arrhythmia characterized by brief periods of sudden-onset and often abrupt termination of atrial tachycardia. The sudden onset of the tachycardia is caused by micro-reentry within the AV node or macro-reentry between the AV node and a bypass tract. Abbreviated PSVT. Sometimes called paroxysmal atrial tachycardia, AV nodal reentry tachycardia or AV reentry tachycardia.

Passive fixation lead. A pacing lead with an attachment mechanism such as fins or tines which allow them to lodge in the trabeculae lining the inner wall of the heart without actually penetrating the cardiac wall. See also active fixation lead.

Peak amplitude. A general term for the greatest amplitude of a waveform, measured from baseline to highest point of wave. percutaneous. Literally "through the skin." In pacing, endocardial leads are inserted through the skin into a blood vessel, then advanced into the heart.

Percutaneous introducer. A thin, hollow tube used for easy passage of the endocardial lead through the skin into a blood vessel, then advancing the lead into the heart.

Permanent lead. Any implanted pacing lead intended for long-term use.

Phantom programming. A general term for any inadvertent or unintentional programming of a pulse generator. Phantom programming may be caused by electromagnetic interference in the environment affecting programming or it may be due to an intentional reprogramming of the pulse generator which had not been recorded in the patient's record.

Phrenic nerve. The nerve controlling the rhythmic contraction of the diaphragm.

Physiological refractoriness. The normal period during which cardiac tissue will not respond to a stimulus, meaning that cardiac tissue will not conduct or contract during this time.

Pocket. The subcutaneous pouch in which the pulse generator is inserted at implant.

Pocket stimulation. Stimulation of muscle tissue surrounding the implanted pulse generator. Pocket stimulation may occur in a unipolar system owing to the concentration of current flow at the pulse generator case (the anode). Another potential cause of pocket stimulation is a defect in the lead insulation, which could occur with either a unipolar or a bipolar pulse generator.

Polarity. Pertaining to the electrode configuration of a lead or the operating configuration of a pulse generator. Polarity is either unipolar or bipolar. It is possible in some advanced programmable polarity pulse generators to pace in one polarity and sense in another. Note that a bipolar lead (having two electrodes) can pace or sense in either a unipolar or bipolar manner, while a unipolar lead (having one electrode only) can pace or sense only in a unipolar manner.

Polymorphic tachycardia. A tachycardia that originates from more than one focus. On an EGG, the QRS complex will exhibit a variety of different morphologies.

Polyurethane. A synthetic resin polymer used as insulation material in some pacing leads.

Post-ventricular atrial refractory period (PVARP). One of the timing cycles in dual-chamber pacemakers during which the atrial channel's sensing circuitry is rendered unresponsive. Initiated by a sensed or ventricular paced event and ending with an atrial sensed or paced event, the post-ventricular atrial refractory period is intended to prevent the atrial sense amplifier from sensing farfield ventricular signals. Therefore, the post-ventricular atrial refractory period may be considered the atrial equivalent of the ventricular blanking period. The post-ventricular atrial refractory period is usually a programmable parameter; if sufficiently long, it can prevent the atrial channel from responding to premature atrial contractions or retrograde atrial depolarizations and thus prevent pacemaker-mediated tachycardias. Abbreviated PVARP.

PPM. Abbreviation for pulses per minute. The abbreviation ppm usually refers to the paced rate, while beats per minute (BPM) refers to an intrinsic heart rate. See also bpm.

PR. One of the four normal pacing states in DDD and DDDR pacing, starting with an atrial sensed event (P) and ending with a ventricular sensed event (R). See also pacing state.

PR interval. (1)The interval corresponding to the PR pacing state. (2) The period of time, measured in milliseconds and readily viewed on a surface EGG, from the onset of the P wave (atrial depolarization) to the onset of the QRS complex (ventricular depolarization).

Presyncope. The sensation of almost fainting but without total loss of consciousness. Sometimes called near-syncope.

Programmability. The characteristic of most modern pulse generators allowing one or more parameters to be adjusted noninvasively before, during or after implantation. Also known as multiprogrammability.

Programmable polarity. A feature of pacemakers in which the polarity configuration for pacing and/or sensing (unipolar or bipolar) may be programmed. In some pacemakers, it is possible to program sensing and pacing polarity independently (i.e. to pace unipolar but sense bipolar or vice versa).

Proximal. Nearest the point of reference. On pacing lead connectors, the proximal electrode is the ring electrode. See also distal. pseudofusion beat. A spontaneous cardiac depolarization occurring at or near a pulse generator output pulse. Because the stimulus occurs after the heart has spontaneously depolarized, the pacemaker output is ineffective, but it distorts the morphology of the complex on the EGG. See also pseudopseudofusion beat.

Pseudomalfunction. (1)An unexpected behavior of the pacemaker which may appear to be the result of a malfunction but which is actually normal behavior for that device under those programmed settings. Pseudomalfunctions are often eccentric or unusual behaviors. (2) Normal pacing system function which is misinterpreted as a pacing system problem due to a recording system problem or artifact.

Pseudopseudofusion beat. An electrocardiographic superimposition of an atrial stimulus on the native QRS complex. The atrial output pulse cannot contribute to the ventricular contraction. Pseudopseudofusion beats can occur only in dual-chamber pacing modes and are most common in DVI. See also pseudofusion beat.

Pulse amplitude. The height of the output pulse as expressed in volts or milliamperes.

Pulse duration. See pulse width.

Pulse generator. The implantable device that contains the battery, circuitry and other components which provide the output stimuli. The pulse generator and the lead(s) together make up the pacemaker, although in informal use, pulse generator and pacemaker are used as synonyms.

Pulse pressure. The difference between the systolic and diastolic blood pressures.

Pulse width. The length of time, measured in milliseconds, that the output pulse is delivered. Pacemaker output is usually defined in terms of voltage (pulse amplitude) and milliseconds (pulse width). Pulse width is measured from the leading edge to the trailing edge of the wave. Also known as pulse duration.

Pulses per minute. The standard unit of measure for paced rate. Abbreviated ppm.

PV. One of the four normal pacing states in DDD and DDDR pacing, starting with an atrial sensed event and ending with a ventricular paced event. See also pacing state.

PV interval. The time period from the onset of the P wave (atrial depolarization) to the ventricular pacing stimulus.

PVARP. Abbreviation for post-ventricular atrial refractory period.