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DDDR. NBG code for dual-chamber pacing with atrial tracking and rate modulation.

DDDRD. NBG code for DDDR pacing with the added capability of dual antitachycardia responses, both antitachycardia pacing and delivery of a high-energy shock (cardioversion and defibrillation).

DDI. NBG code for dual-chamber, nontracking pacing, with sensing in both chambers. Pacing and sensing occur in both atrium and ventricle, with inhibited response.

DDIR. The NBG code for dual-chamber, nontracking pacing with sensing in both chambers and rate modulation.

Defibrillation. The termination of atrial or ventricular fibrillation, usually using electrical energy delivered to the heart through chest-wall electrodes, directly to the heart during open-heart surgery, or through an automatic implantable defibrillator.

Demand. Any pacing mode or pacemaker that delivers an output pulse only when necessary, that is, when the intrinsic rate is less than the programmed base rate.

Demand interval. The time period between two consecutive paced events in the same chamber without an intervening sensed event. It is expressed in milliseconds (AA interval, VV interval). Also known as basic interval or pacing interval. demand rate. The rate (in ppm) defined by the demand interval (in milliseconds).

Depletion indicator. A function of the pacemaker showing that the battery is wearing out and pulse generator replacement should be scheduled.

Depolarization. The sudden change in electrical potential from negative to slightly positive which occurs during phase O of the action potential. In the heart, electrical depolarization initiates the mechanical contraction. Waves of depolarization spread from cell to cell. When this occurs in the atria, a native P wave is seen on the EGG; when this occurs in the ventricles, this is seen as a native QRS complex on the EGG. Depolarization can also be initiated by a pacemaker output stimulus.

Diaphragmatic stimulation. Electrical activation of the diaphragm muscle by the pacemaker output pulse. The abrupt diaphragmatic contraction is noted clinically as hiccups associated with each pacing stimulus. The pacing stimulus may stimulate the diaphragm either directly or indirectly via the phrenic nerve.

Distal. Farthest from the point of reference. On pacing lead connectors, the distal electrode is the tip electrode. See also proximal.

DOO. The NBG code for dual-chamber asynchronous pacing.

DOOR. The NBG code for dual chamber asynchronous pacing with rate modulation.

Dual chamber. Refers to a pacing mode or pulse generator capable of pacing and/or sensing in the atrium and pacing and/or sensing in the ventricle. Examples of dual-chamber modes are VAT, VDD, DVI, DDI and DDD.

Dual Chamber Pacing. Pacing in both the atria and the ventricles to artificially restore the natural contraction sequence of the heart. Also called ‘physiologic” or “universal” pacing.

DVI. The NBG code for AV sequential pacing. Pacing occurs in the atrium and ventricle, but sensing occurs only in the ventricle and the response to sensing is inhibition.

DVIR. The NBG code for AV sequential pacing with rate modulation.

Dysrhythmia. Any disturbance in the normal cardiac rhythm, possibly resulting from abnormal origination, discharge or conduction of the electrical impulses. In common usage, it is synonymous with arrhythmia, although in the strictest sense, arrhythmia is the absence of cardiac rhythm and dysrhythmia is an abnormal cardiac rhythm.