FMIS 105 CH5 Test #5 Pacemaker Rhythms and Malfunctions

Atrioventricular (AV) interval

The length of time between an atrial sensed/paced event and ventricular pacing stimulus.

Capture

The successful conduction of an artificial pacemaker's impulse through the myocardium, resulting in depolarization.

Escape interval

Time measured between a sensed cardiac event and the next pacemaker output.

Failure to capture

A pacemaker malfunction where the artificial stimulus is unable to depolarize the myocardium.

Failure to pace

A pacemaker malfunction where the device fails to deliver an electrical stimulus at its programmed time.

Oversensing

A pacemaker malfunction resulting from inappropriate sensing of extraneous electrical signals.

Paced interval

Period between two consecutive paced events in the same cardiac chamber.

Sensitivity

The extent to which an artificial pacemaker recognizes intrinsic cardiac electrical activity.

Threshold

The minimum amount of voltage (milliamperes) needed to obtain consistent capture.

Undersensing

A pacemaker malfunction where the device fails to recognize spontaneous myocardial depolarization.

Components of a pacemaker system

A pulse generator and pacing leads.

Pacing lead function

Carries electrical impulses to the heart and transmits electrical activity back to the pacemaker.

Temporary pacing routes

Transvenous, epicardial, or transcutaneous.

Transvenous pacing

Electrode introduced into a central vein to stimulate the endocardium of the right atrium/ventricle.

Epicardial pacing

Placement of pacing leads directly onto or through the epicardium during cardiac surgery.

Transcutaneous pacing (TCP)

Uses electrical stimulation through two pacing pads positioned on the patient's torso.

Indications for TCP

Significant bradycardia unresponsive to atropine, drug overdose, hyperkalemia, or as a bridge.

Primary limitation of TCP

Patient discomfort from skeletal muscle contraction and cutaneous nerve stimulation.

Cardiovascular implantable electronic devices (CIEDs)

The group name for permanent pacemakers and implantable cardioverter-defibrillators (ICDs).

Most common reason for permanent pacemakers

Bradycardia.

Electrode

The exposed portion of the pacing lead in direct contact with the heart.

Unipolar vs. Bipolar lead systems

Unipolar has one electrode at the tip; bipolar has positive and negative electrodes.

Leadless pacemaker

A self-contained generator and lead system inserted through the femoral vein into the right ventricle.

Fixed-rate pacemaker

Continuously discharges at a preset rate regardless of the patient's intrinsic heart rate.

Demand pacemaker

Discharges only when the patient's heart rate drops below the pacemaker's lower rate limit.

Electrical vs. Mechanical capture

Electrical is seen on the ECG; mechanical is assessed by palpating the patient's pulse.

Atrial pacing ECG appearance

Produces a pacemaker spike followed by a P wave.

Ventricular pacing ECG appearance

Produces a pacemaker spike followed by a wide QRS complex.

Pacemaker syndrome

AV asynchrony from ventricular demand pacing, causing decreased cardiac output and stroke volume.

Most common type of implanted pacemaker

Dual-chamber pacemaker (one lead in right atrium, one in right ventricle).

Atrial synchronous pacemaker (VDD)

Senses both chambers but paces only the ventricle; contraindicated in SA node disease.

AV sequential pacemaker (DVI)

Stimulates the right atrium then right ventricle, but senses only the ventricle.

Optimal sequential pacemaker (DDD)

Paces and senses both chambers, simulating the normal delay through the AV node.

Biventricular pacemaker

Has three leads (each ventricle and right atrium) to restore simultaneous ventricular contraction in heart failure.

ECG appearance of failure to pace

Absence of pacemaker spikes and a return of the underlying rhythm.

ECG appearance of failure to capture

Visible pacemaker spikes not followed by P waves or QRS complexes.

ECG appearance of undersensing

Pacemaker spikes occurring within P waves, within T waves, or too close behind QRS complexes.

ECG appearance of oversensing

Spikes at a rate slower than preset, or no paced beats despite slow intrinsic rate.

Most common cause of failure to sense

Displacement of the electrode tip.

Common causes of failure to capture

Displacement of pacing lead wire or output energy (mA) set too low.