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Pacemaker syndrome is a condition that represents the clinical consequences of suboptimal atrioventricular (AV) synchrony or AV dyssynchrony after pacemaker implantation. It is an iatrogenic disease—an adverse effect resulting from medical treatment—that is often underdiagnosed. AV dyssynchrony occurs when timing of atrial contraction occurs too close to the pacemaker conducted ventricular contraction. In general, the symptoms of Pacemaker syndrome are a combination of decreased cardiac output, loss of atrial contribution to ventricular filling, loss of total peripheral resistance response with marked decreases in blood pressure, along with non-physiologic pressure waves.

Individuals with a low heart rate prior to pacemaker implantation are more at risk of developing pacemaker syndrome. Normally the first chamber of the heart (atrium) contracts as the second chamber (ventricle) is relaxed, allowing the ventricle to fill before it contracts, and blood to be pumped out of the heart. When the timing between the two chambers us unsynchronized, less blood is delivered on each beat. Patients who develop pacemaker syndrome may require adjustment of the pacemaker, or fitting of another lead to better coordinate the timing of atrial and ventricular contraction.

Signs and symptoms[edit]
No specific set of criteria has been developed for diagnosis of pacemaker syndrome. Most of the signs and symptoms of pacemaker syndrome are nonspecific, and many are prevalent in the elderly population at baseline. In the lab, pacemaker interrogation plays a crucial role in determining if the pacemaker mode had any contribution to symptoms.

Symptoms commonly documented in patients history, classified according to cause :


 * Neurological - Dizziness, syncopal episodes, and confusion, fatigue
 * Heart failure - Exertional dyspnea, decreased activity tolerance, orthopnea, paroxysmal nocturnal dyspnea, and edema.
 * Hypotension - Seizure, mental status change, diaphoresis, and signs of orthostatic hypotension and shock.
 * Low cardiac output - Fatigue, weakness, dyspnea on exertion, lethargy, and lightheadedness.
 * Hemodynamic - Pulsation in the neck and abdomen, choking sensation, jaw pain, right upper quadrant (RUQ) pain, chest colds, and headache.
 * Heart rate related - Palpitations associated with arrhythmias

In particular, the examiner should look for the following in the physical examination, as these are frequent findings at the time of admission :


 * Vital signs may reveal hypotension, tachycardia, tachypnea, or low oxygen saturation.
 * Pulse amplitude may vary, and blood pressure may fluctuate.
 * Neck vein distension and pulsation and cannon waves in the neck veins.
 * Lungs may exhibit crackles.
 * Cardiac examination may reveal regurgitant murmurs and variability of heart sounds.
 * Liver may be pulsatile in severe cases, RUQ tenderness with palpation, ascites may be present in severe cases.
 * Lower extremities edema.
 * Neurologic examination may reveal confusion, dizziness, or altered mental status.

Complications[edit]
Studies have shown that patients with Pacemaker syndrome and/or with sick sinus syndrome are at higher risk of developing fatal complications. These patients should be monitored closely during treatment of complications, typically in the intensive care setting. Complications include atrial fibrillation, thrombo-embolic events, and heart failure. Complications can impact the patients overall quality of life.

Causes

The cause is poorly understood. However several risk factors are associated with pacemaker syndrome.

Risk factors[edit]

 * In the preimplantation period, two variables are predicted to predispose to the syndrome. First is low sinus rate, and second is a higher programmed lower rate limit. In postimplantation, an increased percentage of ventricular paced beats is the only variable that significantly predicts development of pacemaker syndrome.
 * Patients with intact VA conduction are at greater risk for developing pacemaker syndrome. Around 90% of patients with preserved AV conduction have intact VA conduction, and about 30-40% of patients with complete AV block have preserved VA conduction. Intact VA conduction may not be apparent at the time of pacemaker implantation or even may develop at any time after implantation.
 * Patients with noncompliant ventricles and diastolic dysfunction are particularly sensitive to loss of atrial contribution to ventricular filling and have a greater chance of developing the syndrome. This includes patients with cardiomyopathy (hypertensive, hypertrophic, restrictive) and elderly individuals.
 * Other factors correlated with development of pacemaker syndrome include decreased stroke volume, decreased cardiac output, and decreased left atrial total emptying fraction associated with ventricular pacing.