Pacemaker syndrome

Complications

Studies have shown that patients with Pacemaker syndrome and/or with sick sinus syndrome are at higher risk of developing fatal complications that calls for the patients to be carefully monitored in the ICU. Complications include atrial fibrillation, thrombo-embolic events, and heart failure.^[7]

Risk factors

• 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.^[10]
• 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.^{[2][5][10][11]}
• 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.^{[5][7][10][12]}
• 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.^[5][10]

Loss of atrial contraction

Inappropriate pacing in patients with decreased ventricular compliance, which may be caused by diseases such as hypertensive cardiomyopathy, hypertrophic cardiomyopathy, restrictive cardiomyopathy, and aging, can result in loss of atrial contraction and significantly reduces cardiac output. Because in such cases the atrias are required to provide 50% of cardiac output, which normally provides only 15% - 25% of cardiac output.^[8][12]

Cannon A waves

Atrial contraction against a closed tricuspid valve can cause pulsation in the neck and abdomen, headache, cough, and jaw pain.^[8][10]

Increased atrial pressure

Ventricular pacing is associated with elevated right and left atrial pressures, as well as elevated pulmonary venous and pulmonary arterial pressures, which can lead to symptomatic pulmonary and hepatic congestion.^[5]

Increased production of natriuretic peptides

Patients with pacemaker syndrome exhibit increased plasma levels of ANP. That's due to increase in left atrial pressure and left ventricular filling pressure, which is due to decreased cardiac output caused by dyssynchrony in atrial and ventricular contraction. ANP and BNP are potent arterial and venous vasodilators that can override carotid and aortic baroreceptor reflexes attempting to compensate for decreased blood pressure. Usually patients with cannon a waves have higher plasma levels of ANP than those without cannon a waves.^[1][13][14]

VA conduction

A major cause of AV dyssynchrony is VA conduction. VA conduction, sometimes referred to as retrograde conduction, leads to delayed, nonphysiologic timing of atrial contraction in relation to ventricular contraction. Nevertheless, many conditions other than VA conduction promote AV dyssynchrony.^{[1][2][4][8][10]}

This will further decrease blood pressure, and secondary increase in ANP and BNP.^[13][14]

Diet

Diet alone cannot treat pacemaker syndrome, but an appropriate diet to the patient, in addition to the other treatment regimens mentioned, can improve the patient's symptoms. Several cases mentioned below:

• For patients with heart failure, low-salt diet is indicated.^[15]
• For patients with autonomic insufficiency, a high-salt diet may be appropriate.^[15]
• For patients with dehydration, oral fluid rehydration is needed.^[15]

Medication

No specific drugs are used to treat pacemaker syndrome directly because treatment consists of upgrading or reprogramming the pacemaker.^[15]

Medical care

• For some patients who are ventricularly paced, usually the addition of an atrial lead and optimizing the AV synchrony usually resolves symptoms.^{[1][4][8][10]}
• In patients with other pacing modes, other than ventricular pacing, symptoms usually resolve after adjusting and reprogramming of pacemaker parameters, such as tuning the AV delay, changing the postventricular atrial refractory period, the sensing level, and pacing threshold voltage. The optimal values of these parameters for each individual differ. So, achieving the optimal values is by experimenting with successive reprogramming and measurement of relevant parameters, such as blood pressure, cardiac output, and total peripheral resistance, as well as observations of symptomatology.^{[1][4][8][10]}
• In rare instances, using hysteresis to help maintain AV synchrony can help alleviate symptoms in ventricularly inhibited paced (VVI) patients providing they have intact sinus node function. Hysteresis reduces the amount of time spent in pacing mode, which can relieve symptoms, particularly when the pacing mode is generating AV dyssynchrony.^[4][10]
• If symptoms persist after all these treatment modalities, replacing the pacemaker itself is sometimes beneficial and can alleviate symptoms.^[1][4][8]
• Medical care includes supportive treatment, in case any of the following complications happen, medical team should be ready. Possible complications include heart failure, hypotension, tachycardia, tachypnea, and oxygenation deficit.^[1][6][8]

Surgical care

Sometimes surgical intervention is needed. After consulting an electrophysiologist, possibly an additional pacemaker lead placement is needed, which eventually relieve some of the symptoms.^[1][4]