/Sinus Node Dysfunction Treatment & Managemen

Sinus Node Dysfunction Treatment & Managemen

Approach Considerations

The only effective medical care in patients with sinus node dysfunction (SND) is correction of extrinsic causes.

No treatment is required for asymptomatic patients, even if they have abnormal SNRTs or SACTs. If the patient is receiving medications that can provoke sinus bradyarrhythmias (eg, beta-blockers, angiotensin-converting enzyme [ACE] inhibitors), the medications should be stopped if possible.

Acute treatment consists of atropine (0.04 mg/kg intravenously every 2-4 h) and/or isoproterenol (0.05-0.5 mcg/kg/min intravenously). A transvenous temporary pacemaker sometimes is required despite medical therapy.

In patients with bradyarrhythmias-tachyarrhythmias, the tachyarrhythmias may be controlled with digoxin, propranolol, or quinidine. However, these patients should be monitored closely with frequent Holter monitoring to ensure that the bradyarrhythmias are not exacerbated or causing symptoms (eg, dizziness, syncope, CHF); if this is the case, permanent pacemaker therapy is also required.

Inpatient care

Admit patients for testing and pacemaker placement when indicated.

Diet

Patients with vasovagal syncope may require increased dietary salt intake.

Activity

Patients with symptomatic SND who are not on pacemaker therapy should titrate their level of activity to minimize symptoms.

Consultations

These include cardiac electrophysiology consultation.

Transfer

Transfer patients for complicated dysrhythmias and pacemaker implant.

Pacemaker Therapy

Pacemaker therapy is the only effective surgical care for patients with chronic, symptomatic SND.

Because the incidence of sudden death in patients with SND is extremely low and pacemaker therapy does not appear to affect survival, the major goal of pacemaker therapy in patients with SND is to relieve symptoms.

Pacemaker indications

According to the 2008 ACC/AHA/HRS guidelines (updated in 2013), pacemaker therapy has the following indications [2, 3] :

  • Class I indication – For patients with documented symptomatic sinus bradycardia, sinus pause, and chronotropic incompetence; this includes patients who have iatrogenic SND secondary to essential medications for which no acceptable alternatives exist
  • Class IIa indication – For patients with SND and a sinus rate below 40 bpm when a clear association between symptoms (ie, symptoms consistent with bradycardia) and bradycardia has not been documented
  • Class IIa indication – For patients with syncope of unexplained origin when clinically significant abnormalities of SN are discovered or provoked in EP studies
  • Class IIb indication – For patients with minimal symptoms and a chronic heart rate of less than 40 bpm while awake
  • Class III indication – Pacemaker therapy is contraindicated in patients with asymptomatic SND or symptomatic bradycardia due to medications that are not essential.

In 2013, the European Society of Cardiology (ESC) published clinical practice guidelines on cardiac pacing and cardiac resynchronization therapy. [28]

Single- versus dual-chamber pacemakers

In patients with SND, the annual incidence of complete heart block is about 0.6%. [29] In the United States, the implantation of dual-chamber pacemakers is preferred in practice because their use anticipates the possible subsequent development of conducting system dysfunction.

This practice is supported by data from the Danish Multicenter Randomized Trial on Single Lead Atrial Pacing versus Dual Chamber Pacing in Sick Sinus Syndrome (DANPACE) trial, in which 9.3% of patients with single-lead atrial pacing (AAIR) required upgrade to a dual-chamber pacemaker (DDDR) over 5.4 years follow-up due to new development of significant AV conduction abnormalities. This was necessary despite the fact that these patients had no significant intraventricular conduction abnormality, PR intervals below 260ms, and no Wenckebach AV block with atrial pacing at 100 bpm at baseline. [30]

In addition, patients in AAIR mode had more atrial fibrillation than did patients in DDDR mode. Importantly, however, no significant mortality difference between AAIR and DDDR mode was noted.

Arguably, a single-chamber atrial pacemaker with AAI mode is an acceptable alternative in patients with SND and normal AV and intraventricular conduction because of the added expense of and the potential for more lead extraction with a dual-chamber pacemaker.

In patients with SND and known AV conduction abnormality (including bundle branch block and bifascicular block), a dual-chamber pacemaker should be used due to the high risk of AV block (about 36% in a 5-year follow-up study).

Pacemaker programming features

Chronic right ventricular pacing has been shown to be associated with an increased incidence of atrial fibrillation, stroke, heart failure, and probably death. [18, 31, 32] A study suggested that RV pacing is detrimental to left ventricular (LV) function even in patients with a normal LV ejection fraction (LVEF). [33] Therefore, avoiding RV pacing is advantageous in patients with SND treated with pacemaker therapy.

However, using the intrinsic AV conduction in patients with a very long intrinsic PR interval may not be beneficial clinically, as suggested by a trial in patients with an intracardiac defibrillator (ICD). [30] Theoretically, a very long PR interval may result in pacemaker syndrome during sinus tachycardia or fast atrial pacing rhythm.

In the DANPACE trial, about 65% of patients with a moderate AV delay setting in DDDR mode with mean RV pacing had less atrial fibrillation and no increased rate of heart failure, as compared with patients in AAIR mode. Clearly, the optimal AV delay settings in patients with SND are still unknown, although various programming algorithms from different pacemaker companies are very effective in reducing RV pacing.

Mode switch is an important feature to monitor atrial flutter and fibrillation events. Because more than 50% of patients with SND may over time develop tachy-brady syndrome, [18] it is very important to identify these patients through pacemaker monitoring and anticoagulate them to reduce their risk of stroke. However, the most appropriate anticoagulant therapy is still uncertain for patients in whom atrial fibrillation is detected only as an incidental finding on pacemaker or ICD diagnostics.

Pacemakers with a rate drop response program may benefit some patients with neurocardiogenic syncope. Studies have suggested that closed-loop stimulation technique in the Biotronik pacemaker may be quite helpful in reducing syncope in patients with neurocardiogenic syncope. [34, 35]

Rate response features have been used in patients with SND, especially in the presence of chronotropic incompetence. However, the clinical benefits of this program feature are still controversial. [36]

Long-Term Monitoring

Asymptomatic patients with SND should be observed for symptoms. In patients with a pacemaker, carry out the following on routine pacemaker interrogations:

  • Monitor leads and battery status
  • Ensure adequate heart rate support at rest, during daily activities, and during exercise
  • Monitor for pacemaker malfunction, such as pacemaker-mediated tachycardia
  • Ensure minimal RV pacing.
  • Monitor for atrial fibrillation and atrial flutter events

Pregnancy

Patients with SND who become pregnant and take antiarrhythmic medications should have their levels measured because they frequently require adjustment. In addition, medication with teratogenic effects (eg, amiodarone, which is associated with fetal thyroid dysfunction) should be replaced, if possible.

Patients with SND who become pregnant and have a pacemaker are advised to perform frequent pacemaker checks and make the appropriate adjustments (especially when an increase in the lead’s threshold is noted).

Patients with SND who become pregnant and have ventricular dysfunction due to cardiomyopathy or a Mustard or Fontan procedure should have regular and close medical follow-ups with the obstetrician and cardiologist. This permits appropriate adjustment and implementation of anti-CHF medication. If the CHF progresses despite medical management and becomes intractable, the mother and fetus are at risk and early delivery may be scheduled.