For prognostic reasons, pacemaker implantation should also be recommended to asymptomatic patients with AVB II° type Mobitz or AVB III°. Sinus node disease (e.g., SA block, sinus bradycardia) generally has a good prognosis and requires pacing therapy only in symptomatic bradycardia. Functional bradycardias generally do not require pacemaker therapy, as does an AVB I° or AVB II° type Wenckebach. The most common reversible causes of bradycardia are bradycardic drugs, myocardial ischemia, intoxications, and electrolyte disturbances. In cases of unclear power intolerance or heart failure, attention must be paid to an AVB type 2:1, because P waves localized in the T wave can easily be missed.
The standard therapy of irreversible symptomatic bradycardic arrhythmias is pacemaker implantation. In 2015, 5170 pacemakers were implanted in Switzerland alone. The mean age of patients at initial implantation was 77 years [1].
There are now also electrodeless pacing systems (Fig. 1), which, in contrast to conventional pacemakers, are placed in the right ventricle via the femoral vein . However, the use of these single-chamber devices is reserved for a limited patient population. According to initial data, leadless devices can be considered safe and feasible [2].
Etiology of bradycardia
In 88.5% of pacemaker implantations, the etiology of bradycardia remains unknown [1]. Bradycardic medications should be stopped if possible. It should be noted that local forms of application may also have a systemic effect (for example, the beta-blocker timolol in eye drops). Some noncardiac medications can also cause AV conduction disturbances-they are listed in Table 1 In summary. A common treatable cause of sinus node dysfunction or AV conduction abnormalities is coronary ischemia, which should be sought and treated if ischemia-typical symptoms or appropriate risk profile are present [3]. Intoxications or electrolyte disturbances, especially hyperkalemia, also cause bradycardia. If Lyme disease is clinically suspected, B. burgdorferi IgM and IgG (ELISA as a screening test, Western blot as a confirmatory test) can be determined, although false-positive results are not uncommon. IgM titers may be persistently elevated for months. Excitation conduction disorders as initial manifestation of a rheumatic (e.g. systemic lupus erythematosus) or infiltrative disease (amyloidosis) are rare [3].
Clinic and diagnostics
The cause of bradycardia is usually sinus node dysfunction or atrioventricular conduction disturbance (Fig. 2-8). Typical symptoms of bradycardia or asystole are dyspnea, intolerance of performance and, above all, dizziness and even presyncope or syncope. Especially in AVB type 2:1, sudden power intolerance may be accompanied by dyspnea or symptoms of heart failure [4]. In a long AVB I° or AVB II° type Wenckebach, symptoms such as palpitations or pulsations in the area of the jugular veins may occur due to the very long AV conduction time and the consecutive early diastolic atrial contraction.
The AV valves are not yet open during atrial contraction and “atrial plugging” occurs [3]. If the arrhythmias are persistent, a normal 12-lead ECG is sufficient to make the correct diagnosis. If bradycardia occurs paroxysmally, a Holter ECG is necessary. Here, the recording duration should be adapted to the symptom frequency (Tab. 2) . In case of long symptom-free intervals, loop recorder implantation may be helpful for diagnosis. Only rarely is an electrophysiological examination necessary for further clarification, for example, in the presence of a thigh block in the resting ECG and in recurrent syncope of unclear etiology or in st. n. myocardial infarction and clinical suspicion of ventricular tachycardia [3]. If the syncope occurred during physical exertion, ergometry is recommended for clarification. If reflex syncope is clinically suspected, a tilt table examination and carotid pressure test should be performed. Both tests are positive only when a cardioinhibitory response is documented [3].
Pacemaker indication
The European Society of Cardiology (ESC) guidelines on pacing and cardiac resynchronization therapy (CRT) were updated and extensively revised in 2013 (Fig. 9, Tables 3 and 4) [3].
Sinus node disease (sick sinus syndrome, chronotropic incompetence, sinus arrest, SA block) generally has a good prognosis and pacemaker implantation should be performed only to treat documented symptomatic bradycardia or asystole. No reduction in mortality with pacing therapy has been shown [3]. The same is true for tachy-brady syndrome.
In AV block I° and II° type Wenckebach, the prognosis is also good and pacemaker implantation is indicated only if symptoms occur. Because of the unfavorable prognosis of untreated AVB II° type Mobitz or total AV block, there is an indication for pacemaker implantation even in asymptomatic patients.
In addition, patients with heart failure, reduced LV systolic function <35%, and left bundle branch block or intraventricular conduction delay with QRS width >150 ms are indicated for resynchronization therapy (CRT). In the absence of contraindications, CRT is usually combined with an internal defibrillator to protect against sudden cardiac death.
Recurrent cardioinhibitory syncope without prodromes is associated with a high degree of distress, although overall it has a favorable prognosis. After conservative measures have been exhausted, pacemaker implantation may reduce the recurrence rate of syncope in patients 40 years of age and older. This has not been demonstrated in a younger patient population and pacing is generally not recommended [3].
A history of syncope and documentation of asystole >6 seconds also indicate pacing [3].
A rare cause of syncope is alternating right and left bundle branch block, which is a pacing indication regardless of symptoms [3].
Literature:
- Statistics of the Pacemaker and Electrophysiology Working Group of the Swiss Society of Cardiology. www.arrhythmia.ch
- Reynolds D, et al: A leadless intracardiac transcatheter pacing system. N Engl J Med 2016; 374: 533-541.
- Brignole M, et al.: 2013 ESC guidelines on cardiac pacing and resynchronisation therapy: the task force on cardiac pacing and resynchronisation therapy of the European Society of Cardiology (ESC). Developed in collaboration with the European Heart Rhythm Association (EHRA). Europace 2013; 15(8): 1070-1118.
- Barold SS, Herweg B: Second-degree atrioventricular block revisited. Cardiac Pacemakerther Electrophysiol 2012; 23(4): 296-304.
- Nada A, et al: The evaluation and management of drug effects on the cardiac conduction in clinical development. Am Heart J 2013; 165(4): 489-500.
- Narula OS: Cardiac arrhythmias: electrophysiology, diagnosis and management. Baltimore-London: Williams and Wilkins 1979.
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