Cardiac Pacemakers

Cardiac pacemaker implant or pacing is used to treat bradyarrhythmias and symptoms like syncope.

sinus bradycardia ecg

Sinus Bradycardia

A bradyarrhythmia represents any sort of rhythm or conduction disorder of the heart, which has the consequence of a low heart rate. In a clinical plan bradyarrhythmias may be manifested by symptoms such as dizziness, decreased exercise tolerance, tiredness, and syncope. Syncope is a temporary loss, a short-term of consciousness of cardiac cause, vascular, neurological. There is no effective medical treatment for bradyarrhythmias of cardiovascular syncope cause; the only effective therapy is the implant of pacemaker.

cardiac pacemakerAbsolute indications for pacemaker implantation include the following pathologies: sinus node dysfunction, atrioventricular block complete, symptomatic sinus bradycardia, sinus node dysfunction accompanied by atrial fibrillation, chronotropic incompetence, long QT syndrome, and sino-carotid hyperreflexia. There are relative indications for pacing and updated guidelines that recommend different classes of indications in cardiac pathology. It is, however, important to note that the indications for the cardiac pacemaker implant must be made ​​by the attending physician, individualized for each patient taking into account the current guidelines, but also by the presence of other symptoms of the patient and the additional diseases. Contraindications for the implant of the pacemaker have patients with localized bacterial infection at the level of the implant site or systemic bacterial infection, bleeding disorders or anticoagulant therapy efficient (relative contraindication – will stop anticoagulation therapy required during implant).

dual chamber pacemakerPacemaker is an implanted battery miniaturized at the subcutaneous pocket level in the left clavicle usually, and through one or more wells of electrical stimulation impulses at the heart level.  A pacemaker has the following components:

  • Pulse generator – contains active circuitry of pacing and sensing. Depending on the case they can detected heart rate and modulate the activity of stimulation.

  • Battery – usually with a lifespan between 7 and 12 years.

  • Wells – conduct the electrically from pulse of the generator in the top of the well electrode is located intra-cardiac and then to the atrial or ventricular myocardial leading to contraction. Wells can be bipolar, when both electrodes are on the path of the probe at a short distance from each other, or when one of unipolar electrode are on the top of the well and the other is in the other it is represented by the pulse generator box.

pacemaker componentsPacemakers are coded by letters; each letter has a specific meaning:

  • First letter indicates the cardiac cavity in which is achieved by stimulating the activity (pacing) and may be V in order for the ventricle, A for the atrium or D (dual) for both cavities.

  • The second letter indicates the cavity is made by sensing the function that notifies the spontaneous activity of the heart pacemaker. For example the letter V stands for ventricular sensing.

  • The third letter represents the answer mode of the pacemaker as a following of the referral intrinsic cardiac activity for example I for inhibiting or T for the triggering.

  • The fourth letter indicates whether the pacemaker has the ability to adjust the frequency of the heating circuit physical activity of the patient. It uses the letter R (from the response rate).

  • Fifth letter can define the anti-tachycardia pacing activity, if this function exists.

For example a pacemaker classified VVIR performs the following functions: Detects ventricular activity of the heart, makes all pacing at the ventricular level, it is inhibited by the spontaneous ventricle activity and the function is based on heart rate adaptation during exercise.

Pacemakers can be for temporary use (in emergencies – acute bradycardia with secure chances of remission, or waiting period till it’s performed the final pacing) or permanent, implantable. In the case of a temporary pacemaker, is implanted intra-cardiac stimulation well, by vascular puncture (usually the jugular vein) and pacemaker battery is external, attached to the wells; it must be maintained besides the patients body and less as possible mobilized.

Cardiac pacemaker implant is performed by interventional cardiologists in the electrophysiology laboratory. The most common pacemaker is implanted in a subcutaneous pocket at left subclavian on or under the pectoral muscle. For example, this technique involves the following steps: left subclavian vein is punctured or is discovered cephalic vein (related to the subclavian vein), it is inserted the well or wells of stimulation by endovenous intra-cardiac wedge. Stimulation wells can be with passive fixation at the endocardial level, or with active fixation, by screwing through a respective cavity endomyocardial level. Subsequently adjacent the place of venipuncture is created a subcutaneous pocket where the pacemaker is placed, the incision sutured and it is applied a compression bandage.  This procedure is performed under local anesthesia (patient is asleep) and using fluoroscopy, an imaging technique that uses X-rays and allows real-time visualization of the heart, as the wells stimulations are inserted and pacemaker placed. Implantation technique varies depending on the operator, by anatomy of each patient, and other technical factors. For example, the pacemaker can be placed in the abdomen, or stimulation wells can be fixed to the surface of the epicardium (outer skins of the heart) and not intra-cardiac.

Choosing the type of cardiac pacemaker is dictated by the pathologist who performed the implant. Mostly pacemakers are single or dual-chamber (with one or two probes), but there are triple chamber pacemakers used in the cardiac resynchronization therapy. The most usage of pacemakers types are:

  • VVI – the easiest way of stimulating unicameral at the right ventricle level. This type of incentive does not provide synchronous activity of the atria with the ventricles, and neither with the left ventricle with the right one and creates the risk of occurrence of the pacemaker syndrome and atrial fibrillation. Basically VVI mode should be recommended in patients with chronic atrial fibrillation and possibly don’t have physical activity or exhibit intermittent atrioventricular block. For all other is recommended to use VVIR mode with adaptation of the heart rate during exercise.

  • AAI – is a type of pacing on the atrial level, being recommended in patients with sinus bradycardia or sinoatrial block, in which atrioventricular conduction function is preserved.

  • This type of pacemaker uses a single well on which two electrodes are situated at the level of sensing atrial function, and ventricular sensing and pacing with the function of. Can be used for patients with heart block but normal sinus node function. It has the advantages of keeping atrioventricular synchronism and allows frequency adaptation to exercise.

  • DDD – has a sensing and pacing function dual / bicameral, and for patients with severe chronotropic (heart rate does not increase enough effort) is used DDDR.

Pacemakers have the option to be programmed and interrogated (checked) using programmers’ specific for each manufacturer. They allow changing the mode of stimulation and detection, parameters change of the pacemaker, interrogation of the time of life (battery validity). If the query indicates pacemaker for life is exhausted it is required reoperation for the battery replacement (usually keeps the stimulation well or wells placed intra-cardiac, and it is just replaced the battery from the pacemaker pocket subcutaneously).

Cardiac pacemaker bearing patient must consider some rules of medical conduct, but also related to daily activity to ensure proper functioning of the pacemaker:

  • The need for regular medical checks: at a week for the suture removal wires from the pacemaker pocket, at a month for crossing the pacemaker on a more economical operating mode,  at 3 months, and then from 6 to 6  months for the pacemaker interrogation.

  • Avoidance of overloading the muscle groups located in the vicinity of the pacemaker lodge (risk of opening a subcutaneous pocket and externalization pacemaker battery).

  • Knowing and avoiding possible interference which can have various pacemaker electromagnetic fields existing in the atmosphere everyday: from stations with high power transceiver to electrophysiology or electro surgical equipment to household appliances that cause electromagnetic fields. Air travel is permitted, the use of mobile phones, passing through airport security devices, using microwaves. These specifications differ depending on the type of device used, and are usually listed in the instruction manual of each pacemaker.

  • For each patient implanted it is needed for a book of pacemaker bearer,  which will specific the name of the cardiologist who performed the procedure, type of apparatus used, the date the procedure was performed, and the indication for pacemaker implantation was performed. This book becomes a kind of “medical ID” of the patient, which then will present at each examination.

Cardiac pacemaker bearers have contraindication in performing the radiological investigations called nuclear magnetic resonance (MRI). However, this is not an absolute contraindication, and like any other medical procedure, should be considered risk-benefit ratio. Since 2011 there are implantable pacing devices that enable safely this investigation – MRI safe pacemakers.

Permanent complications of pacing may be related to:

1. Time of implant and postoperative course:

  • Pneumothorax: by lung damage and accumulation of air in the pleural space. Depending on the severity may require only simple medical supervision, or by needle aspiration, the placement of a chest drainage tube.

  • Hematoma: accumulation of blood at the subcutaneous pocket level requires medical supervision and sometimes drainage.

  • the exteriorization of the pacemaker out-of-pocket the subcutaneous by loosening the suture thread it is a rare complication, requires a change of the pacemaker batteries and systemic administration of antibiotics.

  • Venous thrombosis associated with the implant: it shows as a unilateral swelling of the arm and requires an arm elevation and anticoagulant therapy.

  • Deploying probes: usually occurs in the second day post implant, and can be diagnosed on chest radiography; represents a risk of malignant arrhythmias.

  • Postoperative infection at the subcutaneous pocket level, endocarditis (incidence of these infections has decreased much by using pre-and postoperative antibiotic therapy).

2. Pacemaker malfunctions:

  • sensing deficiency: lack of sensing spontaneous cardiac activity;

  • pacing deficiency: lack of atrial or ventricular response;

  • erratic pacing: irregular or faster than normal;

  • The pacemaker syndrome: usually occurs in patients with single-chamber cardiac pacemaker implant at the right ventricle level, or in patients with bicameral stimulation where the parameters are not properly set for stimulation. Is due for appearance in a desynchronization between the ventricular fibrillation and contraction. Syndrome may be asymptomatic or the patient may present symptoms such as: pulsation in the neck, dizziness, syncope, tachycardia, hypotension, peripheral edema. There is no medical treatment, but by correcting the atrioventricular synchrony syndrome (the unicameral stimulate is getting an upgraded to a bicameral pacemaker, or are modified stimulation parameters, detection).

  • Twiddle’s syndrome: is due to excessive manipulation by the patient, pacemaker at the subcutaneous pocket level that resulted in displacement well stimulation, well fracture, and stimulus erroneous. He has a rare incidence.

Important to remember, patients’ cardiac pacemaker bearers have no contraindication regarding cardio-pulmonary resuscitation or cardiac defibrillation.

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1 Response

  1. March 15, 2015

    […] use of fenfluramine-phentermine, systemic lupus erythematosus. A rare cause of regurgitation is the pacemakers and implantable defibrillators whose probe passes from the right atrium to the right ventricle […]

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