Devices: Difference between revisions

A pacemaker monitors the electrical impulses in the heart. When needed, it sends small electrical impulses to the heart muscle to maintain a normal heart rate.

 

 

A pacemaker rhythm can easily be recognized on the ECG. It shows pacemaker spikes: vertical signals that represent the electrical activity of the pacemaker. Usually these spikes are more visible in unipolar than in bipolar pacing (see below).

[[File:DVA0968.jpg|thumb|VB ECG pacemaker]]

Pacemaker implantation is performed under local anaesthesia in a sterile operating room or catheterization laboratory. Implantation starts with inserting the pacemaker lead(s), most often into the left or right cephalic vein. Fluoroscopy is used to ensure the appropriate location in the atrium or ventricle. Leads are often positioned in the auricle of the right atrium and/or the right ventricular apex.  

{| class="wikitable" border="1"

! Wet van Ohm:

| U = I x R

| U = Voltage

| I = Current

| R = Impedance

==Device measements==

* Stimulation threshold (in mV@ms): The stimulation threshold is the minimum stimulus intensity (in mV) and duration (in ms) necessary to capture the heart.

* Sensitivity (in mV): The degree that the pacing system “sees” or senses signals, controlled by the sensitivity setting which is graduated in mV.

* Battery: Device longevity is estimated based on the remaining battery voltage and battery impedance (and past history of percent pacing in case battery status is checked at follow up visits).

[[File:temp.jpg|thumb|none|VB drempelen]]

{| class="wikitable" border="1"

! I

! II

! III

! IV

! V

| Chamber(s) paced

| O = none

D = dual (A+V)

D = dual (I+T)

'''Explanations of table:'''

'''Dual:''' A pacemaker with dual response to sensing will inhibit a pacemaker output pulse if it senses an intrinsic event in that same chamber, but it will trigger a pacemaker output pulse in the ventricle if it senses an intrinsic event in the atrium (after a programmed atrioventricular interval)

'''Rate modulation:''' In some patients, rate adaptive pacing is programmed “on” to ensure that when patients exercise increases, the pacemaker ensures that the heart rate increases to provide additional cardiac output. There are many ways to sense physiological exercise, including motion sensors and ventilation sensors.

* '''AAI:''' The atria are paced, when the intrinsic atrial rhythm falls below the pacemaker's threshold.  

* '''VVI:''' The ventricles are paced, when the intrinsic ventricular rhythm falls below the pacemaker's threshold.  

* '''VDD:''' The pacemaker senses atrial and ventricular events, but can only pace the ventricle. This type of pacemaker is used in patients with a reliable sinus node, but with an AV-block.  

* '''DDD:''' The pacemaker records both atrial and ventricular rates and can pace either chamber when needed.

* Unipolar: Pacemaker circuit between 1 electrode at the distal end of lead and the pacemaker pulse generator (large circuit ± 40-60 cm).

** Advantage: large pacemaker spikes (easier interpretation pacemaker ECG)

** Disadvantage: extracardiac stimulation (pectoral muscle), sensing of extracardiac signals (such as ventricular depolarisations in the atrial sensing channel (far field R waves) or non-physiological noise)

** Disadvantage: small pacemaker spikes (difficult interpretation pacemaker ECG)

===Follow up===

===Complications===

* Undersensing: An intrinsic depolarization that is present, is not sensed by the pacemaker. This can be due to:

[[File:temp.jpg|thumb|none|VB ECG Undersensing]]

* '''Oversensing:''' The pacemakers senses signals on the marker channel that do not correspond to the ECG pattern. This can be physiologic (e.g. ventricular pulse or myopotentials) or non-physiologic (e.g. lead fracture or if the lead is loose from the pacemaker pulse generator or outside interference such as TENS therapy or surgical diathermy).

[[File:temp.jpg|thumb|none|VB ECG Oversensing]]

** Lead dislodgement

** Cardiac perforation

** Poor connection between lead and pacemaker

** Lead maturation: as the lead matures and becomes surrounded by fibrotic tissue, the threshold of stimulation decreases, which may result in non-capture

** Twiddler’s syndrome: a permanent malfunction of a pacemaker due to the patient's manipulation of the pulse generator

** Electrolyte disturbances: hyperkalemia, acidosis and alkalosis can affect the stimulation threshold

** Myocardial infarction: if a MI occurs near the tip of the head, an increase in stimulation threshold and/or non-capture can occur

** Drug therapy: e.g. flecainide can affect the stimulation threshold

** Battery depletion: if the delivered voltage is significantly reduced, advanced stages of battery depletion may result in non-capture

** Exit block: occurs when the stimulation threshold exceeds the pacemaker’s maximum output

* '''Changes in impedance:''' High lead impedance can be due to an open pacing circuit (e.g. lead is not connected to the pacemaker pulse generator or lead fracture). Low lead impedance can be due to a insulation break, which exposes the wire to body fluids which have a low resistance. Also, fluid/blood in the pacemaker header can decrease the lead impedance.

* '''Pacemaker syndrome:''' Pacemaker syndrome is the presence atrioventricular (AV) dissynchrony occurs after pacemaker implantation, regardless of the pacing mode. It is an iatrogenic disease that causes symptoms of fatigue, lightheadedness and hypotension. Symptoms are caused by the loss of atrial contribution to ventricular filling leading to a combination of backward and forward failure. Also atrial cannon waves can be present. In most cases treatment consists of adding an atrial lead and optimizing AV synchrony.  

* '''Operative failures:''' Implantation related complications are:

** Pneumo/hematothorax (may require drain)

** Cardiac perforation/tamponade (may require drain)

** Pericarditis

** Lead dislodgement

** Infection: pocket infection or lead- or pacemaker pulse generator infection (may require pacemaker extraction)

** Bleeding/hematomas (may require drainage)

* '''Long term complications:''' Long term pacemaker related complications are:

** Erosion of the pulse generator through the skin (requires pacemaker extraction)

** Venous thrombosis (vena cava superior syndrome, deep vein thrombosis, lung embolism)

Nowadays, transvenous ICDs can also deliver pacing therapy if necessary. If a patient does not have an indication for pace-therapy, the pacemaker in the ICD is programmed at ''VVI 40 bpm'' (see above pacemaker programming).

 

Secondary prevention is therapy for patients who have already suffered a cardiac arrest or syncopal/hypotensive ventricular tachycardia. All patients who are resuscitated from VT/VF or who experienced spontaneous hemodynamic non-tolerated sustained VT ''in the absence of a reversible cause'' (e.g. acute myocardial infarction or electrolyte disturbances) have an indication for ICD therapy, regardless of the type of underlying heart disease.

Primary prevention is therapy that is given in order to prevent sudden death in patients who have not yet suffered a life-threatening sustained ventricular arrhythmia, but who are at high risk of such an arrhythmia. ICD therapy is effective in patients with a low left ventricular ejection fraction (LVEF) ≤30% more than one month after myocardial infarction that never had shown any ventricular arrhythmia (MADITT II trial). Additionally ICD therapy appeared to be effective in patients with ischemic or dilated cardiomyopathy and a LVEF of ≤35% and congestive heart failure NYHA class II or III.  

===Implantation===

After implantation, defibrillation testing is done by inducing VT/VF to test the ICD system and determine the defibrillation threshold.

 

* '''Heart signal:''' Real time intracardial electrocardiograms are measured. During follow up, sudden and significant decrease or disappearance of amplitudes and/or slew rates for P and/or R waves can be a sign of lead- or device problems and are further investigated.

* '''Sensing and pacing thresholds:''' During ICD implantation baseline sensing and pacing thresholds are measured. During follow-up the sensing and pacing thresholds will be compared to the chronic baseline. Significant increases or decreases may be indicative for lead- or device problems and are further investigated.  

* '''Lead impedance:''' During ICD implantation baseline lead impedance is measured. During follow-up lead impedance is compared to the chronic baseline. Decreases of pacing impedances may be indicative of insulation failure. Sudden and significant increases in pacing impedance may be indicative of conduction fracture.  

* '''Battery status:''' Battery status is determined during implantation and every follow up visit.

 

 

{| class="wikitable" border="1"

! SVT discriminators:

|  

# waveform morphology (broad vs. small complex or comparison of morphology with template of normal QRS wave)

# onset of arrhytmia (sudden vs. slowly)

# stability of arrhythmia (regular vs. irregular)

# relationship between P- and R-waves (atrial lead required)

|}

* '''ATP:''' ATP refers to the use of pacing stimulation techniques for termination of monomorphic ventricular tachyarrhythmias. Such techniques offer the potential for painless termination of VTs.

===Follow up===

 

===Complications===

 

===Cardiac resynchronisation therapy (CRT)===

In appears that atrio-ventricular and intraventricular conduction delays further aggrevates left ventricular (LV) dysfunction in patients with underlying cardiomyopathies. Notably, left bundle branch block (LBBB) alters the sequence of LV contraction, causing wall segments to contract early or late. Dyssynchrony seems to represent a pathophysiological process that directly depresses ventricular function, causing LV remodelling and congestive heart failure and as a consequence causes a higher risk of morbidity and mortality. Atrio-biventricular pacing (CRT) for patients with symptomatic heart failure and intra- or interventricular conduction disturbances has proved beneficial.  

CRT-P or CRT-D appears to be effective in patients with NYHA function class ''III/IV'' for congestive heart failure, LVEF ≤35%, QRS width ≥ ''120 ms'' (especially LBBB) who are on optimal medical therapy. Patients with NYHA function class IV should be ambulatory (no admissions for heart failure during the last month and a reasonable expectation of survival > 6 months).

Also patients with NYHA function class II, LVEF ≤35%, QRS width ≥ ''150 ms'' (especially LBBB) who are on optimal medical therapy are appropriate patients for CRT-D therapy.

* Right atrial lead

* Right ventricular lead

* Left ventricular lead (positioned in the coronary sinus)

[[File:temp.jpg|thumb|none|Plaatje CRT positie]]

#Vardas Vardas et al. Guidelines for cardiac pacing and cardiac resynchronization therapy. Europace 2007

#Epstein Epstein et al. Guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities. Heart Rhythm 2008

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