Essay: Permanent Pacemaker

The normal, healthy heart has its own pacemaker that regulates the rate that the heart beats. However, some hearts don’t beat regularly. For such hearts pacemaker is the ultimate solution for their problem. A pacemaker is a small device that sends electrical impulses to the heart muscle to maintain a suitable heart rate and rhythm. A pacemaker may also be used to treat fainting spells (syncope), congestive heart failure, and hypertrophic cardiomyopathy. It is a small box surgically implanted in the chest cavity and has electrodes that are in direct contact with the heart. First developed in the 1950s, the pacemaker has undergone various design changes and has found new applications since its invention. Today, pacemakers are widely used, implanted in tens of thousands of patients annually.
Components of Pacemaker
A permanent pacemaker has three main components:
1. A pulse generator having sealed lithium battery and an electronic circuitry package.
2. One or more wires (also called leads). Leads are insulated flexible wires that conduct electrical signals to the heart from the pulse generator. The leads also relay signals from the heart to the pulse generator. One end of the lead is attached to the pulse generator and the electrode end of the lead is positioned in the atrium (the upper chamber of the heart) or in the right ventricle (the lower chamber of the heart). In the case of a biventricular pacemaker, leads are placed in both ventricles.
3. Electrodes, which are found on each lead.
Pacemakers are designed to detect when the heart’s natural rate falls below the rate that has been programmed into the pacemaker’s circuitry.
Pacemaker leads may be placed in the right atrium, right ventricle, or placed to pace both ventricles, depending on the condition requiring the pacemaker to be inserted. An atrial arrhythmia (an arrhythmia caused by a dysfunction of the sinus node or the development of another atrial pacemaker within the heart tissue that takes over the function of the sinus node) may be treated with an atrial permanent pacemaker whose lead wire is located in the atrium.
When the ventricles are not stimulated normally by the sinus node or another natural atrial pacemaker site, a ventricular pacemaker whose lead wire is located in the ventricle is placed/used. It is possible to have both atrial and ventricular arrhythmias, and there are pacemakers who have lead wires positioned in both the atrium and the ventricle.
Types of Pacemaker
Generally the Permanent Pace makers have three types which are as under
1. Pacemakers that pace either the right atrium or the right ventricle are called “single-chamber” pacemakers.
2. Pacemakers that pace both the right atrium and right ventricle of the heart and require two pacing leads are called “dual-chamber” pacemakers.
3. Pacemakers that pace the right atrium and right and left ventricles are called “biventricular” pacemakers.
Top Pacemaker Manufacturers
Some of the top Pacemaker manufacturers are asunder
‘ Medtronic, Inc., (U.S.A.)
‘ Pacesetter, Inc., from 1995 a St. Jude Medical Company
‘ Biotronik (Deutschland)
‘ Cardiac Control Systems, Inc., (U.S.A.)
‘ Cardiac Pacemakers, Inc., (U.S.A.)
‘ C C C (Uruguay)
‘ Cordis, Inc.
‘ ELA Medical, Inc, (U.S.A.)
‘ Elema (Sverige), later Siemens-Elema AB, and Pacesetter AB, a St. Jude Medical Company.
‘ Guidant (Minnesota, U.S.A. – Puerto Rico)
‘ Intermedics
‘ Siemens-Elema (Sverige), from 1996 Pacesetter AB, a St. Jude Medical Company.
‘ Sulzer Intermedics Inc.
‘ Telectronics, Inc.
Complications related to Pacemaker
Sometimes pacemakers may cause unwanted complications during and after implantation. Complications related with the implantation process are rare, but include bleeding, infection, or collapsed lung. In general, each of these problems can be treated quite successfully. Though rare, pacemaker problems can occur long after the implantation procedure. These “late” complications include generator malfunction, and lead failure (less rare). Most of these complications are uncommon, and can be prevented by simple manoeuvres. Nonetheless, there are some complications related to pacemaker system disfunctions which may cause life-threatening complications
Complications related to the Leads
Several lead-related complications deserve attention, including lead dislodgement, pneumothorax, loose connector pin, conductor coil (lead) fracture, and insulation break
1. Lead dislodgement
Leads sometimes displaces from the original implant site in the first few days to few weeks following the implantation.
2. Pneumothorax, hemothorax, and air embolism
This complication occurs uncommonly and is directly related to operator experience, the difficulty of the subclavian vein puncture, and is almost eliminated using the cephalic cut down technique.
3. Lead perforation
Myocardial perforation during lead placement is an uncommon but potentially serious complication. The definition of a subacute and delayed myocardial perforation is normal X-ray and electrical parameters (R-wave sensing, pacing threshold, impedance) 24 hours after implantation without clinical signs of perforation and the diagnosis of lead perforation by Xray, echocardiography, or computed tomography 5 days to 1 month (subacute) or ‘ 1 month (delayed) after implantation
4. Extracardiac stimulation
Extracardiac stimulation usually involves the diaphragm or pectoral or intercostal muscles. Diaphragmatic stimulation may be caused by direct stimulation of the diaphragm (usually stimulation of the left hemidiaphragm) or stimulation of the phrenic nerve (usually stimulation of the right hemidiaphragm). Pectoral stimulation may be due to incorrect orientation of the pacemaker with its active surface in contrast with the muscle or a current leak from a lead insulation failure or exposed connector.
5. Venous thrombosis and superior vena cava syndrome (SVCS)
Venous thrombosis occurs early or late after pacemaker implantation in 30% to 50% of patients and may remain asymptomatic because of the growth of venous collaterals
6. Twiddler syndrome
Change from the original position of implantation of pacemaker leads due to twisting of the box on part of the patient is called Twiddler’s syndrome
7. Post pacemaker implant pericarditis
Pericarditis is an uncommon but potentially serious complication following a pacing system implantation. Pericarditis has been reported as a complication of pacemaker implantation associated with the use of active- and passive-fixation leads (Greene et al., 1994). It appeared to occur notably more often when active-fixation atrial leads were used, affecting 5% of implants in this study.
Pocket-related complications
1. Pocket hematoma
2. Wound pain
3. Skin erosion
4. Allergic reactions to the pacemaker component
5. Device-related infections
Leadless/Wireless Pace Maker
Traditional pacemakers that control heart rhythm are safe and effective, but when issues arise, they are mainly related to the wires that connect them to the heart muscle. There is a new breakthrough in field of medical science that is Wireless pacemakers .They are designed to avoid these problems. Because wireless pacemakers have no leads and are not implanted under the skin, they avoid lead-related complications altogether. A leadless pacemaker provides the opportunity of bypassing these complications, but requires a catheter-based delivery system and a means of retrieval at the end of the device’s life, as well as a way of relocating to achieve satisfactory pacing thresholds and R waves, a communication system and low peak energy requirements
Manufacturing Companies
Some of the following companies have disclosed public information about their developments which are as under
‘ Medtronic
‘ Nanostim
‘ EBR System
These companies have manufactured the leadless pace maker in different size and some of them are still on animal testing
Basic Structure
The simplest method of delivery of an endocardial leadless pacemaker is via an intravenous catheter. The largest catheter that can practically be introduced has an internal diameter of 20 Fr (6.66 mm). Therefore, the packaging of the pacemaker has to fit within a 6.66 mm diameter. Also, it should not be longer than a few tens of millimeters in order to follow the curves of the introductory veins. It is preferred to limit its length to 20 or even 10 mm to minimize its invasiveness in the cardiac chamber .The leadless pacemaker size is a cylinder of 6 mm in diameter by 10 or 15 mm in length. The mass is around 2 g and the volume is 0.8 cc
Battery
The energy source is the lithium battery. To be exact lithium silver vanadium oxide is used chemical source for lithium batteries. The longevity of the wireless pace maker is 7 to 12 years which depends of circumstances .It output is 1.5-2 V
Electrodes
The main purpose of electrodes in pacemaker is to send the signals from heart to device and vice versa. It should contain minimum two electrodes .New research in electrodes with respect to leadless pacemaker’s show that 3 electrodes could also be used. The first electrode configures to send electrical pacing energy whereas a second electrode configured to sense intrinsic electrical cardiac activity and a third electrode configurable to both send electrical pacing energy and sense intrinsic electrical cardiac activity. The first and third electrodes are used for delivering electrical pacing energy and the second and third electrodes are used to sense intrinsic electrical cardiac activity
Implantation method
The implantation process is quite simple and less time consuming as compared to the implantation process of conventional pacemaker. This device is delivered via the femoral vein percutaneously by using delivery catheter systems. The venotomy site is upsized to accept the catheter. The pacemaker is carefully inserted in the catheter.r A right ventriculogram is favorable to delineate the right ventricular apical/lower septal anatomy. The pacemaker is delivered across the tricuspid valve with use of a deflectable/steerable delivery catheter.It is than fixed to the heart. Whole delivery process from vein in the leg to the heart is less time consuming .As the procedure is minimal, the patient can be discharged the same day of the surgery
Fixation on heart
Currently there are two methods by which leadless pacemakers attached to the heart which are as under
‘ Radial method
‘ Helix method
Helix Method
It is fixed to the heart via a helix which is very similar to what is used today with conventional pacemaker leads. That helix is the key because it is part of the overall system that enables the device to be retrievable and to be potentially retrievable over the entire lifetime of the device. The helix hold the device in place and provide great stability. It is also designed to be easily disengaged without causing trauma to the cardiac tissue if the device needs to be repositioned
Radial Method
This method for anchoring the pacemaker to the wall of the heart is inspired by the head of a tapeworm. Tapeworms use many small teeth to attach themselves to the wall of the intestine. One tapeworm species has all of the teeth angled in the same direction allowing it to disengage by moving its head in the opposite direction. The teeth simply slide out of their holes upon rotation in the opposite direction. The pace maker contains a number of small wire tines which protrude from the header of the device and curve in the tangential direction relative to the diameter of the device. The number of tines is variable, but preferably as few as two tines (or free end portions) is adequate and as many as 12 tines (or free end portions) is possible depending on device specifications like weight, wire diameter, and wire material. The tines connect with the heart tissue by clock-wise rotation of the device during implantation. The tines release from the heart tissue by anti clockwise rotation. If the tines are unsuccessful to disengage from the heart tissues due to rotation, the device can be removed from the heart by sufficient force at which the tines will deform to slide out of the heart tissue without causing significant injury.
Advantages Of Leadless Pacemaker
1. Reduced surgery time
2. Longer device life as compared to conventional device
3. Less complication due to device
4. Aesthetically more appealing as there is not surgery mark on the body
5. Less infection and complication risk after implantation
6. Same day discharged from the hospital
Limitations
One of the major drawbacks of this device is that this device replaces only single chamber conventional pacemaker. To gain widespread acceptance by clinicians, it would be highly desired for these devices to have dual chamber pacing/sensing capability. It is still on its way for FDA approval
Clinical Human Trails
It has successfully completed the human trials.St. Jude Medical Nanotism leadless pacemaker was implanted in patients. It was planted in 33 patients having average age of 77 (-8,+8) in which 22 patients were male. The overall success rate was 94%. After 3 months of follow-up, the pacing performance measures like sensing, impedance and pacing threshold either improved or were stably within the accepted range.
Future Prospects
1. As it is not appropriate for patients requiring dual-chamber sensing and pacing. Further development can be done to make it dual-chamber (multi-site) pacing .
2. Dimensions can be reduced
3. Battery life can be increased and source can be changed
4. New Fixation method can be developed
5. Additional features can be added