Temporary Cardiac pacing is a method where a small electrical current is delivered to the heart to initiate myocardial contractions artificially when the intrinsic stimulation of myocardium is insufficient to maintain hemodynamic stability due to disturbances in the conduction system. A temporary pacemaker is used to treat a bradydysrhythmia or tachydysryhthmia when the condition is short lived or to bridge until a permanent pacemaker is placed. There are various methods of performing temporary cardiac pacing: transvenous pacing, transcutaneous pacing, transesophageal pacing, transthoracic pacing, pacing through pulmonary artery catheter and pacing by epicardial wires. The transvenous pacing is by far the most commonly performed technique for temporary cardiac pacing, particularly in the ICU set up. Transcutaneous pacing is another commonly performed temporary pacing method in the ICU set up particularly during emergency situation when little time is available (for example, during cardiopulmonary resuscitation).
INDICATION OF TEMPORARY CARDIAC PACING
Temporary pacemakers are indicated as a bridging procedure in almost all the conditions where permanent pacemakers are indicated. There are certain other conditions where temporary pacemakers are used alone for brief period till the underlying risk subsides. The various indications for temporary cardiac pacing are:
• Treatment of different types of cardiac conduction abnormality following
acute myocardial infarction
– Complete heart block (CHB)
– Mobitz type II second degree atrioventricular block with anterior myocardial infarction
– Bilateral bundle branch block (BBB) (alternating BBB or RBBB with alternating left anterior hemiblock/left posterior hemiblock) with or without first degree atrioventricular block
– New BBB with transient CHB
– New bifascicular block
– Symptomatic alternating Wenckebach block
– Symptomatic bradycardia (sinus bradycardia or Mobitz type I second degree atrioventricular block with hypotension) not responsive to atropine
• Treatment of drug toxicity resulting in arrhythmias
• Second or third degree atrioventricular block causing hemodynamic instability or syncope at rest
• Asystole not related to acute myocardial infarction (AMI)
• Treatment of intraoperative bradycardia caused by β-blocker use in hemodynamically unstable patients
• Treatment of bradycardia dependent of ventricular tachycardia
• Termination of paroxysmal supraventricular tachycardia (PSVT) or type I atrial flutter by atrial overdrive pacing
• Treatment of atrioventricular junctional pacing following cardiopulmonary bypass by atrial or atrioventricular sequential overdrive pacing
• Long QT syndrome
• Torsade de pointes
• Augmentation of cardiac output postoperatively in low cardiac output condition following cardiac surgeries.
• Pulmonary artery catheter placement and right ventricular endomyocardial biopsy in a patient with pre-existing left bundle branch block (LBBB). These procedures may produce short-lasting right bundle branch block (RBBB), which in these patients may lead to complete heart block
• Patients with bifascicular block with or without type II second-degree atrio ventricular block or a history of unexplained syncope, undergoing general anesthesia
• Cardioversion in the setting of sick sinus syndrome
• During pharmacological treatment with drugs that worsen bradycardia
• New atrioventricular or bundle branch block with acute endocarditis
• Various cardiac surgeries, e.g. aortic surgery, tricuspid valve surgery, ventricular septal defect closure, ostium primum repair
• For neurosurgical procedures involving the brainstem and surgical resection of neck and carotid sinus tumors.
CONTRAINDICATION OF TEMPORARY CARDIAC PACING
There are no absolute contraindications to the use of temporary pacing as a means to control the heart rate. Few relative contraindications do exist for a particular type of temporary pacing, which, however, can be overcome by using different method of temporary pacing.
• Patients with severe hypothermia
• Distortions of vascular anatomy or bleeding disorders are relative contraindications for transvenous pacing
• Cardiac glycoside toxicity, as well as other drug ingestions, can cause myocardial irritability, which increases the risk of ventricular fibrillation during the pacing lead insertion
Presence of tricuspid valve prostheses is a relative contraindication for transvenous pacing
• Atrial pacing is contraindicated in the presence of atrial fibrillation and multifocal atrial tachycardia.
TECHNIQUE AND BASIC PRINCIPLES OF TEMPORARY CARDIAC PACING
In 1952, Paul Zoll first applied temporary pacemaker successfully in two patients with ventricular standstill using a pulsating current applied through two electrodes attached via hypodermic needles to the chest wall.4 Since then, various types of pacemaker models came into use. Technological developments produced endocardial, epicardial and oesophagal approaches to pace the heart in addition to the external pacing. All the approaches, however, use an external pulse generator along with electrode or electrodes, through which the electrical impulse is delivered to the myocardium either internally via endocardium or externally via epicardium.
Different Types of Cardiac Pacing
Transvenous pacing: Transvenous pacing involves intracardiac placement of the pacing wire through central venous access. The preferred route for central venous access is the internal jugular vein followed by subclavian and femoral veins. However, other major veins (e.g. external jugular vein, brachial vein) can also be used. The leads are placed into endocardium of atrium and/or ventricle. The right atrial appendage and right ventricle apex provide the most stable positions for lead placement and, therefore, should be the target. The electrodes are placed under ultrasound or fluoroscopic guidance. For insertion of electrodes, flow-directed catheter can also be attempted using pressure or electrocardiography (ECG) guidance. Temporary transvenous pacing is dependable and well tolerated by patients. Both the atrium and ventricle can be paced in a synchronized way leading to improve cardiac output. However, this procedure needs expertise as in inexperienced hands it could be a time-consuming process and a higher incidence of complications is found.
Transcutaneous pacing: This is by far the simplest and quickest technique where the heart is paced by the application of external pads over the chest wall. The large external pads are typically placed anteriorly (negative electrode or cathode) over the palpable cardiac apex and posteriorly (positive electrode or anode) at the inferior aspect of the scapula. The anode can also be placed at the anterior right chest below the clavicle. Sedation may be required as this procedure is often uncomfortable to the patients. This technique is commonly used in an emergent condition until temporary transvenous pacing can be instituted. Transcutaneous pacing facility is now available on most modern defibrillators. The Advanced Cardiac Life Support (ACLS) guidelines recommend transcutaneous external cardiac pacemakers for symptomatic bradycardia as a temporary measure and as a consideration for treatment of asystole. Use of transcutaneous external cardiac pacemaker may also be of benefit for overdrive pacing in treatment of certain tachycardias.
Pacing through pulmonary artery catheter:
Temporary pacing can be performed using pulmonary artery catheter (PAC) either with integrated atrial and ventricular electrodes or via Paceport through which pacing lead is inserted. In patients with aortic insufficiency or mitral regurgitation where slow heart rate can cause left ventricular dilatation, PAC with atrial and ventricular pacing capabilities can be useful.
• Thermodilution pacing PAC: This multifunctional PAC is integrated with atrial and ventricular electrodes, which produce atrial, ventricular and atrioventricular sequential pacing. The electrodes are attached to the outer surface of the catheter. These pacing PAC can perform all other functions that can be done using standard PAC such as measurement of right heart pressures, pulmonary arterial and pulmonary artery wedge pressures, blood sampling, solution infusion and cardiac output measurements by thermodilution technique. Using pacing PAC eliminates the need for separate insertion of temporary transvenous pacing electrodes. Varying success, relatively high cost as compared with standard PACs and chance of detachment of the electrodes are the disadvantages of these catheters. A bipolar pacing catheter is available for temporary right ventricular endocardial pacing when hemodynamic monitoring is not needed. It has two electrodes, one at the catheter tip and one 1 cm proximal, providing capabilities for bipolar pacing. An additional port is sometimes present to facilitate blood sampling or solution infusion. This probe can also be used for intra-atrial or ventricular ECG monitoring.
• Paceport PAC: This multifunctional five lumen PAC (Fig. 3) is provided with a Paceport (right ventricle port), through which a separate bipolar pacing lead can be inserted to produce stable ventricular pacing whenever necessary. This type of catheters is used when a condition for temporary cardiac Pacing cannot be diagnosed at the time of catheter selection and insertion. The Paceport PAC catheter provides for rapid ventricular pacing along with hemodynamic monitoring when the patients with LBBB develop complete heart block during its insertion. The pacing port can be used for pressure
measurement or fluid infusion when the pacing lead is not inserted. This type of catheters, however, lack the advantages associated with atrial pacing capability. The newer pulmonary artery A-V Paceport catheters possess a sixth lumen to accommodate an atrial pacing lead.
Pacing by epicardial wires: This is a commonly practiced technique for intraoperative and postoperative management of dysrhythmias associated with cardiac surgeries. The epicardial wires are placed during intraoperative period under direct vision. This is a very reliable short-term technique where atrium and/or ventricle can be paced. Development of an inflammatory reaction around the wire and myocardium interface, and failure to sense and capture after few days (typically after 5 days) are the major problems associated with this technique.7
Transthoracic pacing: In this method, a pacing wire or needle is directly introduces to the ventricular wall through the thorax by piercing the thoracic wall. Transcutaneous pacing has replaced this method. This is a useful technique during cardiac arrest, prophylaxis during catheter placement, and as a standby method in case of high risk of bradycardia.
Transesophageal pacing: This is the newest technique available. This relatively noninvasive and well-tolerated technique requires introduction of pacing lead through oropharynx to the esophagus where the electrodes are placed against left atrium. A modified oesophagal stethoscope is used for this purpose. Pacing capture should be confirmed by the presence of peripheral pulse as detected by plethysmogram or invasive hemodynamic monitor. By this type of pacing only asynchronous atrial-only mode pacing is possible. In addition, the higher pacing threshold (8–20 mA) is necessary for successful capture. For successful capture, the pacing output should be set at 2–3 times the pacing threshold. A special generator, that must produce 20–30 mA of current output and a pulse width up to 10–20 milliseconds, is needed. This technique has been shown to be especially useful for diagnostic purposes in pediatric age group.
The transvenous temporary pacemaker is the most commonly done procedure for temporary pacemaking that needs technical skills involving few steps and an adequate set up. Steps for transcutaneous, transthoracic and transesophageal pacemaker insertion are very straightforward and simple to perform, although, the indications may vary for each of these methods. Choice of pacing technique is often influenced by the clinical setting, e.g. flow-guided balloon tipped catheter is less optimal in the setting of cardiac arrest due to no or minimal circulation is available, where transcutaneous pacemaker is indicated as it can be applied quickly and easily just by applying two external chest pads. After cardiac surgery, it is likely to have epicardial electrodes as they can be inserted directly under vision before the chest closure, eliminating the need for transvenous pacing subsequently. Pacing PAC (Swan-Ganz catheter), being less stable, is better avoided in conditions where temporary pacemaker has to be continued for some time and in pacemaker dependent patients. Insertion of pacemaker leads using PAC catheter is similar to insertion of normal PAC catheter using Seldinger technique.
• Components of a temporary pacemaker unit: Pulse generator, leads or wires and electrodes.
– Single chamber: This simple, easy to operate pacemaker is used when only one pacing electrode is available and can sense and stimulate only one chamber (atrium or ventricle) at a time. The pacing modes available with this model are synchronous (AAI, VVI) and asynchronous (AOO, VOO). Single chamber atrial-based pacing can be used in sick sinus syndrome with intact atrioventricular nodal function. There are three dials present for determining pacing rate, pacing threshold/output and sensitivity. In addition, there are buttons for ‘rapid atrial pacing’, which can be used to manage atrial flutter.
– Dual-chamber It can pace both right atrium and right ventricle using two separate pacing leads. The biggest advantage of this type of pacemaker is capability of atrioventricular sequential pacing which is more physiological and maintains better cardiac output. The different temporary pacing modes available are atrial (AOO, AAI), ventricular (VVI, VOO), or dual chamber (DDI, DDD, DOO, or DVI) and rapid atrial pacing (80–800 ppm). In comparison to single chamber pacemaker, dual chamber device is more complicated and needs more expertise in terms of optimizing the device to the patient, and requires more understanding of device timing cycles.
– Sensitivity: Sensing is the ability of the pacemaker to detect natural (intrinsic) depolarization by measuring changes in electrical potential of myocardial cells. Sensitivity is the minimum current at which the pacemaker is able to sense intrinsic rhythms. It is represented numerically in millivolt (mV) on the pacing generator. The greater the number, the less sensitive is the device to intracardiac events. The sensitivity is adjusted to detect appropriate intrinsic electrical signal and at the same time filtering out the unwanted signals. A pacemaker is said to be ‘oversensing’ when it detects electrical signals other than the intended P or R wave, which may inappropriately inhibit pacing leading to underpacing. This happens when the sensitivity value of the pacemaker is kept low. A pacemaker will ‘overpace’, if the sensitivity value is set too high (making it less sensitive) leading to inability to recognize the intrinsic beat, and thus responding inappropriately. To determine the sensing threshold, the pacemaker rate is first set below (by 10 ppm) the endogenous rate if present, the pacing output is set to 0.1 milliampere (mA) and the mode is fixed to AAI, VVI or DDD. Then, the sensitivity number is increased (thereby, making the pacemaker less sensitive) until the sense indicator stops blinking. At this moment, the pacemaker starts pacing asynchronously. Once this is achieved, the sensitivity number is turned down until the sense indicator starts blinking with each intrinsic rhythm. The value at which this occurs is the threshold value. The sensitivity value is usually set at half the threshold value due to the possibility of peri-lead fibrosis over the course leading to reduction of the current transmitted to the pacemaker and also for small electrical signals.
– Capture threshold and pacing output: The capture threshold is the minimum pacing output at which an action potential is generated leading to myocardial contraction. To determine the capture threshold, the pacemaker rate is set above the endogenous rate. Following this, the pacing output is gradually decreased until a QRS complex is not preceded by a pacing spike seen in the ECG. The output at which this occurs is called the capture threshold. Typically, the pacing output is set at twice the capture threshold for safety margin. If the capture threshold is found to be more than 10 mA, then the safety margin is kept low as higher pacing output for long time may lead to myocardial fibrosis at the lead and myocardium interface.
– Pacing rate: The objective of setting a pacing rate is to get the maximum cardiac output. This, however, increases the myocardial oxygen consumption in an already compromised heart. A standard protocol is to set the heart rate around 80–90 per minute unless indicated otherwise.
– Pacing mode: Almost all type of pacing modes, which are present in permanent pacemaker, are also available in temporary pacemaker. The mode is commonly represented by three letters (e.g. VVI, DDD, etc.) according to the NBG codes. The first letter represents the chamber(s) paced. It can be A (Atrium) or V (Ventricle) or D (Dual; both atrium and ventricle). The second letter represents the chamber sensed. It can be A (Atrium) or V (Ventricle) or D (Dual; both atrium and ventricle) or O (None). The third letter represents response to sensing. It can be I (Inhibited; demand mode) or T (Triggered) or D (Dual; both triggered and inhibited) or O (None; asynchronous). For example, VVI pacing mode indicates ventricle is the chamber, which is both paced and sensed, and inhibition is the action when sensed an event. There are two more letters in the nomenclature, which are not frequently used. The fourth letter represents programmability and is either O (None) or R (Rate modulation). The fifth letter represents multisite pacing. This can be A (Atrium) or V (Ventricle) or D (Dual; both atrium and ventricle) or O (None).
• Pacing leads and electrodes
– Temporary transvenous pacing lead: This smooth tipped, atraumatic, bipolar pacing leads are available in various sizes and lengths. The tip of the lead is either straight or curved at different angles. The atrial lead is J-shaped.
– Balloon-tipped: This bipolar temporary pacing lead with balloon is suitable for both recording intracardiac signals and temporary pacing. The usual length of this lead is 105 or 110 cm. The balloon at its tip helps in accurate flow-directed placement. These are stiff with a performed atrial “J” wire with a balloon at the tip to help floating.
– Endocardial screw-in lead: This bipolar lead is available in different lengths: 60, 90, 100, 140, 200 cm. This lead can also be used for intracardial ECG recording. The greatest advantage of this lead is full mobility of the patient without dislocation of the electrode due to firm anchoring of the electrode tip.
– Epicardial wire: This is available in unipolar, bipolar or quadripolar configurations and is available in various lengths.
– Transthoracic patches: This self-adhering, noninvasive stimulation leads are indicated for transcutaneous pacing, ECG monitoring and defibrillation and cardioversion. Modern transcutaneous external pacemakers use long electrical pulse duration (40 milliseconds) and large electrodes (80 cm2).These features reduced the current required for capture as well as patient discomfort.
– Esophageal lead: It is available in both pediatric as well as adult sizes. The number of electrodes at the tip could be 2, 4 or 8. The curved electrodes produce good tissue contact in esophagus. The transesophageal stimulation is pain free.
Temporary transvenous pacemaker insertion involves obtaining central venous access followed by intracardiac placement of the pacing wire. Here, the steps for insertion of transvenous pacemaker are described.
PREPARATION OF TEMPORARY CARDIAC PACING
Standard aseptic precautions are to be taken. Before initiating the procedure ensure defibrillator and resuscitation equipment are present along with monitor capable of monitoring vitals parameters such as ECG, pulse oximetry, invasive or noninvasive blood pressure.
PROCEDURE OF TEMPORARY CARDIAC PACING
• Position of the patient: supine.
• The skin at the site of central venous access should be infiltrated with local anesthetic (lignocaine).
• Standard technique for central venous catheter placement should be followed. Seldinger’s technique is used for vascular access. 6 or 7 Fr size sheath is inserted through femoral vein or internal jugular vein or subclavian vein.
• Ensure the electrode tip is J-shaped (for correct positioning in the heart). Balloon catheters usually have this curvature.
• The electrode is advanced under ultrasound or fluoroscopic guidance.
• The electrode should be advanced in such a way that the tip is directed toward the free wall of right atrium.
• Pass the wire with the help of rotation movement between thumb and index finger through the tricuspid valve to position it along the apex of the right ventricle.
• If difficulties are encountered during positioning of the electrode tip at right ventricle apex, then slide the wire into the right ventricle outflow tract and pull the wire backward to push it again toward the apex with the tip is at a downward angle.
• If unable to capture satisfactorily, then pull back the pacing catheter to right atrium and start over.
• Inconsistent ventricular capture needs fluoroscopy to reveal tip direction: correct it by directing the tip posteriorly or toward left shoulder. Lateral view is helpful along with AP view to see the proper position of lead tip.
• Pacemaker setting: Set the ventricular rate to 10/minute above patient’s own ventricular rate or 70/minute. Start with pulse of 5 V and once the capture is established (spikes followed by QRS), gradually drop the voltage until capture is lost (usually at 0.7–1.0 V). Once the pacing threshold is determined, the pacemaker is set to deliver a pulse of at least twice the threshold. Normally, the sensitivity is set to 1–2 mV so that intrinsic ventricular depolarization can be sensed by lead and no current/spike will be generated from pulse generator. Output parameters of temporary pulse generator of some manufacturer are in ampere instead of voltage. So keep the output at 5 mA or 5 V even the threshold is 0.5 or 1 V. Because the temporary pacing lead is not fixed and position may get changed on movement of patient. So, this can provide extra safety and prevent noncapture. Unlike permanent pacing, we are not bothered about battery life (high output voltage = less battery life)
as it can be replaced as and when required. After the procedure and lead placement, ask the patient to take deep breath and cough to see any capture loss. Lastly, check for diaphragmatic pacing at 10 V output. In both the cases, minimal change of pacing lead tip is required to get consistent capture without diaphragmatic pacing.
• If neither spikes nor output is seen, then check the pacemaker connection along with the normal functionality of the pacing generator. If spikes are seen without any output, then check the position of the pacing wire and reposition it if necessary.
• Fix the wire to the skin by suturing close to the point of insertion once the position of electrode is confirmed with satisfactory capture and output. The area must be covered with antiseptic dressing
Some important points to be remembered:
• Continuous ECG monitoring is recommended for endocardial lead placement
• Fluoroscopy is desirable but not necessary
• Site of pacing lead insertion: Preferred sites are right internal jugular vein or subclavian when it is done as a bedside procedure in ICU, and right femoral vein when it is done as a catheterization laboratory procedure under fluoroscopy.
POST-PROCEDURE CARE OF TEMPORARY CARDIAC PACING
• Patient is advised to keep the lower limb immobilized and not to sit if temporary pacemaker lead insertion was done through groin (e.g. right leg for right groin access).
• At least one ECG after placement (Fig. 9) should be done. QRS complex should appear like LBBB morphology with leads placed at the apex of right ventricle.
• Immediate chest X-ray to ensure lead placement and to rule out pneumothorax.
• Daily threshold check to ensure proper capture and sensing.
• Separate IV access if drugs need to be administered in central line.
• Daily physical examination should be done to rule out pericardial rub (perforation), asymmetrical breath sounds (pneumothorax), hypotension, jugular venous distension (tamponade/pacing problem), fever (infection).
• Daily dressing change with antibiotic ointment.
• Battery status of the pulse generator is very important. Pacemaker-dependent patients who are not on cardiac monitor may die unattended if battery is exhausted and not replaced timely. Usually fully-dependent patient needs replacement of battery at around 48 hours. Some of the pulse generator shows light signal when battery is at low level and indicates replacement is urgent.
• On fully dependent patient, the change of battery should be very quick or else, attach another pulse generator with full battery and start at a rate of 6is beat per minute at 5–7 mAmp or volt output with a sensitivity of 1.5 mV. The connector pins of the leads are to be immediately removed from old pulse generator and reattached to the new one. A transcutaneous pacing may be required if delay in change of battery is anticipated.
• If there is no contraindication, injection Heparin 5000 IU SC twice daily is given to prevent deep vein thrombosis (DVT) particularly when femoral venous route is chosen. If permanent pacing is required, discontinue heparin 12 hours prior to the procedure.
COMPLICATION OF TEMPORARY CARDIAC PACING
• Failure to capture is a common problem, which can be solved either by increasing the pacing output or by repositioning (if the pacing output requires more than 10 milliamps) the leads.
• Failure to pace happens when the pacemaker fails to deliver a stimulus which is manifested by absence of pacemaker spikes on the ECG. This can happen due to oversensing, pacing lead problems, battery or component failure and electromagnetic interference. Among these, oversensing is most frequently encountered. Oversensing occurs due to inappropriate sensing of electrical signals (may or may not be seen on the ECG), that inhibits the pacemaker from pacing.
• Dislodgment of pacing wires is another frequently encountered problem. Knotting of lead wire may also happen.
• Ventricular arrhythmias particularly after post-AMI temporary pacemaker insertion, which may occasionally require removal of the lead or repositioning. These arrhythmias, however, subside when manipulation of the lead has ceased.
• Development of septicemia (most frequently by Staphylococcus epidermidis) occurs when the pacing wire is left in situ for more than 48 hours, which may require treatment with antibiotics. Strict asepsis should be maintained when the leads are placed in situ. Signs of early infection require prompt intervention.
• Thromboembolism may occur in patients susceptible to deep venous thrombosis. Avoidance of femoral route along with DVT prophylaxis should be considered.
• Pneumothorax and/or hemothorax during vascular (subclavian) access for transvenous pacing.
• Transcutaneous pacing is painful, also the ventricular capture is often erratic in this method.
• Cardiac perforation (of right ventricular wall) can be produced by the pacing leads, which may rarely produce cardiac tamponade. Increase in pacing threshold and occasional pericarditis pain are the manifestations. Withdrawing the lead and repositioning it may solve the problem. Cardiac tamponade needs urgent appropriate management.
• Local trauma and hematoma formation.