Overview of Overdrive Pacing
Temporary cardiac pacing (TCP) is a method used to manage some types of heart problems. It involves using an outside energy source to send small electric shocks to your heart. This procedure would help speed up your heart if it is beating too slowly, or helps control your heartbeat if it is erratic (unstable heart rhythms). TCP is usually used when heart medications or shock treatment (cardioversion) hasn’t worked.
This special procedure has been used since 1952 by Paul Zoll. He used special type of needles through the chest to give a pulsating electric current to the heart to start beating again. Today, it can be used in a wide range of emergency or critical care situations. The doctors can apply TCP in different ways – through the skin (transcutaneous), through a vein (transvenous), directly on the heart (epicardial), or down through the throat to reach your heart (transesophageal). In this activity, we will focus on temporary cardiac pacing in critical care settings.
Anatomy and Physiology of Overdrive Pacing
The heart sometimes needs help to beat properly, and this is where cardiac pacing comes in. It involves using an external power source to send electrical signals to the body’s heart muscle, which stimulates it to contract and pump blood efficiently. This allows doctors to control the heart’s electrical system.
Normally, the heart’s electrical signals start in a region called the sinoatrial (SA) node, then pass through the atrioventricular (AV) node and other pathways, causing the heart to contract. However, certain diseases can slow down this system, resulting in insufficient heart rate and reduced blood flow. In such cases, the cardiac pacing technique can deliver artificial electrical pulses that take over from the faulty system, inducing the heart to contract faster and increase the blood flow.
On the other hand, certain conditions can make the heart beat too fast. In case of irregular, fast heart beats (also known as tachydysrhythmias), pacing can help by disrupting the abnormal electrical circuit or overriding erratic signals with artificial ones to restore a stable heart rhythm.
There are several methods of initiating cardiac pacing. Temporary transcutaneous pacing (TTCP) uses external pads placed on the skin to send the signals through to the heart. Additionally, temporary transvenous pacing (TTVP) involves an electrode, inserted through a vein into the heart, to deliver the impulses. Epicardial pacing is applied during heart surgery, where the electrodes are placed directly on the heart. Lastly, transesophageal pacing uses an electrode placed in the esophagus or near the stomach, but it’s used less frequently because it can be uncomfortable.
Why do People Need Overdrive Pacing
Temporary cardiac pacing, a way to help control your heartbeat, might be needed if a person is experiencing a slow heartbeat (known as bradycardia) that is causing symptoms and other serious health concerns. You may receive this type of temporary pacing if a permanent one can’t be given right away, isn’t available, or could potentially be too dangerous. This could be due to a severe instability in your blood flow, known as hemodynamic instability.
The most common reason for needing temporary cardiac pacing is feeling symptoms from a slow heart rate due to a blockage in the heart’s AV node, a part of the heart’s electrical system that controls the heart rate. Many different situations can cause your heart to slow down, which may require temporary cardiac pacing. These include a heart attack, imbalances in your body’s minerals (electrolytes), problems caused by medicines you’ve taken, damage to the heart’s own pace-making system during heart surgery or valve repairs, injuries to the heart, infections in the heart, inflammation of the heart (myocarditis), or after a heart transplant.
Temporary cardiac pacing might also be needed for hard-to-treat fast heart rhythms (referred to medically as refractory ventricular tachycardia, electrical storm, or refractory polymorphic ventricular tachycardia). This treatment can also be used as a preventative measure to stop fast heart rhythms (known as tachydysrhythmias like atrial fibrillation and atrial flutter) from occurring after heart surgery.
When a Person Should Avoid Overdrive Pacing
There aren’t any hard and fast rules against temporary cardiac pacing, a procedure that uses a device to help the heart beat at a regular rate. However, there are some situations where it’s best to be careful or avoid it altogether. The main time doctors tend to avoid this is when a person’s heart beats slowly, yet the condition doesn’t severely affect them or cause extreme discomfort.
Medical professionals also tend not to use cardiac pacing when a patient has hypothermia, as it isn’t needed then, or during a long period where the heart is beating slowly and irregularly, as the conditions make the procedure ineffective.
It’s also best to skip this treatment for people with a mechanical tricuspid valve – one of the four main valves in the heart – because introducing a catheter might damage the valve. The same goes for patients who are at a very high risk of bleeding, including those with an acute heart attack who are being treated with blood thinners and platelet blockers.
Equipment used for Overdrive Pacing
Temporary skin-level pacing needs a device that creates electrical pulses (referred to as a pulse generator) and a unit for monitoring heart activity, along with standard shock-delivering pads. These types of equipment are commonly found in most medical environments. The pulse generator must have a function for pacing the heart. Other tools like heart activity sensors, tools for measuring blood pressure (either non-invasive, meaning it doesn’t need to pierce the skin, or invasive), and tools to measure the level of oxygen in the blood are highly recommended as well.
Temporary vein-level pacing involves inserting a wire through a vein, usually by using a 6 French (Fr) diameter sheath or tube, a special pacing wire (known as a catheter), and a pulse generator outside the body. Generally, using ultrasound to guide the placing of the catheter is highly recommended. You also need equipment like a machine that can check electrical signals from different parts of the heart, a heart monitor, tools to measure the body’s blood pressure (either invasive or non-invasive), and a tool to monitor the oxygen levels in the patient’s bloodstream. This process must be carried out in a sterile manner, following medical protocol to keep everything clean and germ-free.
The pacing catheter that is inserted in the vein is usually bipolar, measuring 3 Fr to 5 Fr in diameter and 100 cm length. Usually, there are marks at every 10 cm intervals to assess the depth of insertion. The catheters can vary in flexibility, from semi-floating to rigid. Generally, for emergency circumstances where temporary pacing is required, a semi-floating catheter with a small balloon is used. This balloon is inflated with 1.5 ccs air and needs to be tested before use. The front end of the catheter has two electrodes (devices used to conduct electricity), with the negative one being further out. There are adapters available that allow these electrodes to connect to the pulse generator.
The external pulse generator sends an electric current down the pacing catheter, measured in tiny units of electric current called milliamperes (mA). All generators essentially have the same features, which include control over the electric output and components to sense heart activity. These are shown as dials on the front of the generator. The output control feature allows adjustment of the electrical pulses sent down the wire to help trigger the heart to beat. It lets you control the pacing rate by choosing the speed of the heartbeats. The sensitivity control feature sets a limit for when the pacemaker is triggered to send out a pulse. This setting can be used for either synchronous (triggered by the patient’s heart activity) or asynchronous (providing a fixed heart rate) pacing. In most urgent cases, the sensitivity control is turned down to the lowest setting, allowing for a constant fixed rate heartbeat.
Epicardial pacing, which involves connecting a pacemaker to the outer layer of the heart, typically needs an external pulse generator and surgical pacing electrodes. The location of these electrodes needs to be confirmed with the surgical team.
How is Overdrive Pacing performed
Temporary Transcutaneous Pacing (TTCP)
This method of stabilizing your heart rhythm involves using sticky patches (pacing pads) that send small electric signals to your heart. It can be a bit painful because of the strength of the electrical current. Here’s how it’s done:
1. Depending on the situation, you might get something for pain or relaxation before or right after the pacemaker is turned on.
2. The pads are attached to your chest and back (or sometimes just the front), and then connected to a machine called a pulse generator (you might recognize this as the machine used for defibrillating).
3. Then the machine is set to send pulses at a desired heart rate, usually between 60 to 80 beats per minute (BPM), or 10 to 30 BPM faster than your heart’s current rate.
4. The machine is started with a power level of 70 milliamps (mA), which is then slowly increased until your heart responds (this is called ‘capture’), showing a specific reading on an electrocardiogram (ECG) and signs that your body is getting enough blood flow.
5. Sometimes the machine may show signs of the heart responding, but this doesn’t mean that the heart is actually beating. It’s very important to check to make sure your heart is responding correctly. You can check this by feeling your pulse, using an echocardiogram, or using a device that measures oxygen in your blood.
6. If your heart doesn’t respond correctly even after increasing the power to more than 120 mA, the pads might need to be repositioned.[1][6]
Temporary Transvenous Pacing (TTVP)
This is a more complex method, which involves introducing a thin plastic tube into your vein to reach your heart, and using this to send the pacing signals instead. Your vein will be accessed using a really slender plastic tube (or sheath), usually 6 French units wide. This might sound really small, but it’s just right for the pacing catheter to fit through. The veins typically used for this are the right internal jugular vein and left subclavian veins. The procedure is performed with ultrasound for guidance.
1. First things first, the pacemaker electrodes are connected to the pulse generator.
2. The pacing catheter is then inserted through the access sheath, making sure that the parts of the catheter responsible for sensing and pacing are past the end of the sheath.
3. Once the catheter is correctly placed, the pulse generator is switched on, set to the desired pace and to a starting output.
4. A balloon at the end of the catheter is then inflated and the catheter is pushed forward slowly, while watching a cardiac monitor to check for the correct readings, signs of stabilized heart rate, and improved blood flow.
5. Then, the output is adjusted until the heart doesn’t respond, then increased until it does; this is the ‘threshold’. The starting output should be set higher than this to maintain ‘capture’.
6. Finally, if regulating your normal heart rhythm with the pacemaker is the goal, the pacemaker will be adjusted to ensure it only steps in when your heart isn’t beating at the correct rhythm.
Epicardial Pacing
This method is used for treating issues with the rhythm of your heart if the problem arises or exists within the muscle of your heart.
1. Just like previous methods, the desired parameters depending on the situation are set on the pulse generator.
2. If the goal is demand pacing, the settings are adjusted such that your heart’s signals take over the pacemaker. Then, the pacemaker rate is set. This rate is the backup rate and the pacemaker will deliver an impulse if it does not sense a signal from your heart beating at a higher rate than the backup rate.
3. Then, the pacemaker’s power setting is tweaked and the signs for ‘mechanical capture’ as explained above are evaluated. [2][7]
Possible Complications of Overdrive Pacing
TTCP (Transthoracic cardiac pacing) and TTVP (transvenous ventricular pacing) are two ways to control your heart rate if it’s beating too fast or too slow. Just like with any procedure, there are potential complications with both methods.
With TTCP, some people might experience pain or the method might not work as expected. There’s also a small chance of skin burns. However, a large number of complications are associated with TTVP, many of which are related to the process of accessing the veins in your chest. These complications may involve infection, bleeding, damage to nearby parts of your body, clots in your vein, air bubbles in your blood, or pneumothorax (a condition where air fills the space around your lungs). In rare cases, TTVP can sometimes cause your heart to beat very fast or in an irregular way, a condition known as ventricular tachycardia or ventricular fibrillation.
What Else Should I Know About Overdrive Pacing?
Transcutaneous pacing (TCP) is a medical procedure used to regulate the heartbeat. The careful selection of patients for this procedure is crucial, because while this treatment can be beneficial for some individuals, it might have a higher risk than benefit ratio for others.
This method is typically used when other treatments have not worked – for instance, if various medications or a procedure called cardioversion (to restore normal heart rhythm) haven’t been successful in regulating the heart’s rhythm.
One important consideration in transcutaneous pacing is not to assume that electrical activity in the heart (measured as a QRS complex) automatically translates to the heart’s ventricles contracting as they should. Sometimes, this electrical activity occurs without the related heart muscle contractions. This problem is especially prevalent with transcutaneous pacing due to the chest wall’s resistance and the heart being deeper than the pacing pads.
To ensure that the heart contractions (mechanical capture) are occurring alongside the electrical activity, health professionals need to confirm a matching pulse-rate set by the pacemaker. They can do this using a variety of methods, such as feeling the pulse, using a heart ultrasound (echocardiogram), and pulse oximetry (a non-invasive method to monitor the oxygen saturation in your blood).
Another important factor to be aware of is verifying the heartbeat using the ECG monitor associated with the defibrillator or pulse generator being used, rather than an independent cardiac monitor. The position of the pacemaker’s wire (catheter) is typically confirmed by a chest X-ray or echocardiography. This monitoring should also be frequently checked, especially after movements, other procedures, or if the patient has been repositioned.
