In the last issue, I talked about cardiac tests and procedures that involve the coronary arteries. I hope you found the article helpful. This issue continues along the same lines and focuses on tests and procedures involving the heart’s electrical system.

In contrast to the heart’s blood supply system (the coronary arteries) that run on the outside of the heart, the electrical system is just below the surface on the inside of the heart. Let’s be perfectly clear: There are no actual wires on the inside of the heart. The electrical system is made of specialized tissue that has conductive properties. It can conduct current at extremely high speeds that begins in the right upper chamber of the heart.

The electrical system is under the control of the nervous system that can speed up or slow down the heart as needed. The heart’s electrical system starts in specialized cells in the right atrium, called the SA (sinoatrial) node. The signal then travels to both atria and to another group of cells called the AV (atrioventricular) node.

The AV node is the gatekeeper between the atria and the ventricles. It allows only so many impulses to pass into the ventricles, preventing the ventricles from fibrillating, which leads to death. From the AV node, the signal passes to the Bundle of His, which gives rise to the right and left bundle branches, causing the ventricles to contract upon stimulation.

Sometimes the heart’s electrical signals are not sent, are blocked or take an alternative route. A pacemaker is generally required if the SA node doesn’t send out the signal (sinus arrest), sends it out too slowly (sinus bradycardia) or alternatively goes fast and slow (sick sinus syndrome).

As mentioned previously, electrical impulses travel from the atria to the ventricles via the AV node. When the signal does not leave the AV node, this is called heart block, and it occasionally requires a pacemaker. Sometimes the atria and ventricles beat independently; this is known as AV dissociation, and it requires a pacemaker. If the signal is slower in one bundle branch versus the other, you get right or left bundle branch block (delay). This generally does not require a pacemaker unless other situations or symptoms exist.

Disorders of the electrical system are called arrhythmias. There are fast arrhythmias that affect the upper chambers (atria) of the heart called super ventricular tachycardias (SVT). These include atrial flutter, atrial fibrillation, AV nodal reentrant tachycardia (AVNRT) and Wolf-Parkinson White syndrome (WPW). Atrial flutter and fibrillation are electrical rhythms occurring outside the SA node, causing the heart to beat irregular (atrial flutter) or irregularly irregular (A-fib). It may last seconds and occur sporadically (paroxsomal) or be persistent and chronic.

In AVNRT, there are two pathways leading from the atria to the AV node: one fast and one slow. The impulse generally travels down the slow pathway and then up the fast pathway. This sets up a loop or circuit leading to a fast heart rate.

In WPW, an extra pathway or accessory bypass tract exists between the atria and ventricles. Signals may travel in either direction (through the AV node and up the bypass tract or through the bypass tract and down the AV node), causing fast heart rates. The second type is dangerous in that it may lead the ventricles to fibrillate.

Arrhythmias of the ventricles are more severe, as well as life threatening. They include ventricular tachycardia (VT) and ventricular fibrillation (VF). In VT, pathways develop in the ventricles (mostly in areas of damaged muscle), leading to extremely fast heart rates that may cause someone to lose consciousness (syncope) or lead to VF. In VF, these extra circuits beat so irregularly that the heart muscle stops pumping effectively and leads to cardiac arrest.

Tests available for detection of arrhythmias:

• Electrocardiagram (ECG) is a test that records the electrical activity of the heart. Multiple electrodes are placed on the arms, legs and chest, where the heart’s electrical activity is then recorded on paper. The ECG can diagnose new or old heart attacks, measure the effect of BP on the heart and diagnose new abnormalities in electrolytes, to name a few.
• Holter monitor is a continuous recording (usually 24 to 48 hours) of the heart’s activity. The monitor’s main problem is that the patient has to wear it all the time. If no symptoms (palpitations or dizziness) develop, it may record nothing other than a normal rhythm.


• Event monitor is generally my favorite test in the diagnosis of arrhythmias. The monitor is about the size of a pager or credit card and is used to detect rhythms that occur infrequently. If you feel symptoms, simply push a button and send the recording to your doctor.


• Electrophysiology study (EPS)/radio frequency ablation is a test in which electrode catheters (thinly coated, flexible wires) are advanced into veins (via the neck, arms and legs) under fluoroscopy to multiple areas inside the heart, where they can record electrical activity. You cannot feel the catheters moving through your heart or blood vessels. Electrical signals from a programmer can send signals via the catheters inside the heart to induce or bring out these rhythms. These electrodes may terminate the fast rhythms with rapid pacing, or an electrical shock may be given (defibrillation). Catheter ablation is an additional procedure that can be performed during the EP study to destroy an abnormal circuit or extra pathway. A specialized catheter called an ablation catheter, using high-energy frequency waves, makes a small burn similar to a solder gun touching a wire. Complications from this study include bleeding, blood clots, collapsed lung (pneumothorax) and perforation of the heart tissue, stroke and death. All are extremely rare. Occasionally the RF catheter may destroy the normal circuit. A pacemaker would then be required. For certain rhythm disorders, this is actually done on purpose.


• Pacemakers and defibrillators (ICDs). Pacemakers are used to treat slow heart rates. Defibrillators are used to treat and prevent fast heart rates, like VT or VF. All defibrillators now have pacemaker capabilities built into them. A pacemaker or ICD is usually inserted in an operating room or cardiac catheterization lab. Only minor anesthesia or conscious sedation is used, thereby reducing the risks associated with general anesthesia. You are awake, but calm, for most of the procedure. The generator is usually placed in the left or right subclavical area, where a pocket is created under the skin, usually above the muscle, to hold the generator. Leads may be advanced under fluoroscopy from the vein (sublclavian) into different parts of the heart. These leads sense the heart’s electrical activity and carry electrical signals from the generator to stimulate the heart. One new benefit of both devices is that they have rate-adaptive capability. This means the rate of your heartbeat can change depending on your level of activity. If you are running, your heart rate speeds up; if you are sleeping, it slows down. Complications of putting in a device include bleeding, surgical infection at the site or involving the entire pacemaker system, clots or air bubbles in the vein, pneumothorax, cardiac perforation, stroke and death. Again, these complications are rare.

 

Final note: I just got married for the second time to a beautiful lady named Jennifer. I consider myself the luckiest guy on the planet, and I’m distressed that many of my colleagues and peers are heading toward divorce. Doctors have an unusually high rate of divorce. It is, as a friend of mine once called it, a “casualty of war.”

I recently attended a course following the book, “His Needs or Her Needs: Building an Affair-Proof Marriage,” by Willard F. Harley Jr. At the conclusion of the course, which is devoted to reducing the divorce rate by 10 percent, something became very apparent to me. As a physician, I am constantly fine-tuning, practicing and working to become a better cardiologist. A successful marriage requires the same effort. I hope I have learned these skills so I can be a better husband the second time around. I highly recommend these words of insight and this program to my peers and readers.

Salvatore A. Barbaro III, M.D., practices general and interventional cardiology at his private practice located at 19234 Stonehue, San Antonio, Texas, 78258. For more information, please call 210-490-4600.