It is not uncommon in an afternoon to see a woman rushing into the emergency department, visibly distressed, telling you that she feels out of breath and her heart feels as if it’s coming out of her chest. You naturally list some rational diagnoses that would explain her symptoms. She adds that her throat is tightening as well, and you find out that her hands are freezing, to which your suspicion grows even more. A shadow of fear looms as you take out your pulse oximeter and try to measure her heart rate…it reads 177 beats per minute. You know what you need to do to be sure of your diagnosis, you order an ECG. The ECG comes back confirming your suspicions. As an example of Murphy’s law the one you fear the most is going to turn out to be the right one. The diagnosis is Supra-ventricular tachycardia. Or, for the sake of your tongue’s convenience, we call it SVT. So what is SVT, and why is it that I fear it so much?
Your heart has four chambers. Two above and two below. These chambers contract when a signal of electricity passes through them. The signal comes from the atrial palace above, from a rightful king sitting on a throne we call the sinus node. The king sends an order and stops for a fraction of a second; it sends another signal and stops again until your heart beats 72 beats per minute, on average. But sometimes, an envious anarchist declares himself to be the legitimate king and establishes another kingdom, thereby disturbing the monarchy of the heart. Hence, your heart develops an additional pathway that makes the signal continue to excite your heart. So the 72 beats per minute, rises to 140, to 160, and sometimes to even more than 200. The kingdom is in danger. This is SVT, but why do I fear it? That will come later.
Now let’s go back to our patient. After confirming the diagnosis, comes the part when you have to treat it. You tentatively glance at the arsenal of your treatment bag and remember the few tricks to use in a case of SVT. Doubtful, you know none of them would likely work because you have tried them with previous usurpers, but you are desperate and you don’t want to go to the scary drug as your last resort. So gently but persistently, you massage the side of the patient’s neck (this is called carotid massage). There are small sensors embedded in your carotid artery. These sensors seek order and are the control centers when something unusual happens in the heart’s holy land. These sensors can control your heart rate and blood pressure by lowering them. So you try to stimulate them to restart the heart and kill the unrightfully self-anointed king. The usurper remains in place and our first approach has failed, as it always has. Now you will ask the patient to place her finger in her throat in an attempt to throw up.
As strange as it may be, she will agree and starts to gag several times. This is not a preparation for something repulsive; this gag reflex stimulates the vagus nerve, and one of its many duties is controlling your heart rate. This maneuver also fails in restoring stability to our kingdom. Another attempt is made to stimulate the vagus nerve by asking the patient to blow as hard as she can into a syringe, lay down immediately, and raise her legs, but this also fails. At this point, the patient suspects she is being mocked by these maneuvers. Finally, after a series of futile attempts, you go for the last resort you have been trying to avoid this whole time.
You ask the nurse to place a wide-bore cannula in a wide vein in the patient’s arm. Then you ask for the drug. Our protagonist is called Adenosine. What does Adenosine do? In simple terms, it stops the heart for a fraction of a second. If everything goes well, it will cut off the extra pathways, kill the crooked king and restart the heart back to its regular rate. You know this is what the patient needs as you have infused this drug into the veins of tens of patients previously, but you can’t help recalling the scary stories of Adenosine only stopping the heart. We don’t want our rightful king to die, but there have been stories of betrayal and friendly fire. Cautiously, you keep a nurse standing by with the paddles of the defibrillator in case the heart fails to start again. Anyhow, the liquid is poured into the syringe. With it, we need 10 ml of normal saline to flush the Adenosine quickly into the heart. The patient is lying down. You put both syringes into the cannula’s ports, push it as fast as possible, and wait. You observe the monitor and simultaneously the patient’s face. After seconds it begins to work.
Some patients describe the feeling of Adenosine as impending doom, a sensation of death arriving, an emotion never felt before. They feel their entire body and existence are being dragged down into the darkness with no return. Some describe it as the coming of a peaceful death. Others have described it in different terms, but in all of them stands the uneasy feeling of dying or feeling death.
As the drug begins to work, fear seeps into your patient’s face, but she is too preoccupied with the dreadful feeling to see your terrified face. She starts breathing heavily and lets out sounds of terror. Meanwhile, the heart rate begins to drop from 177 to 130, to 110, to 90, to 70, to 65.. and your heart rate rises. You pray that it stops at 65 and doesn’t go further down. You let out a breath of relief as her heart rate stops dropping and stabilizes. You didn’t kill someone this time, either. You both survived. As a routine, you request another ECG and see her heart has gone back to its normal state. The kingdom’s realm has been restored. In the end, She’ll leave while being thankful to you for treating her and you being thankful to her for not dying.
This was a simple tale of the fear and the rush of emotions one has to endure in the emergency room, of discrete nagging of conscience, of the soul-tiring stories that are often not talked about. This was the story of Adenosine.
