It was 5 am, the quietest part of the morning. My night shift hadn't been too bad, the wards had been relatively quiet and I even managed to get some well-needed sleep.
That’s when my bleep went off; a nurse, from one of the medical wards on the top floor. A drug chart had expired - a typical house officer request - it needed rewriting. As I began the long walk to the stairs I passed by a side room with a patient I had clerked in the day before: Abigail, a 23 year-old woman who’d been brought in after taking a paracetamol overdose. Paracetamol Poisoning
She seemed in distress and called for help, so I walked into the room. She told me her heart was pounding incredibly fast, that she felt short of breath and was sweaty all over. It had happened all of a sudden; she had just woken up from sleep. She thought she was just anxious about being in a different environment and so hadn’t pressed her buzzer for help. Something about the way she looked made me think this was more than anxiety.
The observation chart at the end of the bed hadn’t been updated since the night before - everything had looked stable then. I took her radial pulse, then retook it as 150 bpm seemed far too fast, but I’d been right the first time. Abigail had pretty severe tachycardia, but why? Cardiovascular Reflexes ◦ Cardiac Action Potentials
I called for a nurse and got no response. The lights on the ward were off and it seemed like no-one was around. It must have been a quiet night for everyone. I managed to find the light switch in the room and then found the switch to turn on the corridor lights. Finally, I heard footsteps coming down the corridor; someone else was awake around here! When he arrived, I asked the nurse to take the blood pressure and then went back to my patient.
She had clammy hands but was warm and well perfused. She had no JVP to speak of and had a cannula in the left antecubital fossa. Her heart sounds were too rapid to interpret any murmurs, her lungs sounded normal and her abdomen was soft and not tender. Jugular Venous Pressure
The nurse reported that her blood pressure was 110/70 mmHg, her O2 sats were 97% and her heart rate was still around 150 bpm. I estimated that her respiratory rate was high at about 22 breaths per minute. Pulmonary embolism came to mind, but you’d expect O2 sats to be lower in that situation. Could anxiety produce such a high heart rate? It seemed unlikely, as she didn't seem particularly anxious. Had she taken something else we didn’t know about? She denied this, vigorously. I took some bloods and asked for an ECG. E C G Basics
That wasn't a sinus rhythm. She had a narrow QRS complex tachycardia and the P waves were either missing, or were inverted and appeared after the S wave complex. That could mean that the atria were being depolarized oddly, such as in AVNRT or AVRT. It didn't look like flutter, fibrillation or atrial tachycardia. In a young woman, my money was on AVNRT. Atrioventricular Reentry Tachycardia ◦ Atrioventricular Nodal Rentrant Tachycardia ◦ Narrow Complex Tachycardia
Realising that the patient needed urgent treatment, I called for help. The medical registrar was busy with the start of the 5 am A&E rush downstairs but would come up in 15-20 minutes. In the meantime she fired a list of advice: “Cardiac monitor, defibrillator pads, big cannula, check for history of asthma. Try vagal manœuvres." Vagal Manoeuvers
I asked the Abigail to blow into a syringe — straining to try and blow the plunger out — didn’t really have much effect. I tried carotid massage, one side then the other, still no change.
I asked the nurse to prepare some adenosine for infusion, and some saline to flush and make sure it got in properly.Adenosine For Supraventricular Tachycardia
Once the patient was attached to the defib and the reg had arrived, we gave the adenosine — 6 mg — and watched the ECG trace — suddenly nothing …… and back to sinus rhythm. Although briefly uncomfortable, Abigail felt better almost immediately.
Abigail told us later that this had happened before once after a night of heavy drinking but that it had gone away on its own after she’d been to the toilet. On her discharge for hospital we referred her to a local cardiology service, “Are there any drugs that I can take to stop this happening again?”