Approach to tachycardia: Clinical sciences

Tachycardia refers to a heart rate above 100 beats per minute, or bpm for short. Once identified, a 12-lead ECG can be used to determine if the tachycardia has a regular or irregular rhythm, and if the QRS complex is narrow or wide. Further examination of the ECG can reveal details that help identify which type of tachycardia is present.

Here’s a high-yield fact! The typical definition of a normal heart rate is between 60 and 100 bpm. However, although tachycardia is technically considered to be above 100 bpm, the SIRS criteria consider tachycardia to be above 90 bpm.

Now, if a patient presents with signs or symptoms of tachycardia, first perform an ABCDE assessment to determine if they are unstable or stable.

If they’re unstable and a pulse is present, then follow the ACLS guidelines for Tachycardia with a Pulse.

Next, stabilize their airway, breathing and circulation. Provide supplemental oxygen, if hypoxemic, to maintain oxygen saturation above 90%. Next, obtain IV access and put your patient on continuous vital sign monitoring including blood pressure, heart rate, and pulse oximetry.

Then assess for signs and symptoms of unstable tachycardia, including heart rate above 150 bpm, hypotension, altered mental status, signs of shock, ischemic chest pain, or acute heart failure.

If your patient has unstable tachycardia, perform immediate synchronized cardioversion.

Now let's go back to the ABCDE assessment and discuss stable patients.

First, perform a focused history and physical examination. Individuals with tachycardia may report symptoms like palpitations, exercise intolerance, lightheadedness, or even syncope. Additionally, physical exam might reveal a rapid heart rate, and if it’s over 100 beats per minute, you can diagnose stable tachycardia.

Next, obtain a 12-lead ECG and assess the heart rhythm by evaluating the consistency of the intervals from one R wave to the next, which is the R to R interval. If the R to R interval is the same from beat to beat, this means that you’re dealing with a regular rhythm.

Let’s deal with tachycardia with a regular rhythm. First, assess the QRS duration, which corresponds to the width of the QRS complex. If the QRS complex is narrow, meaning under 120 milliseconds, there’s a narrow complex tachycardia. In other words, the pacing originates above the ventricles, which suggest you are dealing with supraventricular tachycardia or SVT.

Next, assess the atrial activity on the ECG.

Typical “sinus” P waves that precede each QRS complex, which are upright in leads I, II and aVF, are suggestive of sinus tachycardia, meaning it’s originating from the sinoatrial or SA node.

Now, go back to history and physical findings to determine the cause of sympathetic stimulation, which can be either physiologic or non-physiologic.

First, let’s start with physiologic stimulation.

If your patient presents with physiologic stressors, like pregnancy, anxiety, pain, or exercise, consider physiologic sinus tachycardia from a non-pathologic stressor.

On the other hand, if an individual has evidence of acute illness, like fever, dyspnea, or pallor, evaluate for pathologic conditions that can cause sinus tachycardia like infections, anemia, dehydration, or pulmonary embolism. In these patients you should think of physiologic sinus tachycardia from a pathologic condition.

Now, let’s go back and take a look at non-physiologic causes of sympathetic stimulation.

If the workup reveals no obvious physiologic cause, but the individual reports symptoms like palpitations, fatigue or syncope, you should evaluate for heart rate changes related to posture. Check the patient’s heart rate when they move from a supine to standing position.

Once they stand up, if their heart rate increases by 30 beats per minute from baseline, or if it exceeds 120 beats per minute within 10 minutes, in the absence of postural hypotension you can diagnose postural orthostatic tachycardia syndrome, or POTS for short.

On the other hand, if the sinus tachycardia is symptomatic but unrelated to postural changes, you can diagnose inappropriate, or non-physiologic sinus tachycardia.

Now let’s go back to the ECG and take a look at focal atrial tachycardia.

In some cases of supraventricular tachycardia, the atrial activity shows P waves that are abnormal in morphology or deflection, but they’re consistent in appearance. This is focal atrial tachycardia, meaning the electrical impulse is coming from a spot in the atrium that’s outside of the SA node.

Now, let’s take a look at atrioventricular nodal reentrant tachycardia.

Suppose you can’t see P waves at all, or if they’re just before or after the QRS complex, diagnose typical atrioventricular nodal reentrant tachycardia, or typical AVNRT. This type of tachycardia occurs when there’s a reentry circuit within the AV node.

Now, here’s a clinical pearl to keep in mind! An individual presenting with typical AVNRT typically reports “neck pounding,” a symptom that occurs as the right atrium contracts against a closed tricuspid valve.