emDOCs Podcast: Episode 108 – Unexplained Sinus Tachycardia Mental Model

Background:

• When a patient in the ED has sinus tachycardia our job as emergency physicians is to identify and treat of the underlying pathology. This is done with a HPI, review of systems, physical exam, and as indicated further diagnostic studies.
• The full differential diagnosis of sinus tachycardia in isolation is extensive ranging from benign etiologies such as anxiety to severely life threatening etiologies such as sepsis.  Discharging a patient with abnormal vital signs has been linked to unanticipated death (1-4).
  • One study when looking at a population of patients that had unexpected death within 7 days of ED discharge found that of those that had abnormal vital signs at time of discharge tachycardia was present in 83% of the cases(4,5).
  • Another study looking at patients with early death after being discharged from the ED found that tachycardia was the most common abnormal vital signs and that it tended to persist despite interventions (5).
  • A study looking at revisits in a pediatric population found that while tachycardia at discharge was independently associated with an increased risk in ED revisit rate (relative risk of 1.3), there was no clinically important intervention required at this revisit (6)
• What do we do when we are not able to explain the tachycardia or the patient is not responding to treatment as expected? At this point there are two large questions.
  • #1. Am I missing anything?
  • #2. What is this patient’s disposition?

Pathophysiology and Etiology:

• In adults, sinus tachycardia is a heart rate greater than 100 beats per minute (bpm) originating from the sinoatrial (SA) node.
• Pediatric rate cut off for tachycardia varies with age but again is defined as a heart rate great than what the normal appropriate resting heart rate for that particular age range.
• Extensive differential, and the elevation in heart rate may be normal under stress or during exercise.
• Regarding emergent underlying causes, it may be helpful to think of etiologies of tachycardia as anything that could cause a need for increased cardiac output. This cardiac output increase is often due to need for increased oxygen delivery.
  • Hypoxia, hemorrhage, or even fever can increase the demand of tissue for oxygen and thus lead to a compensatory increase in heart rate.
  • Tachycardia may be present both from many medications or drugs, as well as withdrawal.
• Many of these underlying etiologies will be obvious initially based on the history and exam.

The Mental Model:

• A mental model for sinus tachycardia can assist. Of note, this mental model is for patients where no obvious cause has been found or the patient is not responding to treatment as expected.

Vital Signs:

• Start with double checking vital signs. Do they have any other explanation on their vitals that could contribute to the heart rate?
• Heart Rate
  • Does the patient still have tachycardia?
  • Has there been any change increase or decrease after intervention?
• Blood Pressure
  • What is the patients blood pressure trend?
  • Have they had any hypotension?
  • Do they have a widened or narrowed pulse pressure?
• SPO2
  • Any hypoxia?
  • Are we getting a good waveform on the SPO2?
    • Poor waveforms more often indicate decreased perfusion than hypoxia.
•  Respiratory Rate
•  Temperature
  • Do we have a recent and accurate temperate?
    • A core temperature may be indicated.
•  Glucose POC

ECG: 

• Is this actually sinus tachycardia? Looking at the initial or even repeating the ECG will be helpful here.
  • QRS (wide/narrow)
  • Regular/Irregular
• In general sinus tachycardia should be regular and narrow complex (excluding having a bundle branch block), and wide complex tachycardia should be assumed to be ventricular tachycardia until proven otherwise.
• P waves?
  • Are there p waves or is this possibly another SVT?
• Origin from SA node?
  • Upright p waves in I, II, aVL
  • Negative p waves aVR
• Flutter?
  • Then ask are we missing another underlying arrhythmia such as Atrial Flutter. Think about this especially with the rate being consistently around 150 bpm (+/-20 bpm)

History:

• Repeat ROS
• Infectious
• Cardiopulmonary
• Tox
  • Ingestion or withdrawal
• Ask: Have we done a comprehensive review of symptoms? Have we asked about any possible infectious etiologies for the patient’s symptoms? Is there any history of medications or substances that could be causing the tachycardia either from acute ingestion or withdrawal? Is the patient having any shortness of breath at rest or with exertion?

Exam: 

• Is there anything we have overlooked on physical exam? A more detailed exam may provide a clue to the underlying etiology.
• General
  • On repeat assessment how does the patient generally appear, what is your overall gestalt?
• Cardiopulmonary
  • Are there any abnormal sounds that may point to a diagnosis?
• Abdominal Tenderness?
• Neuro/Tox
  • Pupils
  • Clonus/Rigidity
  • Reflexes
  • All may help indicate another underlying cause such as toxic ingestion or withdrawal.
• Skin
  • Diaphoretic/Dry?
    • May point to Toxic or infectious etiology
  • Infections/Wounds/Rashes
    • Have we overlooked an infectious source?
    • Axilla, Sacral, GU
• Overall Volume Status?
  • Do they have edema?
  • JVD?
  • How are their mucous membranes?

POCUS:

• RUSH exam (Rapid Ultrasound for Shock and Hypotension)
  • While derived to help identify unexplained hypotension, if we accept that sinus tachycardia may be an early indicator of shock, we can utilize this general approach to help reevaluate as clinically indicated.
• Are there signs of pericardial effusion or tamponade? Are the ventricles normal sized? How is the cardiac squeeze? Any signs of fluid or PTX in the lungs? Does the IVC indicate to you that the patient is severely volume up or down. Any signs of AAA? Any signs of free fluid in the abdomen?

Diagnostics:

• Are there any laboratory abnormalities that either we overlooked or need to consider adding on?
• CBC
• Electrolytes
• TSH
• D-Dimer
  • Is this patient low to intermediate risk for pulmonary embolism?
• Tox
  • Ethanol
  • ASA/APAP
  • Serum Osm
    • On repeat exam is there any more concern for toxic ingestion we may consider adding on APAP/ASA or looking for toxic alcohols.
•  Lactate
•  Troponin
  • Could this be ACS or myocarditis?
• Is there additional imaging indicated?
• Importantly, this is not saying just blindly order all of these labs is necessary; only order if clinically indicated. These are listed here as a cognitive stop point: have we at least considered these possible life threats?

Treatments:

• Have we adequately treated possible underlying causes?
• IVF
  • Have we rehydrated as clinically indicated?
• Analgesia
  • Have we provided adequate analgesia?
• Benzos
  • Are they requiring benzodiazepines for withdrawal?
• Additional resuscitation
  • Have we addressed all potential sources of shock for the patient in front of us? Does the patient require blood, a procedure to address obstructive shock, or other source control?
• Iatrogenic
  • Is it possible they weren’t tachycardia to begin with but we have given them something to stimulate the heart rate such as albuterol?
•  Utilizing this mental model provides a thorough approach to the patient with continued unexplained sinus tachycardia.

Disposition:

• Can we discharge the patient in sinus tachycardia? In short: yes, but it depends.
• Varies based on providers risk tolerance, patient status, and ability to follow up. Let’s use the example of the well appearing patient, without significant comorbidities. They may have presented due to palpitations or noticing their heart rate was elevated on a home monitoring device. In this case let us say we have a patient with either:
  • Asymptomatic but persistent sinus tachycardia
  • Sinus tachycardia with a found/treated underlying etiology that would otherwise not make you concerned for discharge if not for the heart rate.
• There are other conditions such as inappropriate sinus tachycardia and sinus node reentry tachycardia that could be causing this. It is not unreasonable to arrange for cardiology evaluation.

What are the risks of of discharging a patient with unexplained sinus tachycardia? 

• Patients can develop a tachycardia-mediated cardiomyopathy from any tachyarrhythmia.
• The risk seems to be greatest once reaching 110-120 bpm, and the older the patient the higher likelihood they are at risk for this.
• The time course appears to be months to years. Given this, it may be reasonable to discharge if patient is able to get reliable cardiology follow up in a short period of time.

Pearls:

• Sinus Tachycardia is often the first sign something more insidious is wrong with the patient.
• Tachycardia can be a response to anything that causes the body to have an increased oxygen demand, sympathetic stimulus, or withdrawal of a substance.
• In the ED, our job is to identify and treat underlying causes.
• When no cause is found, or the patient is not responding to treatment as expected, a more systematic mental model is needed.
• Disposition of sinus tachycardia depends on many factors, however the well-appearing asymptomatic patient does not require admission for tachycardia alone.

#FOAMed:

• https://www.emdocs.net/why-is-my-patient-still-in-sinus-tachycardia/
• http://www.emdocs.net/r-e-b-e-l-em-the-approach-to-the-most-common-cardiac-dysrhythmia-8-causes-of-sinus-tachycardia/
• https://www.aliem.com/paucis-verbis-an-approach-to-persistent-tachycardia/
• https://ddxof.com/sinus-tachycardia/

References:

1. Henning A, Krawiec C. Sinus Tachycardia. In: StatPearls. Treasure Island (FL): StatPearls Publishing; April 30, 2022.
2. Yusuf S, Camm AJ. Deciphering the sinus tachycardias. Clin Cardiol. 2005;28(6):267-276. doi:10.1002/clc.4960280603
3. Yusuf S, Camm AJ. The sinus tachycardias. Nat Clin Pract Cardiovasc Med. 2005;2(1):44-52. doi:10.1038/ncpcardio0068
4. Sklar DP, Crandall CS, Loeliger E, Edmunds K, Paul I, Helitzer DL. Unanticipated death after discharge home from the emergency department. Ann Emerg Med. 2007;49(6):735-745. doi:10.1016/j.annemergmed.2006.11.018
5. Gabayan GZ, Sun BC, Asch SM, et al. Qualitative factors in patients who die shortly after emergency department discharge. Acad Emerg Med. 2013;20(8):778-785. doi:10.1111/acem.12181
6. Wilson PM, Florin TA, Huang G, Fenchel M, Mittiga MR. Is Tachycardia at Discharge From the Pediatric Emergency Department a Cause for Concern? A Nonconcurrent Cohort Study. Ann Emerg Med. 2017;70(3):268-276.e2. doi:10.1016/j.annemergmed.2016.12.010
7. Brugada J, Katritsis DG, Arbelo E, et al. 2019 ESC Guidelines for the management of patients with supraventricular tachycardia: The Task Force for the management of patients with supraventricular tachycardia of the European Society of Cardiology (ESC) [published correction appears in Eur Heart J. 2020 Nov 21;41(44):4258]. Eur Heart J. 2020;41(5):655-720. doi:10.1093/eurheartj/ehz467
8. Fleming S, Thompson M, Stevens R, et al. Normal ranges of heart rate and respiratory rate in children from birth to 18 years of age: a systematic review of observational studies. Lancet. 2011;377(9770):1011-1018. doi:10.1016/S0140-6736(10)62226-X
9. Kim DY, Kim SH, Ryu KH. Tachycardia induced Cardiomyopathy. Korean Circ J. 2019;49(9):808-817. doi:10.4070/kcj.2019.0199