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FACT SHEET: Myocardial Infarction (also known as “MI”, “heart attack”, “coronary occlusion”, and “coronary thrombosis”; is a form of “acute coronary syndrome” [ACS]1)

Date of Publication: September 6, 2019

Note: This fact sheet focuses on acute myocardial infarction (AMI) in the context of dental hygiene care. For guidance regarding post-myocardial infarction care, please refer to the dedicated fact sheet on this topic.

Is the initiation of non-invasive dental hygiene procedures* contra-indicated?

  • Yes, if patient/client exhibits signs/symptoms of acute myocardial infarction. AMI is a medical emergency — 911 should be called, and supportive care should be provided pending arrival of emergency medical services (EMS).
  • Yes, if patient/client has had an MI within the past 4 to 6 weeks, with functional capacity (FC) needing to be determined before proceeding with professional oral care. Refer to Post-MI fact sheet  for further guidance.

Is medical consult advised?  

  • Yes, if patient/client’s medical status is suspected to be unstable.

Is the initiation of invasive dental hygiene procedures contra-indicated?**

  • Yes, if patient/client exhibits signs/symptoms of AMI. See above.
  • Yes, if patient/client has had an MI within the past 4 to 6 weeks. See above, and refer to Post-MI fact sheet for further guidance. 

Is medical consult advised? 

  • See above.

Is medical clearance required? 

  • Yes, if there are medical complications or comorbid conditions post-MI that may impact patient/client safety.

Is antibiotic prophylaxis required?  

  • No.

Is postponing treatment advised?

  • Yes, if the MI has occurred within the past 4 to 6 weeks or functional capacity is less than four METs2.

Oral management implications

  • History-taking by the dental hygienist can identify patients/clients at elevated risk of having an MI. (Refer to risk factors for MI under “Related signs and symptoms” below.) As appropriate, a stress reduction protocol can be utilized to minimize the potential adverse effects of stress that contribute to increased cardiac workload (and hence increased risk of MI).
  • Persons who have unstable angina or have previously had an MI (especially very recently) are at particular periprocedural cardiovascular risk. See Post-Myocardial Infarction Fact Sheet for additional information.
  • AMI is a medical emergency — 911 should be promptly called if a patient/client exhibits signs/symptoms of myocardial infarction in the dental hygiene office. All oral procedures should be terminated. The patient/client should be instructed to stop all activity. Supportive care should be provided pending arrival of emergency medical services (EMS).  
  • For the adult patient/client with suspected MI in the dental/dental hygiene office who is conscious and responsive pending arrival of EMS:
    • Positioning: Place patient/client in a comfortable position (which may not be the supine position, because air hunger may be associated with orthopnea3; sitting is sometimes preferred).
    • Airway: Ensure open airway. 
    • Breathing: Ensure adequate breathing by communicating with and reassuring patient/client.
    • Circulation: Monitor pulse and blood pressure. 
    • Dispense/administer:
      • Oxygen at flow rate of 5 to 6 L/minute.
      • Nitroglycerin (at normal dose if patient/client already has had this prescribed [e.g., for angina]; nitrates in all forms are contraindicated in patients/clients with initial systolic pressure < 90 mm Hg or < 30 mm Hg below baseline value4).
      • ASA5 325 mg tablet or two 80 mg tablets (non-enteric coated) for chewing followed by swallowing (which speeds up anti-platelet action versus immediate swallowing).
    • Ensure that vital signs, drug administration, and patient/client responses are monitored and recorded.
    • Facilitate/ensure next steps in medical care (i.e., transport to hospital), and reassure patient/client.
  • If MI progresses to cardiac arrest (no pulse) and patient/client is unresponsive before arrival of EMS:
    • Initiate cardiopulmonary resuscitation (CPR).
    • Use Automated External Defibrillator (AED).6

Oral manifestations

  • None are specific to myocardial infarction, although pain may be experienced in the jaw and teeth, and cyanosis of the lips and/or mucous membranes may occur.

Related signs and symptoms

  • 600,000 Canadian adults live with a history of myocardial infarction, with about 64,000 Canadians experiencing a first MI annually. 
  • AMI7 occurs when there is blockage in one or more of the coronary arteries (i.e., the vessels that provide blood supply to the myocardium8), which results in blood (and hence oxygen) deprivation to the affected area(s) of the myocardium. This results in death of, or permanent damage to, the myocardium. MI usually results from the build-up of atherosclerotic plaque in the coronary arteries, which results in a complete or near-complete blockage, or is associated with a blood clot. More rarely, sudden, significant physical or emotional stress, or a spasm of a coronary artery, can trigger infarction. 
  • Risk factors for MI, typically a manifestation of ischemic heart disease, include: advanced age, hypertension, diabetes mellitus, obesity, kidney disease, hyperlipidemia, smoking, physical inactivity, excessive alcohol consumption, recreational drug use (such as cocaine or amphetamines), male gender, family history of coronary artery disease, and past history of MI. Persons of indigenous (First Nations, Métis, and Inuit), South Asian, and African heritage are at increased risk of MI due to elevated rates of risk factors such as diabetes and hypertension.
  • Symptoms associated with AMI are often similar to those experienced with angina pectoris, but chest pain, when present, persists for a longer period of time.
  • Chest pain (which may be described as tightness, heaviness, squeezing, or burning in character) is characteristic (but not always present). Such pain is usually across the anterior precordium (substernal) and may radiate to the jaw, neck, arms (left more frequently than right), back, and epigastrium. Pain may also be experienced in the neck, shoulder, arms, back, or abdomen. Pain may vary in intensity, but is usually sudden and persists for more than 15 to 20 minutes. In contradistinction to angina, the pain of an MI is incompletely relieved, or not at all relieved, by rest or nitrates (e.g., nitroglycerin tablets or spray).
  • Diaphoresis (i.e., excessive sweating) and breathing problems (including shortness of breath, difficulty breathing, wheezing, and cough) are common signs/symptoms.
  • Other signs/symptoms may include: cyanotic, ashen, or pale appearance; cool, clammy skin; intestinal discomfort; nausea (with or without vomiting); light-headedness; syncope; irregular pulse with palpitations; air hunger; sense of impending doom; and fear.
  • MI may present atypically — particularly in women, older persons, and persons with certain co-morbidities (including diabetes, dementia, heart failure, and pacemakers) — sometimes being clinically silent at onset.
  • MI is rare in children and adolescents, when the cause is usually acute inflammation of the coronary arteries or anomalous origin of the left coronary artery.
  • Cardiac dysrhythmias may occur in the early post-infarction period (1 to 2 hours post-infarct). Death in the early post-infarction period usually results from acute dysrhythmia, although it may also result from the infarction of a large amount of myocardium.
  • Cardiogenic shock occurs in about 10% to 15% of patients/client with acute MI who survive long enough to reach the hospital. It typically develops about 10 hours after the onset of the infarction, resulting from cardiac dysrhythmias, continued severe chest pain, onset of pulmonary edema, or pulmonary embolism. Signs include hypotension (systolic BP < 80 mm Hg) and stigmata of inadequate peripheral circulation (e.g., cool skin, peripheral cyanosis, tachycardia, decreased urinary output, and confusion). It is often fatal.
  • Survival after myocardial infarction depends on many factors, particularly the state of left ventricular function and severity of obstructive lesions in the coronary vasculature, as well as timely access to intravenous thrombolytic therapy9 and/or percutaneous coronary intervention (PCI, which includes placement of stents and balloon angioplasty). AMI is associated with a 30% mortality rate; nearly half of deaths occur before the patients/clients reach a hospital, and 5% to 10% of survivors die within one year post-infarction. Patients/clients who experience residual heart failure typically die within 1 to 5 years.

References and sources of more detailed information

Date: August 6, 2019
Revised: October 15, 2023


1 ACS includes: unstable angina; ST-elevation myocardial infarction (STEMI, which entails complete blockage of a coronary artery); and non-ST-elevation myocardial infarction (NSTEMI, which entails partial blockage in a major coronary artery). ST-elevation refers to a specific finding on an electrocardiogram (ECG).
2 MET = metabolic equivalent. The following questions reflect abilities that meet the four MET level:

  • Can you walk up a flight of stairs carrying groceries?
  • Can you run a short distance?
  • Can you participate in recreational activities such as doubles tennis, play nine holes of golf, or dance for at least five minutes?

3 orthopnea = shortness of breath when lying in recumbent position
4 Nitrates are also contraindicated if there has been recent (24 to 48 hours, depending on specific drug) phosphodiesterase-5 inhibitor use (e.g., sildenafil or other similar erectile dysfunction medications).
5 ASA = acetylsalicylic acid (Aspirin)
6 Each dental hygienist in clinical practice in Ontario must hold a current CPR certificate at the basic life support level, which is to include training in the use of an AED.
7 There are 2 major types of acute MI: STEMI (ST-segment elevation AMI, with ST-segment elevation referring to the appearance of the electrocardiogram [ECG]) and NSTEMI (non-ST-segment elevation AMI). NSTEMI tends to have a higher incidence of recurrent ischemia and reinfarction.
8 myocardium = cardiac (heart) muscle
9 Early thrombolytic therapy for STEMI patients/clients includes streptokinase, alteplase (t-PA), reteplase, and tenecteplase.

* Includes oral hygiene instruction, fitting a mouth guard, taking an impression, etc.
** Ontario Regulation 501/07 made under the Dental Hygiene Act, 1991. Invasive dental hygiene procedures are scaling teeth and root planing, including curetting surrounding tissue.