Electrocardiogram (ECG)

An electrocardiogram (ECG) is an essential diagnostic tool that provides valuable insights into cardiac function. It can identify current heart conditions such as arrhythmias, which may require pacemaker implantation or pharmacologic management, as well as past events like silent myocardial infarctions or myocardial damage. Additionally, ECGs can detect structural changes, such as heart enlargement, which may contribute to heart failure, and can be crucial in the immediate identification of acute myocardial infarctions, enabling timely interventions to reduce cardiac damage and improve survival rates.

Clinical Indications for an ECG

Symptomatic Patients

• Chest pain.

• Syncope or pre-syncope.

• Dizziness.

• Shortness of breath.

• Palpitations.

Suspected Cardiac Conditions

• Acute myocardial infarction.

• Silent myocardial infarction.

Limitations of an ECG

While the ECG is a valuable diagnostic tool, it has certain limitations:

1. Intermittent Arrhythmias: ECG captures cardiac activity only at the time of recording, potentially missing transient rhythm abnormalities. For these cases, ambulatory monitoring (e.g., Holter monitoring) is recommended.

2. False Negatives: ECG findings may appear normal in patients with undiagnosed coronary artery disease (CAD) or other forms of heart disease.

3. False Positives: Apparent abnormalities on an ECG may not have clinical significance after a comprehensive evaluation.

Clinical Indications for Ambulatory Monitoring (Holter Monitoring)

Ambulatory monitoring is recommended when symptoms such as dizziness, fainting, low blood pressure, prolonged fatigue, or palpitations persist without a definitive diagnosis from a resting ECG. Extended monitoring over 7 or 14 days allows detection of transient or intermittent arrhythmias.

Clinical Indications for Stress Echocardiography

Given the limitations of ECGs in certain scenarios, stress echocardiography offers enhanced diagnostic accuracy. It is particularly valuable for:

• Patients presenting with possible acute coronary syndrome (ACS) and non-diagnostic ECG findings.

• Evaluation of typical anginal symptoms of coronary artery disease (CAD) or ischemic equivalent, whether exertional or non-exertional.

• Syncope evaluation in patients with suspected cardiac causes.

Stress echocardiography is more sensitive than exercise treadmill stress testing alone in detecting CAD and is instrumental in identifying multi-vessel disease. Furthermore, it provides a reliable prognosis for patients with suspected or established CAD.

Indications for Stress Echocardiography

Stress echocardiography is indicated for:

1. Initial Evaluation: Patients with intermediate (e.g., hypertension, diabetes, dyslipidemia, smoking history, or family history of premature CAD) or high global CAD risk.

2. Re-Evaluation: Stable patients with known CAD, including those with a history of myocardial infarction (MI), ACS, or abnormal stress imaging.

(Source: Standards for Provision of Echocardiography in Ontario, 2021)

For a comprehensive list of stress echocardiography indications and additional information about stress echo modalities, including contrast stress echocardiography, please visit our "For Doctors: Stress Echo" section.

Report Processing

The ECG report is meticulously analyzed by a cardiologist. A detailed report, including conclusions and clinical recommendations, is sent directly to the referring physician. This ensures that patients receive timely and accurate follow-up care.

Next Steps

To refer a patient for an ECG, Holter monitoring, Stress Echocardiography, or any other diagnostic modality, please download the Requisition Form and fax it to our Requisition Processing Centre at 647-351-6648.