What clue on an anterior 12-lead electrocardiogram (ECG) indicates right-sided heart involvement in a myocardial infarction (MI)?

ECG Clues for Right Ventricular Involvement in Anterior Myocardial Infarction

ST-segment elevation in lead V1 is the most important clue on a standard 12-lead ECG that suggests right ventricular involvement in anterior myocardial infarction. 1

Pathophysiology and ECG Manifestations

When evaluating a patient with suspected anterior myocardial infarction, identifying right ventricular involvement is crucial as it significantly impacts morbidity, mortality, and management decisions. The standard 12-lead ECG provides initial clues, but additional leads may be necessary for definitive diagnosis.

Key ECG Findings on Standard 12-Lead ECG:

1. ST-segment elevation in lead V1:

   • When present with other anterior MI changes, ST elevation in V1 may indicate right ventricular involvement 1
   • This occurs because lead V1 is positioned close to the right ventricle and can detect right ventricular injury currents

2. ST-segment vector direction:

   • In anterior MI with right ventricular involvement, the spatial vector of the ST-segment shift is directed to the right and anteriorly 1
   • This rightward vector direction causes more prominent ST elevation in V1 compared to other anterior leads

Confirming Right Ventricular Involvement

While V1 elevation provides a clue, definitive diagnosis requires additional right-sided precordial leads:

1. Right-sided chest leads:

   • V3R and V4R are the most valuable for confirming right ventricular involvement 1
   • ST-segment elevation ≥0.1 mV in V4R has 100% sensitivity and 87% specificity for proximal right coronary artery occlusion 2

2. Timing considerations:

   • ST elevation in right-sided chest leads persists for a much shorter time than ST elevation in other leads 1
   • Recording right-sided leads as rapidly as possible after symptom onset is critical 1

Clinical Implications and Management

Recognizing right ventricular involvement in anterior MI has important implications:

1. Coronary anatomy correlation:

   • Anterior MI with right ventricular involvement typically indicates proximal left anterior descending (LAD) artery occlusion 3
   • QS complexes in leads V3R and V4R in the chronic phase of anterior wall MI suggest right ventricular infarction when proximal LAD is occluded 3

2. Management considerations:

   • Patients with right ventricular involvement have higher morbidity and mortality rates
   • These patients require careful fluid management and may be preload-dependent
   • Avoiding nitrates and other preload-reducing medications is crucial

Pitfalls and Caveats

1. Limited sensitivity of standard 12-lead ECG:

   • The standard 12-lead ECG alone has limited sensitivity for detecting right ventricular involvement
   • Always consider recording right-sided leads (V3R-V4R) when anterior MI is suspected, especially with ST elevation in V1

2. Time-dependent changes:

   • Right ventricular ST changes may resolve quickly, making early ECG acquisition essential 1
   • A normal ECG does not exclude right ventricular involvement if obtained late after symptom onset

3. Differential diagnosis:

   • ST elevation in V1 can also occur in other conditions (RBBB, Brugada syndrome, pericarditis)
   • Clinical correlation and additional right-sided leads help distinguish these entities

In conclusion, ST elevation in lead V1 on a standard 12-lead ECG should raise suspicion for right ventricular involvement in the setting of anterior myocardial infarction. However, recording additional right-sided precordial leads (V3R and V4R) is essential for definitive diagnosis and should be performed as early as possible after symptom onset.