Changes in QRS complex in dogs with normal and exaggerated tidal volumes

Area of Science:

• Cardiovascular Physiology
• Respiratory Physiology
• Electrocardiography

Background:

• The electrocardiogram (ECG) reflects cardiac electrical activity.
• Ventilation can influence ECG parameters due to thoracic electrical field changes.

Purpose of the Study:

• To investigate the impact of normal and exaggerated ventilation on QRS amplitudes in dogs.
• To determine if hyperinflation affects ECG voltages and to explore potential mechanisms.

Main Methods:

• 10 dogs were studied using 12-lead ECG during eupnea and hyperinflation.
• Hyperinflation was induced via intermittent positive pressure ventilation and negative extrathoracic pressure.
• Radiography was used to assess heart position and size during hyperinflation.

Main Results:

• No significant QRS voltage changes were observed during normal breathing (eupnea).
• Hyperinflation (10 mm Hg transpulmonary pressure) led to decreased QRS voltages in leads I, V10, rV3, and aVF.
• Heart displacement to the non-dependent thorax and reduction in heart size were observed during hyperinflation.

Conclusions:

• Exaggerated ventilation, specifically hyperinflation, demonstrably alters canine ECG QRS voltages.
• Changes in heart-electrode proximity and altered volume conductor properties likely contribute to voltage variations.
• Findings highlight the mechanical influence of respiratory mechanics on cardiac electrical measurements.