Electrocardiograms (ECGs) are a fundamental tool in cardiology, providing critical insights into heart function and potential abnormalities. As part of my work supporting an initiative in India to collect mobile ECG data, I've had the opportunity to explore the formats and quality of several devices used in our observational study. This data will help develop AI models that can detect cardiac diseases using more affordable sensors than those currently available in primary healthcare facilities. In this post, I'll share how ECGs are used to detect cardiac issues, the technology behind mobile ECG devices like the Kardia series we are using, factors affecting measurement quality, and how everything aligns with our goals for tight feedback loops that help us adjust the collection process while the observational study is still underway.

How ECGs Detect Cardiac Abnormalities

An electrocardiogram (commonly known as ECG or EKG, depending on who you are speaking with) records the electrical activity of the heart over time. This electrical activity coordinates the contraction and relaxation of the heart chambers, ensuring efficient blood flow throughout the body.

The Basics of ECG Interpretation

A standard ECG tracing shows several distinct waves and intervals:

• P wave: Represents atrial depolarization (when the upper chambers of your heart contract to push blood to the lower chambers)
• QRS complex: Represents ventricular depolarization (when the powerful lower chambers contract to pump blood to your body and lungs)
• T wave: Represents ventricular repolarization (when the lower chambers relax and refill with blood)
• PR interval: Time from the beginning of the P wave to the beginning of the QRS complex (shows how quickly electrical signals travel from the upper to lower chambers)
• QT interval: Time from the beginning of the QRS complex to the end of the T wave (represents the total time of ventricle contraction and relaxation)

Common Abnormalities Detected by ECGs

1. Arrhythmias: Irregular heart rhythms, including:
   • Bradycardia: Abnormally slow heart rate (< 60 BPM)
   • Tachycardia: Abnormally fast heart rate (> 100 BPM)
   • Atrial fibrillation: Irregular and often rapid heart rate
   • Ventricular fibrillation: Rapid, irregular ventricular contractions
2. Conduction Abnormalities:
   • Heart blocks: Delays or interruptions in the electrical impulses
   • Bundle branch blocks: Delays in conduction to the ventricles
3. Structural Issues:
   • Ventricular hypertrophy: Enlarged heart chambers
   • Myocardial infarction (heart attack): Damage to heart muscle
   • Pericarditis: Inflammation of the sac around the heart
4. Electrolyte Imbalances:
   • Abnormal levels of potassium, calcium, or magnesium

Mobile ECG Devices

AliveCor's Kardia devices bring clinical-grade ECG recording to mobile devices, but are not currently used as standard screening equipment for referring patients upstream to a primary healthcare facility or cardiology clinic in India’s healthcare system. These portable devices allow patients to record their own ECGs anywhere, anytime. Out of all the devices we are using, the Kardia 1-6L device has my favorite user experience and I find it to be the most reasonable for field level use based on a combination of simplicity, ruggedness and battery life.

Kardia Devices Lineup

The Kardia product line includes:

1. Kardia Mobile (1-lead): The original device that records a single-lead ECG (equivalent to Lead I in a standard 12-lead ECG). While a prior study we are basing our efforts on used this device, we opted for a device with more leads (think touch points on the skin).
2. Kardia Mobile 6L (6-lead): An advanced device that can record six leads (I, II, III, aVL, aVR, aVF) by placing the device on the left knee with thumbs on the top electrodes. It has two sensors on the top and one on the bottom so you can use fingers from both hands and a knee or ankle to generate a 6 lead snapshot of your data.

How ECG Devices Work

Kardia devices use metal electrodes to detect the electrical signals from the heart. When you place your fingers on these electrodes, the device captures the electrical activity and transmits it to a smartphone app via ultrasonic signals.

The app then:

• Displays the ECG in real-time
• Stores the recording for later review
• Analyzes the ECG for potential abnormalities