A 72-year-old patient with a prior myocardial infarction presents with palpitations. The monitor shows a regular wide-complex tachycardia at 168 beats per minute. The patient is alert, the blood pressure is 118/72 mmHg, and a 12-lead ECG from six months ago is available.

Before reading further, answer three questions:

1. What must you assess before trying to name the rhythm?

2. What belongs in the differential diagnosis of a wide-complex tachycardia?

3. What can the baseline ECG contribute that the tachycardia tracing cannot provide by itself?

Keep your answers in mind. We will return to the case.

First question: is the patient unstable?

Rhythm interpretation matters, but physiology comes first.

Look for hypotension, altered mental status, shock, ischemic chest discomfort, or acute heart failure attributable to the tachyarrhythmia. Current American Heart Association guidance recommends synchronized cardioversion for hemodynamically unstable wide-complex tachycardia.

Our patient is presently stable, which gives us time to obtain a high-quality 12-lead ECG, examine the clinical context, and seek expert input while continuing appropriate monitoring.

A stable blood pressure does not prove that a wide-complex rhythm is supraventricular. Stability tells you about the patient’s current physiology—not the site of rhythm origin.

Second question: what can make a tachycardia wide?

A wide QRS tells us that ventricular activation is not occurring through the usual rapid, near-simultaneous His-Purkinje sequence. That can happen through several mechanisms:

• Ventricular tachycardia: activation begins in ventricular myocardium.

• SVT with fixed or rate-related aberrancy: a supraventricular impulse encounters bundle-branch delay or block.

• Pre-excited tachycardia: ventricular activation uses an accessory pathway.

• Ventricular pacing: activation begins at the pacing site and spreads sequentially.

• Toxic or metabolic conduction slowing: for example, sodium-channel blockade or hyperkalemia.

• Artifact: always worth considering when the tracing and the patient tell different stories.

The task is not simply to recognize that the QRS is wide. It is to determine why it is wide.

Third question: what changed from baseline?

When a previous ECG exists, put the two tracings side by side.

Do not ask only, “Does the patient have a bundle-branch block?” Ask:

• Is the QRS configuration during tachycardia similar to the baseline pattern?

• Has the frontal QRS axis changed substantially?

• Are the precordial morphology and transition recognizably different?

• Has the overall QRS amplitude or distribution changed?

• Does the baseline tracing show pre-excitation, prior infarction, conduction disease, or pacing?

A tachycardia QRS that closely resembles a patient’s fixed baseline bundle-branch block can support SVT with aberrancy. A marked change in axis or morphology strengthens the case for VT. Historical work has identified an axis shift greater than approximately 40 degrees as a particularly useful clue.

But this comparison is evidence—not a verdict. Similarity does not absolutely exclude VT, and difference does not replace a complete interpretation.

The practical principle

The larger the change between the baseline QRS and the wide-complex tachycardia QRS, the more strongly the comparison may point toward ventricular origin.

This is powerful because it changes the question. Instead of judging an unfamiliar wide tracing in isolation, you are measuring how far ventricular activation has moved away from that patient’s known pattern.

Return to the case

The baseline ECG shows sinus rhythm with a right bundle-branch block. During tachycardia:

• The frontal QRS axis shifts by roughly 70 degrees.

• The morphology in V1 no longer resembles the baseline right bundle-branch pattern.

• The precordial transition changes substantially.

What is the best conclusion?

A. The stable blood pressure makes VT unlikely.
B. The existing bundle-branch block proves SVT with aberrancy.
C. The marked axis and morphology changes increase the likelihood of VT.
D. The rate alone can reliably distinguish VT from SVT.

Answer: C. The baseline comparison adds meaningful evidence for VT. The patient’s stability and rate do not reliably establish rhythm origin, and the presence of baseline bundle-branch block does not end the analysis.

Five habits worth keeping

1. Assess stability before elegance. Treat the patient’s physiology first.

2. Get the 12-lead. A monitor strip rarely gives you everything you need.

3. Find the old ECG. “Baseline unknown” and “baseline unchanged” are very different statements.

4. Use multiple clues. Axis, morphology, AV relationship, clinical history, and validated criteria belong together.

5. Respect uncertainty. Undifferentiated WCT deserves a safety-conscious approach and expert consultation.

Turn one challenge into a complete learning path

The free newsletter gives you one focused cardiology challenge each week. The full EKG Guy platform lets you go further with structured ECG and cardiovascular courses, thousands of explained practice questions, adaptive study tools, an AI tutor, and a community of healthcare professionals.

What we’re excited to keep building

We are making practice more personal. The Cardiovascular QBank and AI tutor can help you turn a missed question into a focused next step: revisit the concept, work through the reasoning, and choose what to study next. Each weekly challenge is a starting point; the platform is where you can keep building the skill.

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Use the trial to explore the wide-complex tachycardia lessons, test your interpretation process, and identify the steps that still slow you down.

Next week: When the aortic valve area says “severe,” but the gradient does not.

Know a colleague who enjoys ECG puzzles? Forward this issue and compare answers before reading the explanation.

— The EKG Guy Team

Selected references

• EKG Guy Course and Lesson: Wide Complex Tachycardias—WCT Overview and WCT and Baseline ECG Comparison.

• American Heart Association. 2025 Adult Advanced Life Support: Wide-Complex Tachycardia.

• American Heart Association. Adult Tachyarrhythmia With a Pulse Algorithm.

Educational content for healthcare professionals and trainees. This newsletter does not replace bedside assessment, clinical judgment, institutional protocols, specialist consultation, or individualized medical care.

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Cardiology is learned in layers.

First, we memorize waves, intervals, pressures, and valve events. Then we begin to see how they fit together. Eventually, the tracing, the physiology, the examination, and the imaging start telling the same story.

The EKG Guy Weekly is here to help make those connections—one focused lesson at a time.

Each week, subscribers can expect a concise, practical mix of:

• ECG interpretation and pattern recognition

• Cardiovascular physiology and hemodynamics

• Echocardiography, pacemaker, and coronary angiography concepts

• Clinical cases and common diagnostic pitfalls

• Questions that test understanding—not just recall

• Links to deeper lessons and structured learning resources

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This week’s concept: the Cardiac Cycle

The cardiac cycle can look intimidating when it is presented as a crowded Wiggers diagram. But the entire sequence becomes easier when you follow one governing idea:

Electrical activation changes myocardial tension. Changing tension changes chamber pressure. Pressure gradients move blood and determine when valves open and close.

Valves do not open because the ECG reaches a particular wave. They open and close passively when the pressure gradient across them reverses.

More details can be found in Lesson 1 of the Cardiovascular Physiology course.

Let’s follow the left heart through one cycle. The right heart moves through an analogous sequence at lower pressures.

1. Ventricular filling

When left atrial pressure exceeds left ventricular pressure, the mitral valve opens. Ventricular filling begins with rapid early filling, slows during diastasis, and receives a final contribution from atrial contraction.

The P wave represents atrial depolarization; atrial mechanical contraction follows shortly afterward. By the end of filling, the ventricle has reached its end-diastolic volume.

2. Isovolumetric contraction

Ventricular depolarization appears as the QRS complex and precedes the mechanical rise in ventricular pressure.

When left ventricular pressure exceeds left atrial pressure, the mitral valve closes, contributing to S1. The aortic valve has not opened yet, so both valves are closed. Pressure rises rapidly while ventricular volume remains essentially unchanged—hence isovolumetric contraction.

3. Ventricular ejection

When left ventricular pressure exceeds aortic pressure, the aortic valve opens. Blood is ejected, initially rapidly and then more slowly, as ventricular volume falls toward its end-systolic volume.

This is an important distinction: ventricular systole begins before ejection. The isovolumetric phase is already part of systole even though no blood is leaving the ventricle.

4. Isovolumetric relaxation

As the ventricle relaxes and aortic pressure again exceeds left ventricular pressure, the aortic valve closes, contributing to S2.

Both valves are briefly closed again. Ventricular pressure falls without a meaningful change in volume. Once left ventricular pressure falls below left atrial pressure, the mitral valve opens—and the next cycle begins.

A 4-question framework

At any point in the cardiac cycle, ask:

1. What is the electrical event?

2. Which chamber has the higher pressure?

3. Which valves are open or closed?

4. Is ventricular volume rising, falling, or unchanged?

If you can answer those four questions, you can reconstruct most of the Wiggers diagram rather than memorize it.

Why this matters clinically

The cardiac cycle is not an isolated physiology exercise. It organizes cardiovascular reasoning:

• Auscultation: Systolic murmurs occur between S1 and S2; diastolic murmurs occur after S2 and before the next S1.

• Echocardiography: Valve motion, Doppler flow, filling patterns, and chamber mechanics all reflect time-dependent pressure gradients.

• Hemodynamics: Pressure-volume loops translate filling, isovolumetric contraction, ejection, and relaxation into ventricular work.

• Tachycardia: As heart rate rises, diastolic time becomes shorter. That can reduce filling time and constrain coronary perfusion, particularly when cardiovascular reserve is limited.

• Valve disease: Stenosis and regurgitation change the expected relationship among pressure, flow, volume, and heart sounds.

The goal is not simply to name each phase. It is to predict what should happen—and recognize when the observed physiology does not match.

Quick check

During isovolumetric contraction, which statement is correct?

A. The mitral valve is open and ventricular volume is increasing.
B. The aortic valve is open and ventricular volume is decreasing.
C. Both valves are closed and ventricular pressure is falling.
D. Both valves are closed and ventricular pressure is rising.

Answer: D. The mitral valve has closed, the aortic valve has not yet opened, and ventricular pressure rises at essentially constant volume.

Go deeper with The EKG Guy

This newsletter is your weekly starting point. For structured cardiovascular learning, a comprehensive practice QBank, guided learning paths, community support, and AI-assisted study tools, visit The EKG Guy.

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Whether you are learning the fundamentals, preparing for an examination, teaching trainees, or refining decisions in practice, the aim is the same: turn cardiovascular knowledge into confident clinical reasoning.

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If this issue helped you connect the tracing to the physiology, forward it to a colleague or trainee. And reply with the cardiology topic you would like us to break down next.

See you next week,

The EKG Guy Team
Learn the pattern. Understand the physiology. Apply it clinically.

Selected references

• Pollock JD, Makaryus AN. Physiology, Cardiac Cycle. StatPearls Publishing.

• Mitchell JR, Wang J-J. Expanding application of the Wiggers diagram to teach cardiovascular physiology. Advances in Physiology Education. 2014.

Educational content only. This newsletter does not replace clinical judgment, institutional protocols, formal medical training, or individualized medical advice.

Thank you to everyone who responded yesterday to the launch of our new Question Bank.

The response was incredibly encouraging.

We opened a very limited early-access discount for prior EKG Guy users and supporters, and those initial spots filled quickly. I am grateful for the support, feedback, and excitement from those who joined early.

Because several people have continued to ask about access, we are keeping a limited discount available for a short time.

The Complete Question Bank is still available for 50% off

Our new Question Bank includes 1,700+ cardiovascular questions across board-style review and diagnostic coding.

It includes:

• CV board-style multiple-choice questions

• Diagnostic coding practice

• ECG, echo, cath, pacemaker, and broader cardiovascular medicine topics

• Timed mode and tutor mode

• Detailed expert explanations

• Performance insights and weak-area tracking

• AI-powered recommendations that learn from your performance and help guide what to study next

The normal 24-month price is $299.

For a limited time, you can still use the same code to receive 50% off: QBANK24

That brings 24-month access to approximately $149.50.

How to access the offer

If you do not already have an account, create a free account here first:

https://ekgguy.com/get-started

Then:

1. Click the Pricing tab in the top-right corner.

2. Select Question Bank Complete.

3. Enter code QBANK24.

4. Continue to checkout.

Please do not wait if you are interested

The initial deepest-discount early-access spots have already been claimed, and this remaining discount is also limited.

If you are studying cardiovascular medicine, preparing for boards, reviewing ECGs, practicing diagnostic coding, or simply trying to strengthen clinical reasoning, this was built for you.

Most importantly, thank you.

Your support helps us continue building tools that make cardiovascular education more practical, more personalized, and more clinically useful.

If you have any issue accessing the offer, email us directly at:

support@theekgguy.com

Anthony Kashou, MD
The EKG Guy

It has been a while since I have shared an update here, but we have been building a lot behind the scenes.

The EKG Guy started with a simple mission: make ECG interpretation clearer, more practical, and more clinically useful.

That mission has not changed.

But over time, it became clear that cardiovascular learners need more than isolated ECG education. They need a structured way to review ECGs, echo, cath, pacemakers, diagnostic coding, and broader cardiovascular medicine — with questions, explanations, performance tracking, and guidance on what to study next.

That is why we built our new Question Bank.

Introducing our New Question Bank

Our brand-new Question Bank is now available with 1,700+ cardiovascular questions across board-style review and diagnostic coding.

It includes:

• CV board-style multiple-choice questions

• Diagnostic coding practice

• ECG, echo, cath, pacemaker, and broader cardiovascular medicine topics

• Timed mode and tutor mode

• Detailed expert explanations

• Performance insights and weak-area tracking

• AI-powered recommendations that learn from your performance and help guide what to study next

The goal is simple: help learners practice cardiovascular medicine more efficiently, identify their gaps, and know what to study next.

Early-access thank-you offer

As a thank-you to those who have supported, subscribed to, purchased from, or followed The EKG Guy over the years, we are opening a limited early-access offer.

For a limited time, you can get:

Complete Question Bank — 24 months for $24

That is about $1/month, or roughly 3¢/day, for two years of cardiovascular question-based learning.

The normal 24-month price is $299.

Use code: QBANK24

How to access the offer

If you do not already have an account, create a free account here first:

https://ekgguy.com/get-started

Get Started

Then:

1. Click the Pricing tab in the top-right corner.

2. Select Question Bank Complete.

3. Enter code QBANK24.

4. Continue to checkout.

With the 92% discount, the checkout price should show approximately $23.92.

Who this is for

This was built for students, residents, fellows, clinicians, educators, and anyone studying cardiovascular medicine.

It may be especially useful if you are:

• Preparing for cardiovascular boards

• Reviewing ECG interpretation

• Practicing echo, cath, and diagnostic coding

• Strengthening clinical reasoning

• Looking for structured question-based review

• Trying to identify weak areas and study more efficiently

Why we built it

There are many cardiovascular learning resources, but learners often need a better way to practice, get feedback, and know what to study next.

This Question Bank is our attempt to make that process more practical and more personalized.

This is still an early rollout, and we genuinely value feedback from users who try it.

Get Started

If you have any issue accessing the offer, email us directly at:

support@theekgguy.com

Thank you again for supporting The EKG Guy over the years.

More updates are coming soon.

Anthony Kashou, MD
The EKG Guy

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