3.3 Diagnostic Imaging, ECG Interpretation & Pulmonary Function Testing
Key Takeaways
- Diagnostic imaging selection requires balancing diagnostic yield against radiation exposure and contrast risks: Non-contrast head CT is mandatory first-line for acute stroke/trauma to rule out hemorrhage; CT Pulmonary Angiography (CTPA) is gold standard for pulmonary embolism; and Point-of-Care Ultrasound (POCUS) provides rapid, radiation-free evaluation of gallbladder, deep veins, and cardiac function.
- Contrast-induced nephropathy prevention requires identifying high-risk patients (eGFR <30 mL/min/1.73m²) and administering IV isotonic saline hydration; oral metformin must be held at the time of iodinated contrast administration in patients with eGFR <60 or hepatic dysfunction and held for 48 hours until stable renal function is documented.
- Systematic 12-lead ECG analysis follows an invariant sequence: Rate, Rhythm, Axis, Intervals (PR, QRS, QTc), Chamber Enlargement, and Ischemia/Infarction localization across coronary anatomical distributions.
- Acute STEMI patterns correlate with coronary anatomy: Inferior (II, III, aVF = RCA; requires right-sided V4R lead check and avoidance of nitrates if RV involved); Anterior/Septal (V1-V4 = LAD); Lateral (I, aVL, V5, V6 = LCx/LAD). Wellens syndrome (biphasic/deeply inverted T waves in V2-V3) indicates critical proximal LAD stenosis.
- Pulmonary Function Testing (PFT) follows a 5-step sequence: Step 1 FEV1/FVC <0.70 confirms airflow obstruction; Step 2 assess FEV1 severity (GOLD 1-4); Step 3 test bronchodilator reversibility (ΔFEV1/FVC >12% and >200 mL); Step 4 if FEV1/FVC normal and FVC low, verify restriction via plethysmography (TLC <80%); Step 5 evaluate DLCO to distinguish emphysema/ILD (low DLCO) from asthma/chest wall restriction (normal DLCO).
Last updated: August 2026
Diagnostic Imaging, ECG Interpretation & Pulmonary Function Testing
Advanced clinical interpretation requires the AGPCNP to integrate multimodal structural, electrical, and physiological diagnostics. Mastering the indications, contraindications, systematic interpretation frameworks, and critical clinical pearls of diagnostic imaging, 12-lead electrocardiography (ECG), and pulmonary function testing (PFT) is paramount for competent adult-gerontology practice and board examination excellence.
1. Systematic Diagnostic Imaging Selection & Contrast Safety
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| DIAGNOSTIC IMAGING SELECTION MATRIX |
| |
| MODALITY PRIMARY INDICATIONS SAFETY / CONTRAINDICATIONS|
| +--------------------+ +--------------------------+ +--------------------+|
| | Non-Contrast CT | | Acute stroke, intracranial| | Avoid in pregnancy; ||
| | Head / Spine | | hemorrhage, head trauma, | | high cumulative ||
| | | | renal colic (calculi) | | radiation dose. ||
| +--------------------+ +--------------------------+ +--------------------+|
| | IV Contrast- | | Pulmonary embolism (CTPA)| | Check eGFR (<30 ml);||
| | Enhanced CT | | Acute abdomen, dissection| | Hold metformin 48h;||
| | (Iodinated) | | Bowel perforation/abscess| | Premedicate allergy.||
| +--------------------+ +--------------------------+ +--------------------+|
| | MRI / MRA | | Ischemic stroke (DWI), | | Pacemakers/ICDs, ||
| | (Gadolinium) | | Spinal cord compression, | | metallic implants; ||
| | | | soft tissue tumors, MS | | GFR <30 (NSF risk). ||
| +--------------------+ +--------------------------+ +--------------------+|
| | Ultrasound / | | Cholecystitis, DVT duplex| | Operator dependent; ||
| | POCUS / Echo | | AAA screen, pelvic mass | | safe in pregnancy; ||
| | | | Heart failure / EF% | | zero radiation. ||
| +--------------------+ +--------------------------+ +--------------------+|
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Systematic Chest Radiography (CXR): The ABCDEF Approach
When analyzing a standard Posteroanterior (PA) and Lateral CXR, execute an invariant reading algorithm:
- A — Airway: Trachea midline vs. shifted (shifted toward atelectasis/pneumonectomy; shifted away from tension pneumothorax or large pleural effusion); carina angle (<90°); visible mainstem bronchi.
- B — Bones & Soft Tissues: Clavicles, ribs (posterior rib fractures, lytic lesions in multiple myeloma), cervical spine, subcutaneous emphysema (crepitus/gas streaks in neck/chest wall from esophageal or bronchial rupture).
- C — Cardiac Silhouette & Mediastinum: Cardiothoracic ratio on PA view ($>0.50$ indicates cardiomegaly); aortic arch contour; mediastinal width ($>8$ cm at superior mediastinum suggests thoracic aortic dissection or mediastinitis).
- D — Diaphragm & Costophrenic Angles: Sharp, acute costophrenic angles (blunting requires $\ge 175$ mL fluid on PA view, $\ge 50$ mL on lateral view); hemi-diaphragm contour (right hemi-diaphragm sits $1-2$ cm higher than left due to liver); free air under diaphragm (pneumoperitoneum indicating hollow viscus perforation).
- E — Effusions & Extrathoracic Structures: Meniscus sign (pleural effusion); gastric air bubble location; surgical clips, pacemaker leads, PICC line tip placement (caval-atrial junction).
- F — Fields of the Lungs: Inspect symmetry across upper, middle, and lower zones. Silhouette sign (loss of normal anatomical margin):
- Loss of right heart border = Right Middle Lobe consolidation.
- Loss of left heart border = Lingular consolidation.
- Loss of hemi-diaphragm = Lower Lobe consolidation.
- Air Bronchograms (tubular lucencies of air-filled bronchi surrounded by fluid-filled alveoli) confirm alveolar consolidation (pneumonia or non-cardiogenic pulmonary edema).
- Kerley B Lines (horizontal 1–2 cm peripheral lines at lung bases touching pleura) indicate interstitial pulmonary edema and elevated pulmonary capillary wedge pressure.
Iodinated Contrast Protocols & Metformin Stewardship
- Contrast-Induced Nephropathy (CIN) Prevention: CIN is defined as an absolute increase in serum creatinine of $\ge 0.5$ mg/dL or a relative increase of $\ge 25%$ from baseline within 48–72 hours following iodinated contrast administration.
- High-Risk Threshold: Baseline eGFR $<30$ mL/min/1.73m$^2$, active diabetic nephropathy, congestive heart failure, dehydration.
- Evidence-Based Prevention: Intravenous volume expansion with isotonic crystalloids (0.9% Normal Saline at 1.0–1.5 mL/kg/hr for 3–12 hours pre-procedure and 6–12 hours post-procedure). Routine prophylactic N-acetylcysteine or sodium bicarbonate is no longer superior to isotonic saline alone.
- Metformin Protocol with Iodinated Contrast:
- Metformin does not cause renal failure, but if contrast induces acute renal failure, metformin accumulates, precipitating fatal Metformin-Associated Lactic Acidosis (MALA).
- Action Rule: In patients with baseline eGFR $<60$ mL/min/1.73m$^2$, hepatic dysfunction, or undergoing arterial catheterization, withhold Metformin at the time of contrast administration, hold for 48 hours post-procedure, and resume only after documenting stable renal function via repeat serum creatinine/eGFR.
- Contrast Allergy Premedication Regimen (Elective):
- Oral Prednisone 50 mg at 13 hours, 7 hours, and 1 hour prior to contrast injection, plus Diphenhydramine 50 mg IV/oral 1 hour prior.
2. Systematic 12-Lead Electrocardiogram (ECG) Interpretation
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| INVARIANT 6-STEP ECG ALGORITHM |
| |
| 1. RATE ---> 300-150-100-75-60-50 method or (QRS in 6 sec) x 10 |
| 2. RHYTHM ---> Sinus P waves (upright I, II, aVF; inverted aVR)? |
| 3. AXIS ---> Lead I and aVF Quadrant Method |
| 4. INTERVALS ---> PR (120-200ms), QRS (<120ms), QTc (<440ms M, <460ms F)|
| 5. HYPERTROPHY ---> LVH (Sokolow-Lyon: S in V1 + R in V5/V6 >= 35 mm) |
| 6. ISCHEMIA ---> ST Elevation / Depression, T wave inversion, Q waves |
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Mean QRS Electrical Axis Determination
+-----------------------------------------------------------------------------+
| QUADRANT AXIS DETERMINATION |
| |
| LEAD I NET QRS LEAD aVF NET QRS ELECTRICAL AXIS CLASSIFICATION|
| + (Positive) + (Positive) NORMAL AXIS (-30° to +90°) |
| + (Positive) - (Negative) Check Lead II: |
| - If II is +, Normal Axis |
| - If II is -, LEFT AXIS (-30° to -90°)|
| - (Negative) + (Positive) RIGHT AXIS DEVIATION (+90° to +180°)|
| - (Negative) - (Negative) EXTREME AXIS / "NORTHWEST" |
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Coronary Artery Territory & Ischemia Localization
| Anatomical Cardiac Region | Involved ECG Leads | Culprit Coronary Artery | Reciprocal ST Depression Leads | Critical Clinical Pearls |
|---|---|---|---|---|
| Inferior Wall | II, III, aVF | Right Coronary Artery (RCA) (~85%) or Left Circumflex (LCx) (~15%) | Leads I, aVL | • Check right-sided precordial leads (V3R, V4R) for Right Ventricular Infarction.<br>• Avoid Nitrates, Morphine, and Diuretics in RV infarction (patient is preload-dependent; nitrates trigger catastrophic hypotension). Treat hypotension with IV saline boluses.<br>• High risk of sinus bradycardia and high-grade AV block (RCA supplies SA and AV nodes). |
| Septal Wall | V1, V2 | Left Anterior Descending (LAD) (Septal perforators) | None | Associated with Bundle Branch Blocks and intraventricular conduction delays. |
| Anterior Wall | V3, V4 | Left Anterior Descending (LAD) ("Widow-maker") | Inferior leads (II, III, aVF) | High risk of cardiogenic shock, acute pulmonary edema, ventricular free wall rupture, and ventricular tachycardia. |
| Lateral Wall | I, aVL, V5, V6 | Left Circumflex (LCx) or Diagonal branch of LAD | Inferior leads (II, III, aVF) | High lateral (I, aVL) vs. Low lateral (V5, V6). |
| Posterior Wall | V7, V8, V9 (ST elevation $\ge 0.5$ mm) | RCA or LCx (Posterior descending) | V1, V2, V3 (Horizontal ST depression, tall broad R waves [R/S ratio >1], upright prominent T waves) | True posterior STEMI is frequently missed because standard 12-lead shows "mirror image" ST depressions in V1-V3. Obtain posterior leads (V7-V9). |
+-----------------------------------------------------------------------------+
| HIGH-RISK ECG PATTERNS & STEMI EQUIVALENTS |
| |
| WELLENS SYNDROME TYPE A ---> Biphasic T waves in V2-V3 |
| WELLENS SYNDROME TYPE B ---> Deeply inverted symmetric T waves in V2-V3 |
| Significance: Critical proximal LAD stenosis|
| Action: Urgent cath; STRESS TEST CONTRAINDICATED!|
| |
| de WINTER T WAVES ---> 1-3 mm upsloping ST depression at J-point |
| followed by tall, prominent, symmetric T |
| waves in V1-V6. (Acute LAD occlusion). |
| |
| ACUTE PERICARDITIS ---> Diffuse, concave-upward ST elevation across|
| all leads (I, II, aVF, V2-V6) + PR DEPRESSION.|
| Lead aVR shows PR ELEVATION and ST DEPRESSION.|
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Atrioventricular (AV) Blocks & Bundle Branch Blocks
+-----------------------------------------------------------------------------+
| ATRIOVENTRICULAR (AV) BLOCK TAXONOMY |
| |
| FIRST-DEGREE AV BLOCK ---> PR interval > 200 ms (>5 small boxes); |
| every P wave is followed by a QRS (1:1). |
| |
| SECOND-DEGREE MOBITZ I ---> Progressive PR prolongation until a QRS is |
| (WENCKEBACH) dropped ("Longer, longer, longer, drop!"). |
| Pathology: AV Node. Usually benign/stable. |
| |
| SECOND-DEGREE MOBITZ II ---> Constant, fixed PR interval with intermittent|
| dropped QRS complexes without warning. |
| Pathology: His-Purkinje. HIGH RISK OF CHB! |
| Action: Pacemaker required. |
| |
| THIRD-DEGREE (COMPLETE) ---> Complete AV dissociation; P waves and QRS |
| HEART BLOCK beat independently (PP regular, RR regular).|
| Action: Emergent transcutaneous/transvenous |
| pacing; permanent pacemaker implantation. |
+-----------------------------------------------------------------------------+
- Left Bundle Branch Block (LBBB): QRS duration $\ge 120$ ms (3 small boxes); broad, notched, or slurred R waves in lateral leads (I, aVL, V5, V6); deep, broad S waves in V1-V2; absence of septal Q waves in lateral leads.
- Sgarbossa Criteria for MI in pre-existing LBBB: Concordant ST elevation $\ge 1$ mm in leads with positive QRS (5 pts); Concordant ST depression $\ge 1$ mm in leads V1-V3 (3 pts); Proportionally excessive discordant ST elevation $\ge 25%$ of the depth of the preceding S wave (2 pts). Score $\ge 3$ indicates acute STEMI.
- Right Bundle Branch Block (RBBB): QRS duration $\ge 120$ ms; $RSR'$ ("rabbit ears") in leads V1-V2; wide, slurred S wave in lateral leads (I, aVL, V6).
3. Pulmonary Function Testing (PFT) & Spirometry Interpretation
Spirometry and complete pulmonary function testing provide essential physiological data to diagnose, stage, and monitor respiratory diseases.
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| STEPWISE PFT INTERPRETATION ALGORITHM |
| |
| [STEP 1: CHECK FEV1 / FVC RATIO] |
| | |
| +-----------------------------------+-------------------------------+ |
| | | |
| v v |
| [RATIO <0.70 (or <LLN)] [RATIO >= 0.70 (Normal)]|
| OBSTRUCTIVE VENTILATORY DEFECT Check FVC (% predicted)|
| | | |
| v +---------------+---------------+ |
| [STEP 2: ASSESS SEVERITY (FEV1 %)] | | |
| - GOLD 1 (Mild): FEV1 >= 80% v v |
| - GOLD 2 (Moderate): FEV1 50-79% [FVC >= 80% (Normal)] [FVC < 80% (Reduced)]|
| - GOLD 3 (Severe): FEV1 30-49% NORMAL SPIROMETRY SUSPECT RESTRICTIVE PATTERN|
| - GOLD 4 (Very Severe): FEV1 < 30% | | |
| | v v |
| v [CHECK DLCO] [STEP 4: PLETHYSMOGRAPHY]|
| [STEP 3: BRONCHODILATOR REVERSIBILITY] - Normal: Healthy Check Total Lung Capacity (TLC)
| Administer 4 puffs Albuterol; retest. - Low: Early ILD, - TLC < 80%: CONFIRMED RESTRICTION|
| Significant if: Pulmonary HTN, - TLC >= 80%: Air trapping / normal|
| - FEV1 or FVC increases by >12% AND >200 mL severe Anemia | |
| - Positive = Asthma (or Asthma-COPD overlap) v |
| - Negative / Fixed = COPD [STEP 5: EVALUATE DLCO]|
| | | |
| +-----------------------------------------------------------------------------------+ |
| | |
| v |
| [STEP 5: DIFFUSING CAPACITY (DLCO)] |
| | |
| +-----------------------------------+-----------------------------------+ |
| | | |
| v v |
| [REDUCED DLCO (<80% predicted)] [NORMAL OR ELEVATED DLCO (>=80%)] |
| - Obstructive + Low DLCO = EMPHYSEMA - Obstructive + Normal DLCO = ASTHMA|
| - Restrictive + Low DLCO = INTRINSIC PARENCHYMAL ILD or CHRONIC BRONCHITIS |
| (Idiopathic Pulmonary Fibrosis, Sarcoidosis, - Restrictive + Normal DLCO = |
| Asbestosis, Amiodarone toxicity) EXTRINSIC / CHEST WALL / NEUROMUSCULAR|
| - Isolated Low DLCO with normal spirometry = (Obesity hypoventilation, Scoliosis,|
| Pulmonary Arterial Hypertension or CTEPH Myasthenia Gravis, ALS, Guillain-Barré)|
+-----------------------------------------------------------------------------+
Comprehensive Spirometry & DLCO Differentiation Matrix
| Diagnostic Classification | FEV1/FVC Ratio | FVC (% pred) | FEV1 (% pred) | Bronchodilator Reversibility | TLC (% pred) | DLCO (% pred) | Hallmark Clinical Conditions |
|---|---|---|---|---|---|---|---|
| Asthma | Reduced (<0.70) | Normal or Reduced | Reduced | Positive ($>12%$ and $>200$ mL) | Normal or Elevated | Normal or Elevated ($>100%$) | Bronchial hyperreactivity, atopy, episodic wheezing, triggers. |
| COPD: Emphysema | Reduced (<0.70) | Normal or Reduced | Reduced | Negative (or minimal/fixed) | Elevated ($>120%$, hyperinflation) | Reduced (<80%) | Alveolar-capillary membrane destruction, loss of elastic recoil, tobacco history. |
| COPD: Chronic Bronchitis | Reduced (<0.70) | Normal or Reduced | Reduced | Negative (or minimal/fixed) | Normal | Normal or Mildly Reduced | Chronic productive cough for $\ge 3$ consecutive months in 2 consecutive years. |
| Intrinsic Restrictive (ILD / IPF) | Normal or High ($>0.75$) | Reduced (<80%) | Reduced | Negative | Reduced (<80%) | Markedly Reduced (<60%) | Idiopathic pulmonary fibrosis, sarcoidosis, hypersensitivity pneumonitis, drug toxicity (amiodarone, bleomycin, nitrofurantoin). |
| Extrinsic Restrictive (Chest Wall / Neuromuscular) | Normal or High ($>0.75$) | Reduced (<80%) | Reduced | Negative | Reduced (<80%) | NORMAL ($\ge 80%$) | Severe kyphoscoliosis, morbid obesity hypoventilation syndrome, ALS, myasthenia gravis, diaphragmatic paralysis. |
| Pulmonary Vascular Disease | Normal ($\ge 0.70$) | Normal ($\ge 80%$) | Normal ($\ge 80%$) | Negative | Normal ($\ge 80%$) | Isolated Reduction (<80%) | Pulmonary Arterial Hypertension (PAH), Chronic Thromboembolic Pulmonary Hypertension (CTEPH), severe anemia. |
Test Your Knowledge
A 64-year-old male with a history of hypertension, hyperlipidemia, and a 40 pack-year smoking history is brought to the clinic reporting sudden, severe, substernal crushing chest pressure that began 45 minutes ago while shoveling snow. He is diaphoretic, pale, and nauseated. Vital signs: BP 92/58 mmHg, HR 54 bpm (sinus bradycardia), RR 20/min, and SpO2 96% on room air. An immediate 12-lead ECG demonstrates 2.5 mm ST-segment elevation in leads II, III, and aVF with 1.5 mm ST-segment depression in leads I and aVL. Which clinical action is the most appropriate next step in acute management?
A
B
C
D
Test Your Knowledge
An AGPCNP is interpreting pulmonary function tests for a 58-year-old male former smoker presenting with progressive exertional dyspnea and chronic dry cough. The report reveals: Post-bronchodilator FEV1/FVC ratio is 0.78 (normal >0.70); FVC is 54% of predicted (severely reduced); FEV1 is 56% of predicted; Total Lung Capacity (TLC) measured by body plethysmography is 62% of predicted; and Diffusing Capacity of the Lung for Carbon Monoxide (DLCO) is 42% of predicted (severely reduced). Which underlying pathology is most consistent with this pattern?
A
B
C
D
Test Your Knowledge
A 42-year-old female with no significant medical history presents to the urgent care clinic with sudden-onset, sharp, right-sided pleuritic chest pain and dyspnea that began 3 hours ago after returning from an 11-hour transatlantic flight. She takes an oral combined ethinyl estradiol/levonorgestrel contraceptive pill. Vital signs: BP 124/78 mmHg, HR 112 bpm (sinus tachycardia), RR 24/min, SpO2 93% on room air, and temperature 37.1°C (98.8°F). Physical examination of the chest reveals clear, vesicular breath sounds bilaterally. Two-view chest radiography is completely normal. What is the gold-standard diagnostic imaging study required to establish a definitive diagnosis?
A
B
C
D