CCT (CCI) cheat sheet

Standard 12-lead electrode positions: V1 in the fourth intercostal space at the right sternal border; V2 at the left sternal border; V3 midway between V2 and V4; V4 in the fifth intercostal space at the midclavicular line; V5 at the anterior axillary line; V6 at the midaxillary line.

At 25 mm/s and 10 mm/mV, one small box is 0.04 s (40 ms) and one large box is 0.20 s (200 ms); a 1 mV signal produces a 10 mm vertical deflection.

Skin preparation: clip excessive hair, lightly abrade, clean with alcohol, and let dry; lotion, sweat, and poor adhesion increase baseline wander and 60-Hz artifact.

Left arm/right arm lead reversal: lead I is inverted, aVR and aVL are exchanged, and leads II and III are exchanged; this can falsely suggest inferior infarction or right axis deviation.

Orthostatic vital signs: measure after 5 minutes supine and at 1 and 3 minutes standing; a systolic drop of at least 20 mm Hg or diastolic drop of at least 10 mm Hg is diagnostic.

Blood pressure cuff selection: bladder length about 80% of arm circumference and width about 40% of arm length; a cuff that is too small falsely raises the reading.

Patient identification and privacy: verify two identifiers, explain the procedure, obtain consent where required, and expose only the necessary chest area.

Emergency readiness: know the location of the defibrillator, oxygen, and suction; stop the procedure if the patient develops chest pain, syncope, or severe dyspnea.

Heart rate: for regular rhythms divide 300 by the number of large boxes between R waves; for irregular rhythms count QRS complexes in 10 seconds and multiply by 6.

Normal intervals: PR 0.12 to 0.20 s, QRS less than 0.12 s, and QTc generally less than 0.44 s in men and less than 0.46 s in women.

Axis from leads I and aVF: both positive is normal; I positive with aVF negative is left axis; I negative with aVF positive is right axis; both negative is extreme axis.

Left bundle branch block: QRS at least 0.12 s, broad notched R waves in I, aVL, V5, and V6, and QS or rS complexes in V1.

Right bundle branch block: QRS at least 0.12 s with an rSR prime pattern in V1 and a wide slurred S wave in leads I and V6.

LVH voltage: Sokolow-Lyon S in V1 plus R in V5 or V6 at least 35 mm; Cornell R in aVL plus S in V3 greater than 28 mm in men and greater than 20 mm in women.

STEMI territories: II, III, and aVF indicate inferior injury; V1 to V4 indicate anterior injury; I, aVL, V5, and V6 indicate lateral injury; V7 to V9 indicate posterior injury.

QTc by Bazett formula: QTc equals the measured QT interval divided by the square root of the RR interval, with both intervals expressed in seconds.

Sinus rhythm criteria: upright P wave in lead II, rate 60 to 100 per minute, constant PR interval, and every P wave followed by a QRS complex.

Atrial fibrillation: irregularly irregular ventricular response, absent P waves, and fibrillatory baseline activity; AF burden influences anticoagulation and rate-control decisions.

Atrial flutter: sawtooth flutter waves with an atrial rate near 250 to 350 per minute; 2:1 conduction produces a ventricular rate near 150 per minute.

Supraventricular tachycardia: narrow-complex regular tachycardia at 150 to 250 per minute with abrupt onset and offset; P waves are often hidden in the QRS or T wave.

Ventricular tachycardia: wide QRS greater than 0.12 s at a rate above 100 per minute, often with AV dissociation, fusion beats, or capture beats.

First-degree AV block: PR interval longer than 0.20 s with every P wave conducted; Mobitz I shows progressive PR prolongation before a dropped QRS; Mobitz II shows a constant PR with dropped QRS complexes.

Third-degree AV block: P waves and QRS complexes are independent; a junctional escape rhythm is 40 to 60 per minute and an idioventricular escape rhythm is 20 to 40 per minute.

Premature ventricular complex: premature wide QRS with no preceding P wave, discordant T wave, and often a full compensatory pause.

Junctional rhythm: narrow QRS at 40 to 60 per minute with an inverted, absent, or retrograde P wave; accelerated junctional rhythm is 60 to 100 per minute.

Holter monitoring: continuous ECG recording for 24 to 48 hours, typically with 3 to 12 leads, while the patient keeps a symptom and activity diary.

Event monitoring: intermittent recording over weeks to months, activated by the patient or automatically, for infrequent palpitations, syncope, or suspected AF.

Implantable loop recorder: a subcutaneous device that continuously monitors for years and auto-detects pauses, bradycardia, tachycardia, and atrial fibrillation.

Patient instructions: maintain a symptom diary, avoid showering with a Holter monitor, keep mobile phones away from cables, and record activity at the time of symptoms.

Electrode preparation: clip hair, gently abrade the skin, clean with alcohol, and place leads over bone rather than muscle to reduce movement and muscle artifact.

Common artifact sources: tooth brushing, tapping the device, cable movement, and muscle tremor; compare channels and the diary before interpreting an apparent arrhythmia.

Significant findings: pauses longer than 3 seconds, sustained SVT or VT, high atrial fibrillation burden, and extreme rate excursions should be correlated with symptoms.

Analysis workflow: review heart-rate trends, ST segments, arrhythmia burden, and symptom-rhythm correlation; manual overread confirms automated arrhythmia calls.

Bruce protocol stages are 3 minutes each: stage 1 is 1.7 mph at 10% grade, stage 2 is 2.5 mph at 12%, stage 3 is 3.4 mph at 14%, and stage 4 is 4.2 mph at 16%.

Target heart rate: estimated maximum heart rate is 220 minus age; a diagnostic test commonly targets at least 85% of this predicted value.

Positive exercise ECG criterion: at least 1 mm of horizontal or downsloping ST depression measured 80 ms after the J point in two or more contiguous leads.

Exercise endpoints: achievement of target heart rate, marked ST depression, chest pain, systolic blood pressure fall greater than 10 mm Hg, serious arrhythmia, severe dyspnea, or fatigue.

Contraindications: acute myocardial infarction, unstable angina, uncontrolled hypertension above 200/110 mm Hg, severe aortic stenosis, uncontrolled arrhythmia, and acute pulmonary embolism.

Blood pressure response: systolic pressure normally rises with workload; a fall greater than 10 mm Hg from baseline or failure to rise suggests severe ischemia or left ventricular dysfunction.

Recovery monitoring: observe ECG and blood pressure for at least 6 to 10 minutes after exercise because ischemic ST changes and arrhythmias may appear only during recovery.

Safety readiness: crash cart, defibrillator, oxygen, suction, intravenous access, and trained staff must be immediately available during exercise stress testing.