ECG Challenge: A 67-year-old man with prostate cancer currently being treated with radiation therapy presents to the hospital with complaints of inability to urinate for the past 2 days. It is noted that he is obstructed, and a Foley catheter is inserted with difficulty. Several hours later, the patient develops shaking chills and diaphoresis and has a blood pressure of 89/60 mm Hg. It is felt that he has urosepsis and is started on antibiotics and pressors for early septic shock. As a result, he develops tachycardia, and an ECG (ECG A) is obtained. His temperature decreases, and his blood pressure increases to 120/80 mm Hg, at which time the pressors are discontinued. His heart rate is slower, and an ECG is repeated (ECG B).
ECG A shows a regular tachycardia at a rate of 160 bpm. One longer RR interval is seen. It also appears that there is a long RR interval at the beginning of the ECG (▲). The QRS complex is wide (0.12 second), and there is a morphology of a right bundle-branch block with a broad R wave in lead V1 (→), along with a broad terminal S wave in leads 1, V5, and V6 (←). The axis is normal between 0° and +90° (positive QRS complex in lead I when the terminal S wave is ignored and positive QRS complex in lead aVF). Low voltage is seen. This is defined as a QRS complex amplitude <5 mm in each limb lead and <10 mm in each precordial lead. Q waves are seen in leads II, III, and aVF (↑), consistent with an old inferior wall myocardial infarction. The QT/QTc intervals are normal (260/425 and 240/390 milliseconds when the prolonged QRS complex duration is considered). No apparent P waves are seen before or after the QRS complexes of the tachycardia. However, a P wave can be seen (+) before the QRS complex ending the 2 long RR intervals (o). The PR interval is 0.16 second. The QRS complex that follows the P wave (o) is narrow (0.08 second) with a normal morphology. This is therefore a sinus complex. There is a tall R wave in lead V2 (]), consistent with early transition or counterclockwise rotation of the electric axis in the horizontal plane. This is established by imagining the heart as viewed from under the diaphragm. With counterclockwise rotation, the left ventricular forces appear early in the precordial leads. Because the sinus QRS complex is narrow, the right bundle-branch block is rate related. After this narrow sinus complex (o), another P wave can be seen (*) that is followed by a QRS complex with a right bundle-branch block (▼). The PR interval (└┘) is longer (0.26 second) than the sinus PR interval despite a shorter RR interval (ie, faster rate). This is therefore not a sinus complex but an atrial complex that is the first complex of the tachycardia. There is a positive waveform at the end of the QRS complexes (v) of the tachycardia (best seen in lead V1 [v] and seen as notches in the ST segment in lead III and aVL [^]), and the interval between this waveform and the next QRS complex is identical (0.26 second) to the PR interval of the first QRS complex of the tachycardia (└┘). This PR interval is consistent thereafter. This positive waveform is therefore a P wave, and a short RP tachycardia is present. Because this begins with a premature P wave and QRS complex that has the same PR interval, the most likely diagnosis is an atrial tachycardia with 1:1 atrioventricular conduction.
ECG B shows a regular rhythm at a rate of 95 bpm. The QRS complex is narrow (0.08 second) and has a morphology that is the same as that of the narrow complexes in ECG A. The QT/QTc intervals are normal (360/450 milliseconds). Nonspecific T-wave abnormalities are present (^). P waves can be seen, especially in lead V1 (v). The PP interval is regular, and the atrial rate is 200 bpm, which is identical to the ventricular and atrial rates of the tachycardia in ECG A. Therefore, this is an atrial tachycardia with 2:1 atrioventricular block.
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