Hypotension and Near-syncope in a 66-year-old Woman

A 66-year-old woman presents to the ED with a 3-day history of generalized weakness, malaise, recurrent near-syncope, nausea, and occasional vomiting. She denies chest pain, fever, difficulty breathing, diarrhea, and fainting. Her history includes diabetes, end-stage renal disease, coronary disease, and complete heart block after pacemaker implantation.

She is afebrile. Pulse is 126 beats/min; blood pressure, 81/53 mm Hg; and oxygen saturation, 100% on room air. She appears adequately hydrated as evidenced by a moist oropharynx. There is no jugular venous distention or thyroid mass. Heart rate is regular and rapid without murmur, and lungs are clear. She has weak peripheral pulses and mild bilateral pitting edema, which she states is of recent onset. Other physical findings are unremarkable.

Laboratory results, including a CBC count, metabolic panel, and troponin I level, are normal. Urinalysis shows 25 white blood cells per high-power field with few bacteria.

Her ECG is shown below.

What is your ECG read?

Answer and discussion on next page>>

Answer: Pacemaker-mediated tachycardia

Antibiotic treatment was initiated for possible urosepsis despite the lack of fever and leukocytosis. Although there was no clear evidence of dehydration, IV fluids were administered because of the hypotension, history of vomiting, and possible sepsis. When the patient’s blood pressure remained unchanged, pacemaker interrogation was expedited for possible pacemaker-mediated tachycardia (PMT), which turned out to be the correct diagnosis. The unit was reprogrammed, and all vital signs immediately normalized.

A second ECG is shown below.

Discussion

Pacemaker-mediated tachycardia (PMT) is rare, especially with modern pacemakers, in which a perpetual activation loop occurs between the atrial and ventricular leads. The ventricular rate is typically under 130 beats/min, which represents the upper programmed set rate limit of the pacemaker. Nevertheless, hemodynamic compromise, namely hypotension, may still occur. As in this case, PMT is often not considered until other, more common conditions have been ruled out and no other explanation seems plausible.

Symptoms typically include generalized weakness and syncope or near-syncope. Palpitations and chest pain may occur. Blood pressure is often low, and the pulse is typically between 110 and 130 beats/min. Neither hypotension nor tachycardia is usually responsive to fluids in patients with PMT, which is one clue to the diagnosis.

Once the diagnosis of PMT is suspected, a cardiologist should be consulted and a representative from the pacemaker company called to interrogate the pacer. Pacer interrogation can confirm the diagnosis and can be followed by pacer reprogramming to terminate the tachycardia. If the patient is unstable, application of a magnet to the pacemaker should break PMT by switching to a non-synchronous present rate (usually between 60 and 100 beats/min). If a magnet is not available, atrioventricular nodal blockers can be tried, but caution should be used if the diagnosis is uncertain because in other conditions they may worsen hypotension.

For more information on PMT, see the chart below.

Excerpt on PACEMAKER MEDIATED TACHYCARDIA (PMT) The Emergency Medicine 1-minute Consult Quick Essentials pocketbook