Intrathoracic Impedance (Dietary Incompliance)

Age	Gender	Occupation	Working Diagnosis
65 Years	Male	Businessman	OptiVol Alert for Fluid Overload

History

In August 2008 the patient received a biventricular implantable cardioverter-defibrillator (ICD; Concerto, Medtronic, Minneapolis, Minn.) due to dilated cardiomyopathy with symptomatic heart failure (New York Heart Association [NYHA] class III) despite optimal pharmacologic treatment. Before implantation, his left ventricular ejection fraction (LVEF) was 20%, with a pattern of global hypokinesia. He was in permanent atrial fibrillation, and the surface electrocardiogram (ECG) showed a typical left bundle branch block and QRS duration of 160 ms. After 6 months of cardiac resynchronization therapy (CRT), he had improved to NYHA class II and the LVEF had increased to 35%.

The device collected daily information about intrathoracic impedance and tracked changes in the OptiVol Fluid Index. Intrathoracic impedance can be measured between a right ventricular pacing or defibrillation lead and the device can. Impedance decreases with an increase in blood volume and pulmonary fluid content. The OptiVol fluid index compares the actual patient impedance with a reference impedance derived from a moving average algorithm. When daily impedance falls below the reference, the difference accumulates in the OptiVol Fluid Index. If the OptiVol Fluid Index crosses a certain threshold, an alert can be triggered indicating that the patient is at increased risk for subsequent heart failure decompensation. This may facilitate timely therapeutic interventions. A threshold crossing incident can be indicated to the patient by an audible tone from the device (OptiVol alert) or to the heart failure team by means of remote patient monitoring.

The patient was enrolled in a clinical study. According to the protocol, he was not connected to remote patient monitoring and the OptiVol alert was programmed “on.”

Comments

The patient fulfilled essential guideline criteria for implantation of a CRT defibrillator (CRT-D) system. At the time of implantation, the role of CRT in patients with atrial fibrillation was unclear. Nevertheless, implantation of a CRT-D system in a patient such as this reflected common clinical practice. As a result of the beneficial clinical course and improvements in left ventricular function after 6 months, he was considered a responder to CRT treatment.

Current Medications

The patient was taking warfarin (INR 2-3), bisoprolol 10 mg daily, enalapril 20 mg daily, spironolactone 25 mg daily, digoxin 0.25 mg daily, and furosemide 40 mg twice daily.

Comments

The medication regimen represents current guideline recommendations. During treatment with bisoprolol and digoxin the spontaneous heart rate was constantly below the basic paced heart rate of 70 bpm (VVIR mode). The proportion of biventricular stimulation was above 98%. Therefore atrioventricular junctional ablation was not deemed necessary.

Current Symptoms

On August 23, 2009, the patient participated in a crayfish party, which is a traditional eating and drinking celebration in the Nordic countries held in late summer during the legal crayfish harvesting period. A crayfish dinner is typically associated with intake of large amounts of salt, and alcohol consumption (with snaps, the Swedish for small shots of strong alcohol) may be high. These deviations from essential dietary restrictions prudent for heart failure patients are usually followed by increased water consumption.

During the next several days, a fall in impedance and an increase in the OptiVol Fluid Index was observed. On September 9, the Fluid Index threshold of 60 Ohm∗days was crossed and the audible OptiVol alert was activated every morning as long as the Fluid Index remained above threshold values. The patient had been instructed to contact his heart failure clinic in case of an OptiVol alert. Despite this, he waited 12 more days before calling the clinic. Being a well-educated patient, he suspected a causal relationship between the dietary incompliance and the consecutive fluid alert. In fact, he later reported transient symptoms of minor weight increase, dyspnea, and slight ankle swelling for a few days after the dinner. During the last week before contacting the clinic, he took an extra tablet of furosemide 40 mg daily.

On September 10 the patient was seen at the heart failure clinic. At this time, symptoms had disappeared and body weight had normalized. The physical status revealed no sign of overt fluid overload. Information about intrathoracic impedance was read from the device memory. Notably, impedance had increased again for some days and was about to cross the line of the reference impedance. This was consistent with normalization of heart failure signs and symptoms and indicated that the audible alert would soon disappear. It was recommended that the patient continue with his ordinary medical prescription. The patient was reminded about restrictions concerning salt, fluid, and alcohol intake. Flexible use of diuretics in response to subjective signs and symptoms of heart failure was encouraged.

On October 8 a control visit was made. The patient’s condition remained unchanged. Device interrogation showed that the OptiVol Fluid Index had normalized soon after the prior visit and impedance had returned to a level indicating normal fluid conditions.

Comments

The patient was asymptomatic at the examination, and the alert could be regarded as a false alert. However, the patient’s history indicated transient heart failure deterioration as the most probable explanation. Dietary incompliance can lead to fluid retention and is often involved in heart failure decompensation.

In the present case, the patient had already taken therapeutic action by increasing the dose of diuretics and any additional impact of the clinician encounter cannot be proved. However, during the patient visit the pathophysiologic mechanism of the event was confirmed and important educational advice was provided.

Patient–clinician interaction in a case such as this should rather be established using remote monitoring technology. A phone call together with a remote check of other device diagnostics (i.e., heart rate, heart rate variability, physical activity, ventricular arrhythmia burden, and percentage biventricular pacing, all of which were normal in the present case) would likely be sufficient to resolve this situation without the need for an office visit.

The value of audible alerts has been disputed. In the randomized Diagnostic Outcome Trial in Heart Failure trial, patients in whom the audible alert was activated had a higher incidence of hospitalizations for heart failure. Obviously, audible alerts can trigger patient and physician concerns and thereby lower the threshold for hospitalization. Still, other studies have demonstrated that fluid alerts should direct the attention of clinicians to an increased risk for heart failure–related events. Trials evaluating the concept of impedance monitoring in the context of remote patient monitoring are under way.

Physical Examination

BP/HR: 110/80 mm Hg/70 bpm (regular)
Height/weight: 192 cm/93 kg
Neck veins: Normal
Lungs/chest: Clear
Heart: Apical systolic murmur (grade 1/6)
Abdomen: Normal status
Extremities: No peripheral edema

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