Electrophysiology Procedure Planning: Using Nuclear Modalities to Help Guide Ablations & Patient Selection
Due to the commonality of these arrhythmias and the number of procedures necessary to treat them, there is a growing need for the field of electrophysiology (EP). And to better treat patients with dangerous arrhythmias, practitioners have begun using cardiac PET and SPECT to help in patient selection and to guide EP procedures including ablations, lead placements and CRT implantations.
Researchers at the Leiden University Medical Center in Leiden, the Netherlands, have begun using myocardial perfusion SPECT to assess left ventricular (LV) end-systolic volume, LV end-diastolic volume and LV ejection fraction (LVEF) in advanced heart failure (HF) patients who were to be implanted with cardiac resynchronization therapy (CRT) [J Nucl Med Mol Imaging, online Oct. 17, 2010].
Because the assessment of cardiac function is an important issue in patients with LV dysfunction, and adding SPECT into the mix can help improve test specificity and better characterize functional abnormalities. In addition, evaluating LV volumes via SPECT can help physicians determine the correct and most appropriate management strategy.
“In these types of cases, nuclear cardiac imaging is able to provide a tailored, more patient-specific treatment approach,” says Timm Dickfeld, MD, PhD, an associate professor of medicine at University of Maryland, Baltimore. In the case of ablation, prior knowledge of scar location can assist in planning of the ablation access and target signal acquisition during the case. “For CRT patient selection of a side branch stenosis in the viable myocardium, this can be advantageous over lead placement in areas of significant myocardial scar,” offers Dickfeld.
Others, like those at the University of Pittsburgh and the University of Maryland Medical Center (UMMC) in Baltimore, have followed suit and are now using nuclear imaging to help with patient selection and device placement for patients with arrhythmias.
Currently, a selection criterion for patients who may need resynchronization therapy is centered on three aspects: a low LV LVEF, HF symptoms and a wide QRS complex on the ECG, which is often a poor surrogate for mechanical dyssynchrony.
The research, presented at the 2010 American Society of Nuclear Cardiology (ASNC) meeting, won the Young Investigator Award Competition for its innovative approach using cardiac SPECT to assess mechanical synchrony of the LV before and immediately after CRT device activation.
SPECT can better detail LVEF information and outline whether or not the patient has some element of dyssynchrony, which could be improved by resynchronization, says Mati S. Friehling, MD, a cardiology fellow at UPitt.
The researchers enrolled 44 patients after CRT device implantation, but CRT devices were left inactive, unless the patient was pacemaker dependent. During the baseline scan, patients were injected with a single injection radiotracer (sestamibi). “The idea here was to see whether or not turning on the CRT device would make a change in a patients LV mechanical synchrony after the baseline scan,” says Friehling.
After the baseline exam, 18 patients had improved dyssynchrony, 11 had no change and 15 had a deterioration of dyssynchrony. Of the 29 patients who had improved or unchanged dyssynchrony, five deaths occurred, and of the 15 patients who experienced deterioration of dyssyncrony, eight experienced a cardiac event. Patients who were acutely desynchronized by CRT had higher rates of composite death, HF hospitalizations and ICD shocks, says Friehling.
And rather than injecting patients with a double-dose of radiotracer to perform a second SPECT exam, patients were scanned again within four hours of the baseline exam so the radiotracer was still present in the heart, says Friehling, avoiding a duplicate dose of radiation.
Once the second image set was acquired, “we could look at the LV mechanical and see whether the device was really resynchronizing the patient,” he says.
“We found a good number of patients who actually had a deterioration in their synchrony after the device was turned on and the implication of this was that these might be the patients who go on to have more heart failure or more ICD shocks and do worse over the long term if we put a device in that actually made them worse,” Friehling notes.
Friehling says these results may open many doors for the future of clinical practice and soon with just a baseline SPECT scan practitioners will be able to decide whether or not patients should receive a CRT device and how and where the ventricular lead should be placed.
“The reason why this would be helpful on all those fronts is because when you do a nuclear SPECT study you get a lot of information—perfusion data where you can see which parts of the LV are scarred, ejection fraction information so you can decipher if the patients even meet standard criteria for CRT and then the third thing is dyssynchrony information,” he says. “So using all of that information just from a baseline scan will allow us to improve our selection criteria.”
Currently, this is being used just as a research tool for CRT. But Friehling says, “Even just using the nuclear imaging scans to obtain a more accurate ejection fraction and a way of determining scar burden it is beneficial.”
In the future, he offers that this tactic may also be useful for patients being implanted with ICDs. “Because there are really strict cutoffs on which patients will benefit or who you should put an ICD in so if we are using modalities like echo the ejection fraction is highly variable I think that nuclear imaging might be a little better for something like that too.”
The researchers are using cardiac PET/SPECT imaging to derive 3D scar maps and create segmental analysis to help quantitatively compare EP voltages and PET/SPECT inferred tissue properties to ultimately help guide clinical VT ablations.
Dickfeld et al found that use of PET/SPECT accurately assesses LV scar and border zones and is a useful approach to understanding the scar characterization that may not be attained through EP voltage maps (J Am Coll Cardiol Img, 2008; 1:73-82).
The 3D reconstructions can allow for the scar border zone to be evaluated and also pinpoint exactly where the VT or VF is coming from, he says. To date, UMMC has imaged close to 50 patients with PET or SPECT prior to an ablation procedure.
“These fast heart rates need scarring to exist and persist,” says Dickfeld. “That is why we need to do scar imaging. We want to know exactly where that scar is and once we have our PET scan we try to qualitatively and quantitatively define where that scar is.
“We now have the ability to cut the heart into 720 little pieces and register the metabolic data from the PET exam to the voltage data we obtain during a procedure…so we can look at the areas where we can successfully terminate the arrhythmias,” says Dickfeld.
But, University of Maryland nuclear medicine physicist Mark Smith, PhD, says finding a common reference frame to actually compare the EP voltage values with quantitative or semi-quantitative values from the PET or SPECT exams is not all that easy.
However, his facility has developed tools to automate the analysis of the EP voltages and PET/SPECT data to help facilitate this process. The cardiac images are exported in DICOM format and then analyzed using a software program (PMOD Technologies) to retrospectively map the myocardium. These data are then exported and run through spreadsheets to quantify various tracers in the patient’s heart.
Researchers at the Leiden University Medical Center in Leiden, the Netherlands, have begun using myocardial perfusion SPECT to assess left ventricular (LV) end-systolic volume, LV end-diastolic volume and LV ejection fraction (LVEF) in advanced heart failure (HF) patients who were to be implanted with cardiac resynchronization therapy (CRT) [J Nucl Med Mol Imaging, online Oct. 17, 2010].
Because the assessment of cardiac function is an important issue in patients with LV dysfunction, and adding SPECT into the mix can help improve test specificity and better characterize functional abnormalities. In addition, evaluating LV volumes via SPECT can help physicians determine the correct and most appropriate management strategy.
“In these types of cases, nuclear cardiac imaging is able to provide a tailored, more patient-specific treatment approach,” says Timm Dickfeld, MD, PhD, an associate professor of medicine at University of Maryland, Baltimore. In the case of ablation, prior knowledge of scar location can assist in planning of the ablation access and target signal acquisition during the case. “For CRT patient selection of a side branch stenosis in the viable myocardium, this can be advantageous over lead placement in areas of significant myocardial scar,” offers Dickfeld.
Others, like those at the University of Pittsburgh and the University of Maryland Medical Center (UMMC) in Baltimore, have followed suit and are now using nuclear imaging to help with patient selection and device placement for patients with arrhythmias.
Guiding CRT patients selection with nuclear scans
Researchers at the University of Pittsburgh department of medicine have developed a research protocol using cardiac SPECT to help guide patient selection for CRT and LV lead placement.Currently, a selection criterion for patients who may need resynchronization therapy is centered on three aspects: a low LV LVEF, HF symptoms and a wide QRS complex on the ECG, which is often a poor surrogate for mechanical dyssynchrony.
The research, presented at the 2010 American Society of Nuclear Cardiology (ASNC) meeting, won the Young Investigator Award Competition for its innovative approach using cardiac SPECT to assess mechanical synchrony of the LV before and immediately after CRT device activation.
SPECT can better detail LVEF information and outline whether or not the patient has some element of dyssynchrony, which could be improved by resynchronization, says Mati S. Friehling, MD, a cardiology fellow at UPitt.
| Arrhythmias By the Numbers |
| The number of patients with cardiac arrhythmias—tachycardia, bradycardia, atrial fibrillation (AF), supraventricular tachycardia, ventricular tachycardia (VT), among others—is continuously growing. And while AF may be most common, affecting almost 2.2 million patients in the U.S., almost 300,000 Americans die each year from sudden cardiac death, which can often be attributed to these arrhythmias. The U.S., Germany and Japan have the highest mortality rates for AF and atrial flutter. The number of deaths per year in 2004 (the most recent year for which numbers are available) were 8,736; 6,194; and 4,899, respectively, according to the World Health Organization. |
After the baseline exam, 18 patients had improved dyssynchrony, 11 had no change and 15 had a deterioration of dyssynchrony. Of the 29 patients who had improved or unchanged dyssynchrony, five deaths occurred, and of the 15 patients who experienced deterioration of dyssyncrony, eight experienced a cardiac event. Patients who were acutely desynchronized by CRT had higher rates of composite death, HF hospitalizations and ICD shocks, says Friehling.
And rather than injecting patients with a double-dose of radiotracer to perform a second SPECT exam, patients were scanned again within four hours of the baseline exam so the radiotracer was still present in the heart, says Friehling, avoiding a duplicate dose of radiation.
Once the second image set was acquired, “we could look at the LV mechanical and see whether the device was really resynchronizing the patient,” he says.
“We found a good number of patients who actually had a deterioration in their synchrony after the device was turned on and the implication of this was that these might be the patients who go on to have more heart failure or more ICD shocks and do worse over the long term if we put a device in that actually made them worse,” Friehling notes.
Friehling says these results may open many doors for the future of clinical practice and soon with just a baseline SPECT scan practitioners will be able to decide whether or not patients should receive a CRT device and how and where the ventricular lead should be placed.
“The reason why this would be helpful on all those fronts is because when you do a nuclear SPECT study you get a lot of information—perfusion data where you can see which parts of the LV are scarred, ejection fraction information so you can decipher if the patients even meet standard criteria for CRT and then the third thing is dyssynchrony information,” he says. “So using all of that information just from a baseline scan will allow us to improve our selection criteria.”
Currently, this is being used just as a research tool for CRT. But Friehling says, “Even just using the nuclear imaging scans to obtain a more accurate ejection fraction and a way of determining scar burden it is beneficial.”
In the future, he offers that this tactic may also be useful for patients being implanted with ICDs. “Because there are really strict cutoffs on which patients will benefit or who you should put an ICD in so if we are using modalities like echo the ejection fraction is highly variable I think that nuclear imaging might be a little better for something like that too.”
Maryland researchers use PET/SPECT for VT patients
Because most arrhythmias are associated with scarring, knowledge about the location and extend of myocardial scar is critical. Dickfeld and colleagues have founded the Maryland Arrhythmia and Cardiology Imaging Group (MACIG) integrating leading clinicians and researchers in electrophysiology, radiology and basic science to find innovative approaches for this pressing clinical problems.The researchers are using cardiac PET/SPECT imaging to derive 3D scar maps and create segmental analysis to help quantitatively compare EP voltages and PET/SPECT inferred tissue properties to ultimately help guide clinical VT ablations.
Dickfeld et al found that use of PET/SPECT accurately assesses LV scar and border zones and is a useful approach to understanding the scar characterization that may not be attained through EP voltage maps (J Am Coll Cardiol Img, 2008; 1:73-82).
The 3D reconstructions can allow for the scar border zone to be evaluated and also pinpoint exactly where the VT or VF is coming from, he says. To date, UMMC has imaged close to 50 patients with PET or SPECT prior to an ablation procedure.
“These fast heart rates need scarring to exist and persist,” says Dickfeld. “That is why we need to do scar imaging. We want to know exactly where that scar is and once we have our PET scan we try to qualitatively and quantitatively define where that scar is.
“We now have the ability to cut the heart into 720 little pieces and register the metabolic data from the PET exam to the voltage data we obtain during a procedure…so we can look at the areas where we can successfully terminate the arrhythmias,” says Dickfeld.
But, University of Maryland nuclear medicine physicist Mark Smith, PhD, says finding a common reference frame to actually compare the EP voltage values with quantitative or semi-quantitative values from the PET or SPECT exams is not all that easy.
However, his facility has developed tools to automate the analysis of the EP voltages and PET/SPECT data to help facilitate this process. The cardiac images are exported in DICOM format and then analyzed using a software program (PMOD Technologies) to retrospectively map the myocardium. These data are then exported and run through spreadsheets to quantify various tracers in the patient’s heart.